Energy Savings from Honeywell Total Connect Comfort Thermostats

Energy Savings from
Honeywell Total Connect
Comfort Thermostats
October 13, 2014
Prepared for:
Smart Grid Solutions
Honeywell International Incorporated
1985 Douglas Drive North
Golden Valley, MN 55422
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Prepared by:
Bryan Ward
James Stewart, Ph.D.
Jeremy Jackson
Cadmus
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Table of Contents
Executive Summary....................................................................................................................................... 1
Introduction ............................................................................................................................................ 1
Research Methods.................................................................................................................................. 1
Main Findings ......................................................................................................................................... 2
Directions for Future Research............................................................................................................... 3
Introduction .................................................................................................................................................. 4
Honeywell Total Connect Comfort Thermostats .................................................................................... 4
Research Questions ................................................................................................................................ 5
Energy Policy Relevance ......................................................................................................................... 6
Organization of this Report .................................................................................................................... 7
Methodology................................................................................................................................................. 8
Overview................................................................................................................................................. 8
Analysis Steps ......................................................................................................................................... 9
Step 1: Developing Home Space Conditioning Energy-Use Models ................................................ 9
Step 2: Matching TCC homes to RECS homes ................................................................................ 10
Step 3: Estimating Models of Home Energy Use for Heating and Cooling .................................... 12
Step 4: Determining the Effect of TCC Thermostats on Temperature Set Points.......................... 15
Step 5: Estimating Energy Savings ................................................................................................. 15
TCC Thermostat Savings Estimates ............................................................................................................. 17
Differences in Thermostat Interior Temperature Set Points ............................................................... 17
Energy and Energy Cost Savings from TCC Thermostats ...................................................................... 19
Regional Savings Estimates ............................................................................................................ 21
TCC Thermostat Cost-Effectiveness ..................................................................................................... 24
Cost of Saved Energy for Utility Connected Thermostat Efficiency Programs .............................. 25
Conclusions ................................................................................................................................................. 28
Summary of Main Findings ................................................................................................................... 28
Future Research.................................................................................................................................... 29
References .................................................................................................................................................. 30
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Executive Summary
Introduction
Space conditioning constitutes the largest energy end-use in U.S. homes. According to the most recent
U.S. government estimates, space heating and cooling account for, respectively, 42% and 6% of
residential energy use. Consequently, policymakers looking to slow the increase in U.S. energy
consumption have focused on achieving efficiency improvements in residential space conditioning.
An opportunity exists to reduce residential energy use through enhancing users’ control of home
heating and cooling systems. In the past few years, Honeywell and other thermostat manufacturers
have introduced a new generation of residential space-conditioning control technologies: wirelesscommunicating, programmable thermostats. Users can control these thermostats from a thermostat
keypad or a web or mobile device. The enhanced control afforded by WiFi-enabled thermostats reduces
the costs of controlling the space heating and cooling systems and creates potential for energy savings
by enabling users to better align home space conditioning with occupancy and actual demand.
This paper uses data about user interactions with Honeywell connected thermostats to better
understand the thermostats’ impacts on home energy use.
Specifically, the paper answers three main questions:
1. What energy savings for home space heating and cooling do Honeywell Total Connect Comfort
(TCC) thermostats produce?
2. What energy cost savings do TCC thermostats produce?
3. How do energy and cost savings from TCC thermostats vary between climate zones within the
United States?
This study offers an advantage in covering the entire United States and providing estimates of energyuse savings for both heating and cooling. It does not consider, however, the potential benefits to utilities
of using Honeywell TCC thermostats to manage residential space-conditioning loads to obtain peakdemand savings.
Research Methods
To estimate energy savings, Cadmus compared average heating and cooling temperature set points in
homes with and without connected thermostats. Cadmus analyzed user-interface (UI) data from 2012
for almost 1,800 Honeywell TCC thermostats purchased through retail channels or space-conditioning
contractors. The UI data provided a rich source of information about how early adopters used
Honeywell connected thermostats.
To establish a baseline for Honeywell TCC thermostats, Cadmus used data on thermostat temperature
set points from the 2009 U.S. Department of Energy’s Residential Energy Consumption Survey (RECS).
This large, nationally-representative survey inquired about different energy-use aspects for home
1
heating and cooling including typical thermostat temperature set points, occupancy schedules, heating
equipment type, and house characteristics. The RECS survey constitutes a valid baseline because it
preceded widespread introduction of connected thermostats.
To minimize the potential that selection bias could compromise the comparison of thermostat set
points, Cadmus used a matching procedure, Coarsened Exact Matching (CEM), to identify RECS
households with similar incomes, home sizes, and locations as homes with TCC thermostats. The study
analyzed matched observations of RECS and TCC thermostat homes. This matching procedure reduced
the likelihood that differences in thermostat set points between homes with and without connected
thermostats would occur due to selection bias in thermostat adoption.
Finally, Cadmus used RECS data to develop econometric models of energy use for home heating and
cooling. The models, which explain energy use as a function of thermostat settings, served to estimate
energy savings from connected thermostats.
Main Findings
Overall, Cadmus’ analysis suggests Honeywell TCC thermostats purchased through retail channels or
space-conditioning contractors saved significant energy for the average adopter and adoption proved
highly cost-effective in many U.S. climate zones.
The energy savings analysis resulted in the following specific findings:

On average, Honeywell TCC thermostats would save about 5% of energy use for home space
heating and 19% of energy use for home cooling during a normal weather year. In total, TCC
thermostats would save about 7% of energy use for heating and cooling.

Honeywell TCC thermostats would save about $25 per home per year in space heating energy
costs and $91 per home per year in space cooling energy costs during a normal weather year.
The thermostats would produce total energy cost savings of $116 per home per year.

Though sample sizes are small for some climate zones, the analysis suggests energy and energy
cost savings vary significantly between zones. Savings depend on zone-specific demand for
heating or cooling and the impact of Honeywell TCC thermostats on temperature set points.

Hot-Humid and Hot-Dry/Mixed-Dry climate zones would exhibit the greatest heating energy
savings and energy cost savings during a normal weather year. Homes without connected
thermostats in these zones experienced the highest average heating temperature set points
and, therefore, present some of the greatest potential for energy savings. It is estimated TCC
thermostats would generate space-heating energy cost savings, respectively, of $70 and $39 per
home per year.

Hot-Humid and Mixed-Humid climate zones would exhibit the greatest cooling energy savings
and energy cost savings during a normal weather year. These zones include some of the most
warm and humid areas and require the greatest demand for air conditioning. It is estimated that
2
Honeywell TCC thermostats would generate estimated space-cooling energy cost savings,
respectively, of $172 and $121 per home per year.

In the Hot-Humid and Mixed-Humid climate zones, annual energy cost savings of, respectively,
$242 and $135 would exceed the $100 incremental cost of a Honeywell TCC thermostat. Homes
in the Mixed-Dry/Hot-Dry and Very Cold/Cold climate zones would achieve a positive return on
their investment after between one and two years.

The average cost of saved energy for a Honeywell TCC thermostat utility direct install program
would be $0.06 per kWh, which equals the median levelized cost of saved energy ($0.06/kWh)
for utility residential whole home or direct install program in the U.S. (LBNL, 2014).
Directions for Future Research
In conducting this research, Cadmus identified the following questions for future research:

This analysis pertains to very early adopters of Honeywell TCC thermostats. Will savings of
subsequent adopters be the same, lower, or higher?

Energy savings and energy cost savings estimates differ substantially between climate zones
(though based on relatively small analysis sample sizes). Do such differences between climate
zones remain among more recent adopters?

How do adopters of TCC thermostats achieve energy savings? Adopters could have saved energy
by reducing the intensity of space conditioning when operating heating or cooling systems or by
reducing the number of days or hours with the space-conditioning unit switched to on.

How persistent are energy savings from TCC thermostats? Do savings increase, decrease, or stay
the same with time since adoption?
Cadmus is performing a second national impact study to answer these questions. The study will analyze
UI data from 2013 for a very large number of homes with Honeywell TCC thermostats. Cadmus expects
to complete the study in 2014 and will update this study’s results, providing a more comprehensive set
of findings about energy savings from Honeywell connected thermostats.
3
Introduction
In U.S. homes, space conditioning constitutes the largest energy end use. Per the most recent U.S.
government estimates, space heating and cooling account for, respectively, 42% and 6% of residential
energy use.1 Although space conditioning’s share of residential energy consumption will likely decrease,
energy used per home for residential space conditioning will grow due to increased saturation of central
air conditioning.
Consequently, policymakers looking to slow the increase in U.S. energy consumption have focused on
achieving efficiency improvements in residential space conditioning. Policies aimed at increasing space
heating and cooling efficiency have been effective, encouraging adoption of better insulation, doublepaned windows, and efficient furnaces, heat-pumps, and air conditioners.2 Despite these achievements,
significant opportunities remain to reduce energy use for home space conditioning.
Enhancing user control of home heating and cooling systems offers an opportunity for increasing energy
savings. In the 1990s, the U.S. government’s ENERGY STAR program encouraged adoption of
programmable thermostats, which allowed users to schedule heating and cooling in their homes; energy
savings from programmable thermostats, however, have proved elusive.3
During the past few years, Honeywell and other thermostat manufacturers have introduced a new
generation of residential space-conditioning control technologies: wireless-communicating,
programmable thermostats. Users can use these thermostats to control the heating and cooling system
from the thermostat keypad or a web or mobile device. The enhanced control afforded by WiFi-enabled
thermostats reduces control costs and creates potential for energy savings by enabling users to better
align home occupancy patterns with space heating and cooling.
Honeywell Total Connect Comfort Thermostats
Honeywell introduced the first WiFi-enabled Total Connect Comfort (TCC) thermostats in 2012. A wallmounted communicating programmable thermostat, the TCC thermostat offers a user interface and
mobile and web applications. These applications allow users to connect to their thermostats and to
adjust settings and temperature set points remotely via phone, tablet, or computer. Figure 1 shows a
recent TCC thermostat model.
1
U.S. Department of Energy analysis of 2009 RECS. Available at
http://www.eia.gov/todayinenergy/detail.cfm?id=10271&src=%E2%80%B9%20Consumption%20%20%20%20
%20%20Residential%20Energy%20Consumption%20Survey%20%28RECS%29-f1
2
For example, see Aroonruengsawat, Auffhammer, and Sanstad (2009) and Jacobsen and Kotchen (2010).
3
The U.S. EPA suspended its ENERGY STAR programmable thermostat on December 31, 2009, after questions
arose regarding the thermostats’ net energy savings and environmental benefits. See
https://www.energystar.gov/index.cfm?c=archives.thermostats_spec and Peffer, Pritoni, Meier, Aragon, and
Perry (2011).
4
Figure 1. Example of Honeywell WiFi Thermostat (WiFi 9000)
Honeywell designed the TCC thermostats to provide the following features:

Mobile connectivity for remote user-control of the thermostat;

Ease of use and programming compliance; and

Third-party communication and control for utility direct-load control programs.
Honeywell sells TCC thermostats through retail, trade, and utility channels. Homeowners purchase
connected thermostats for a variety of reasons, including increased convenience of use, enhanced
thermal comfort in the home, and reduced household energy use and costs.
Research Questions
While the mobile connectivity of connected thermostats increases convenience and reduces the costs of
controlling home heating and cooling, its impact on energy use remains less certain.
To understand the potential impacts, consider a typical U.S. household using a traditional programmable
or non-programmable thermostat and seeking to maintain the home’s interior at a particular
temperature. The preferred temperature may change with the season, day of the week, and hour of the
day, and depends on the home’s occupancy, occupants’ thermal comfort, and energy costs. The cost of
controlling the thermostat, requiring users to be in the home, may prevent them from achieving their
preferred temperatures, and the home may be too hot or too cold.
Mobile connectivity can help users to achieve their preferred temperatures. Enhanced control of the
thermostat affects energy use for heating and cooling along two margins:

First, thermostat users may heat or cool the home more or less intensively (i.e., cool or heat the
home to a higher or lower temperature) while the home is space-conditioned. Cadmus calls
these changes on the “intensive margin.”
5

Second, thermostat users may increase the amount of time (e.g., the number of days or hours
during the year) that they heat or cool the home. Cadmus calls these changes on “the
extensive margin.”
Energy savings occur if mobile connectivity causes a net decrease in heating or cooling energy use
because of changes on the intensive or extensive margins. As noted, mobile connectivity may allow
users to better align home heating and cooling with occupancy patterns—that is, to achieve savings
along the extensive margin. By reducing control costs, mobile connectivity also may allow users to heat
or cool less while the home is occupied—that is, to achieve savings along the intensive margin. For
example, using a mobile phone application, energy-efficient temperature set points can be adjusted in
the home without visiting the wall-mounted unit. To the extent that wasteful heating and cooling can be
eliminated without sacrificing thermal comfort, reductions in energy use would represent an
unambiguous increase in efficiency.
Ultimately, however, energy savings from connected thermostats remain an empirical question that can
be answered only by studying how people use them. This paper seeks to use data about user
interactions with Honeywell connected thermostats to better understand the thermostats’ impacts on
home energy use.
Specifically, the paper answers three questions:
1. What home space heating and cooling energy savings do Honeywell TCC thermostats produce?
2. What energy cost savings do the TCC thermostats produce?
3. How do energy and cost savings from TCC thermostats vary between U.S. climate zones?
Cadmus answered these questions by comparing average heating and cooling temperature set points in
homes with and without connected thermostats and then estimating energy savings as a function of the
difference. For a given home and length/severity of the heating (cooling) season, a higher (lower)
average heating temperature set point results in greater energy use. Conversely, a lower average set
point results in lower energy use for heating, thus producing greater savings.
Cadmus analyzed user-interface (UI) data from 2012 for almost 1,800 Honeywell TCC thermostats in
homes across the United States. The UI data provided a rich source of information about how early
adopters of Honeywell connected thermostats used them. To establish a baseline for connected
thermostat use, Cadmus analyzed household survey response data on thermostat set points from the
2009 Residential Energy Consumption Survey (RECS).
Energy Policy Relevance
Energy savings from connected thermostats are worth study as the United States faces a growing
imperative to increase energy efficiency and reduce greenhouse gas emissions. Many states have set
energy-efficiency portfolio standards that mandate annual reductions in energy use against a baseline.
The federal government and states also have set increasingly stringent energy-efficiency building codes
6
and appliance standards, establishing minimum efficiency levels for new building construction and
appliances. Finally, EPA’s proposed rule 111-D, regulating emissions from existing thermal power plants,
encourages states to reduce emissions by increasing site (end-use) energy efficiency as well as efficiency
of thermal electric generators.
This imperative has left regulators, policy makers, and utilities responsible for implementing efficiency
policies looking for new opportunities to increase residential energy savings. The residential sector
accounts for 22% of national end-use energy consumption, and, as noted, space conditioning remains
the largest residential energy end use. Thus, space conditioning presents an obvious potential source of
energy savings, and connected thermostats may offer a means to achieve some savings.
Little evidence exists, however, about energy savings from connected thermostats. The technology
remains new, and industry has commissioned few energy-savings studies. Several utilities plan to
operate (or are operating) pilot programs to test energy savings from connected thermostats, but, while
these studies will provide valuable evidence, they present a small scope and may have limited
applicability in other areas of the country.
This study offers an advantage in covering the entire United States and providing estimates of energyuse savings for both heating and cooling.
Organization of this Report
This report is organized as follows:

The second (next) section describes the study methodology, including model development, data
collection, model estimation, and energy and cost savings estimation.

The third section presents estimates of the differences in thermostat set points between homes
with and without Honeywell TCC thermostats and estimates of energy and energy cost savings
from connected thermostats.

The fourth section concludes and describes questions for future research.
7
Methodology
Overview
Honeywell provided Cadmus with UI data for a sample of 1,769 TCC thermostats installed in U.S. homes.
Each thermostat in the sample was installed before January 2012 and had 12 months of UI data
between January 2012 and January 2013. Users purchased the thermostats from retail outlets or home
space-conditioning contractors. As connected thermostats remained a relatively new product offering,
TCC thermostats purchasers during this period can be considered early adopters.
The UI data provided a rich view of how users interacted with their connected thermostats. When a TCC
thermostat senses an automatic or manual change to the thermostat settings or a change in the home’s
environment, the thermostat sends a report to Honeywell. A report includes a timestamp, heating and
cooling temperature set points, the interior temperature of the home, outdoor temperature, indoor
humidity, outdoor humidity, the relay status of heating and cooling systems, schedules for home heating
and cooling, and other fields. A thermostat may generate a few to a dozen reports per hour and
thousands or tens of thousands of reports per year.4
The UI data, however, presented some limitations when estimating energy savings from connected
thermostats:

First, the data do not provide direct information about energy use, and actual spaceconditioning equipment run times could not be inferred.5

Second, UI data only cover the post-adoption period and do not include information about
thermostat settings prior to adoption.
To establish a baseline for TCC thermostats, Cadmus relied on data from the U.S. Department of
Energy’s (DOE) Residential Energy Consumption Survey (RECS). In 2009, DOE surveyed 12,083 U.S.
households regarding different energy-use aspects for home heating and cooling, including:

Space-conditioning equipment types;

Thermostat types (programmable or non-programmable);

Thermostat settings by season and time of day;

Occupancy patterns; and

Housing characteristics (e.g., floor space, number of floors).
4
The UI data of the analysis sample did not include information on whether users accessed a TCC thermostat
with a mobile device or via the web, as opposed to a thermostat touchpad.
5
This study’s UI data did not capture space conditioning system relay status. As this study’s UI data did not
include thermostat calls for heating or cooling, Cadmus could not estimate run-times for space conditioning
units. Further, as users purchased thermostats through a retailer or home space-conditioning contractor and
not a utility program, utilities could not provide data on home electricity or gas use.
8
We established a baseline for TCC thermostat homes using thermostat set points of RECS homes with
programmable or non-programmable thermostats. The 2009 RECS provides a valid baseline as the
survey preceded the widespread market introduction of connected thermostats.
As this study relied on a comparison of temperature set points between homes with TCC thermostats
and those in the RECS without them, a threat to the study’s internal validity was unobservable
characteristics that would cause adopters of TCC thermostats to choose more efficient temperature set
points. For example, TCC thermostats purchasers could have been more likely to be employed and thus
have lower daytime home occupancy rates, reducing their average temperature set points for heating. If
the analysis does not account for their lower home occupancy rates, TCC adopters would select lower
heating temperature set points, regardless of the thermostat type in their homes.
To minimize the potential for such omitted variable bias, Cadmus used a matching procedure—CEM—to
identify RECS households with similar incomes, home sizes, and locations as homes with TCC t-stats; we
did this before estimating differences in thermostat set points between homes with and without
connected thermostats. Cadmus then performed the analysis on matched observations in the RECS and
UI data. This matching procedure reduced the likelihood that differences in thermostat set points
between homes with and without connected thermostats resulted from unrelated factors.
Cadmus also used information about energy use for home heating and cooling in the RECS to estimate
the relationship between temperature set points and space conditioning energy use. The study
developed econometric models directly from thermodynamic models of energy use for home heating
and cooling, estimating them with data on RECS homes matched to TCC thermostat homes. Energy
savings from connected thermostats could then be estimated as a function of the difference in average
temperature set points between homes with and without connected thermostats.
Analysis Steps
Specifically, Cadmus estimated energy savings from TCC thermostats using the following five steps:
1. Developing models of energy use for space heating and cooling.
2. Matching TCC homes to RECS homes using CEM.
3. Estimating cooling and heating energy-use models with matched RECS data.
4. Determining thermostat set points for TCC and RECS homes.
5. Estimating energy savings as a function of difference in set points between TCC and
RECS homes.
The remainder of this section describes each of these analysis steps in greater detail.
Step 1: Developing Home Space Conditioning Energy-Use Models
Cadmus’ first developed econometric models of home energy use for space heating and cooling. The
models related space conditioning energy use to thermostat temperature set points.
9
Cadmus derived the estimating equations directly from thermodynamic models of home energy use for
heating and cooling. These models accounted for:

The home envelope area;

Wall and ceiling R values;

Space-conditioning equipment efficiency; and

The difference between the average thermostat set point and the average
outdoor temperature.
The estimating equations took the following form:
e = g(ceiling area x T , wall area x T, equipment type)
(Equation 1)
Where:
e
= Average energy use per hour for heating (cooling) in kBTUs.
Ceiling Area
= Estimate of home ceiling area in square feet.
T
= The difference between the average thermostat set point and the average
outside temperature.
Wall Area
= Estimate of home exterior wall area in square feet.
Coefficients in the heating (cooling) model indicated average energy use per hour, per square foot of
floor space, for each degree of difference between the thermostat set point and outdoor temperature.
The coefficients had an explicit interpretation for home thermodynamics: they represented the product
of the average R value for the home’s envelope and the efficiency of the home’s space conditioning
equipment.
Step 2: Matching TCC homes to RECS homes
Next, Cadmus developed the RECS analysis sample, used to establish a baseline for connectedthermostat homes. Cadmus used the CEM procedure to identify households in the 2009 RECS similar to
adopters of connected thermostats.6 We expected that households with the greatest expected benefit
of a connected thermostat would have been most likely to purchase one. Such households were likely
large consumers of energy for space conditioning. The purpose of employing CEM was to identify nonpurchasing households that were most like purchasers. CEM, a matching procedure used in social
scientific research for estimating causal effects, reduces imbalances between a treatment group (e.g.,
TCC thermostat homes) and a control group (e.g., RECS homes), increasing the likelihood that observed
differences between treatment and control group result from a causal effect of the treatment.
CEM involves four steps:
1. Identify the matching variables.
6
CEM references here.
10
2. Coarsen each matching variable, creating bins for different ranges of values for the variable.
3. Identify treatment and control group observations that correspond exactly in terms of
coarsened matching variables.7 These observations belong to the same stratum, defined by
specific ranges or bins for each matching variable.
4. Drop the coarsened data and perform analysis on matched observations using original data.
Cadmus performed CEM on TCC thermostat and RECS homes using the following variables as major
drivers of energy use for home heating and cooling:

Household income

Home floor space (sq. ft.)

Reportable domain8

Building America Climate Zone9
Cadmus obtained data on these variables for TCC thermostat homes from InfoGroup, a supplier of
household-level data on demographics and housing characteristics, and obtained the same variables for
RECS homes from the survey.10
Table 1 shows the matching procedure results for TCC thermostat and RECS homes.
Table 1. Matched Analysis Samples
Table Heading
Before CEM
After CEM
TCC thermostat homes
RECS households
1,769
12,083
653
2,578
The final analysis sample included 653 TCC thermostat homes and 2,578 RECS households. TCC
thermostat homes and RECS households exactly matched in terms of the coarsened values of household
income, home floor space, reportable domain, and climate zone. Cadmus compared matched TCC
thermostat and RECS homes on the basis of other variables and found fairly strong correspondences.
7
CEM weights.
8
Reportable domain is a RECS variable that indicates the location of the home in one of 27 states or small
groupings of states (e.g., Kansas, Nebraska, North Dakota, and South Dakota).
9
Building American climate zone definitions can be found here:
http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/ba_climateguide_7_1.pdf
10
Cadmus did not use more variables for matching as additional variables would have resulted in excessive
attrition of TCC thermostat homes from UI data. Many TCC thermostat homes had missing values for one or
more variables in the InfoGroup data and could not be matched to the RECS.
11
Figure 2 displays: the locations of TCC thermostat homes matched to the RECS; and homes not matched.
Purple indicates homes matched to the RECS, and yellow indicates those not matched. The size of the
circle indicates the number of homes in an area.
Figure 2. Geographic Distribution of TCC Thermostat Homes
Source: Cadmus analysis of locations of TCC thermostat adopters in 2012
As shown, early adopters of connected thermostats primarily lived in major urban areas of the
Northeast, Middle Atlantic, Midwest, and West Coast. The South and Mountain West indicated relatively
few connected thermostats, except for the cities of Dallas, Atlanta, and Salt Lake City. Notably, the
Southwest exhibited few adopters of connected thermostats. Similar spatial distributions distinguished
connected thermostat homes matched to RECS and those not matched to RECS.
Step 3: Estimating Models of Home Energy Use for Heating and Cooling
In the third step, Cadmus estimated the econometric models of home energy use for heating and
cooling using matched RECS data. The models took the specifications indicated by Equation 1. Cadmus
estimated: the models of heating energy use for each climate zone and heating equipment type; and the
models of cooling energy use for each climate zone.
Estimating Equation 1 required an estimate of the number of heating days (i.e., a day with an average
outside temperature less than 65⁰F) and an estimate of the average outside temperature across heating
12
days in 2009 for each RECS home.11 For this purpose, Cadmus used hourly temperature data for 2009
from hundreds of National Oceanic and Atmospheric Administration U.S. weather stations. Cadmus
calculated the number of heating days and average outside temperatures during heating days for each
reportable domain and Building America climate zone combination. The study estimated the number of
hours during the heating season as 24 hours * number of days with average temperatures below 65⁰F.
Cadmus estimated the number of cooling days as the number of days with average outside daytime
temperatures above or equal to 75⁰F.
Cadmus then estimated Equation 1 by weighted least squares, with weights obtained from the CEM
procedure. These weights controlled for differences between treatment and control groups in strata
sizes: that is, in the number of matched observations. Cadmus estimated White standard errors to
account for heteroskedasticity (i.e., non-constant variance of the error term).
For all climate zones, the estimated coefficients in the heating and cooling models were positive and
statistically significant. As noted, these coefficients indicated energy-use intensities per degree of
difference between the thermostat average temperature set point and the average outside
temperature. Cadmus verified that on average, the models yielded accurate predictions of energy use
for homes in the analysis sample.
Using the regression results, Cadmus estimated the percent of energy savings and energy cost savings
resulting for a home adjusting its thermostat setting downward (upward) by one degree during the
heating (cooling) season. The estimates applied to U.S. households with house sizes, incomes, locations,
and climates similar to those of TCC thermostat adopters. This analysis did not indicate energy savings
from connected thermostats, a calculation that first requires estimating the impact of connected
thermostats on temperature set points.
Figure 3 and Figure 4 show, respectively: energy and dollar cost savings estimates for matched U.S.
households from a 1⁰F change in temperature set points. The energy savings estimates assumed normal
weather (TMY 2010) and the energy cost savings assumed residential retail prices for energy (e.g.,
electricity, natural gas, and fuel oil) in 2013, as reported by the Energy Information Administration (EIA).
11
RECS reports heating degree days (base temperature 65⁰F) and cooling degree days (base temperature 65⁰F),
but not average outside temperatures. To calculate average temperatures during the heating or cooling
season, one must know the number of days with temperatures greater than 65⁰F.
13
Figure 3. Percent Energy Savings for Heating from 1⁰F Adjustment of Thermostat Setting
14%
12.1%
12%
10%
8%
6%
5.7%
4.3%
4%
2%
0%
Heating
Cooling
Total
Notes: Results based on Cadmus analysis. See text for details.
Adjusting the temperature set point downward by an average of 1⁰F would save 4.3% of energy use for
heating. Savings depended on a number of factors, including: the demand for space conditioning, the
efficiency of space conditioning equipment, and the thermal efficiency of the home’s envelope.
Similarly, for cooling, adjusting the thermostat upward by an average of 1⁰F would save 12.1% of cooling
energy use. Together, the adjustments would save 5.7% of a home’s energy use for space conditioning.
As space conditioning accounts for 40-50% of energy use in a typical U.S. home, energy savings from TCC
thermostats would equal about 2.5% of home energy use.
Figure 4. Energy Cost Savings for Cooling from 1⁰F Adjustment of Thermostat
$90
$80
$70
$60
$50
$40
$30
$20
$10
$0
$85
$61
$24
Heating
Cooling
Notes: Results based on Cadmus analysis. See text for details.
14
Total
Using the EIA retail energy price data, Cadmus translated these energy savings into cost savings.
Decreasing a home’s thermostat setting by an average of 1⁰F would save $24 in heating costs for the
average home, and increasing a home’s thermostat setting by 1⁰F would save $61 in cooling costs for
the average home. Total cost savings would average $85 per home.
Step 4: Determining the Effect of TCC Thermostats on Temperature Set Points
Cadmus estimated the difference in average temperature set points for heating and cooling between
matched TCC thermostat homes and RECS homes. Due to CEM, differences in temperature set points
accounted for the impacts of household incomes, home sizes, reportable domains, and climate zones on
thermostat settings.
Cadmus estimated temperature set points in TCC thermostat homes as the average set point between
December and March during hours with the home’s heating system switched to on. The study limited
the analysis to the December to the end of March period to remain consistent with the RECS, which
asked respondents to report thermostat set points for heating “during winter.” Similarly, for cooling,
Cadmus estimated thermostat average temperature set points in TCC thermostat homes as the average
during the summer months of June, July, August, and September, with cooling systems switched to on.
RECS asked respondents to report thermostat set points “during summer.”
Step 5: Estimating Energy Savings
The final analysis step estimated energy and energy cost savings for heating and cooling from TCC
thermostats. The following equation estimated energy savings for a normal weather year:
TCC thermostat energy savings per home = F x s x h
(Equation 2)
Where:
F = difference between matched TCC thermostat homes and RECS homes in average thermostat
temperature set points
s = regression-based estimate of energy savings per hour, per degree of setback for the
average home
h = heating (cooling) hours in a normal weather year
Calculating s—the energy savings (in kBTUs) per hour, per degree of setback—required evaluating
Equation 1 for particular values of roof and exterior wall areas. Cadmus selected the average roof and
wall areas in the analysis sample or climate zone analysis subsample for this calculation.
Cadmus estimated the energy cost savings as:
TCC Thermostat energy cost savings = p * TCC thermostat energy savings per home
Where:
p = the average retail price per kBTU for energy used in heating or cooling
15
(Equation 3)
Cadmus then estimated p for heating using EIA data on 2013 residential retail prices of electricity,
natural gas, and heating oil during the heating months of December, January, February, and March. The
analysis determined p as a weighted average of these prices, with weights equal to each energy source’s
share of total energy use in kBTUs. The analysis also determined p for cooling using 2013 EIA data on
electricity prices during the cooling months of June, July, August, and September.
The following section presents energy savings and energy cost savings estimates for heating and cooling
for an average home in each climate zone and in the United States.
16
TCC Thermostat Savings Estimates
Cadmus estimated energy savings for home heating and cooling from Honeywell TCC thermostats as a
function of the difference in average temperature set points between homes with and without TCC
thermostats. This section presents estimates of the differences in thermostat set points, followed by
estimates of annual energy savings and energy cost savings.
Differences in Thermostat Interior Temperature Set Points
Figure 5 shows average heating temperature set points in matched Honeywell TCC thermostat homes
and RECS homes.
Figure 5. Average Thermostat Temperature Set Points—Heating Season
70
69.0
69
68
67.4
67.3
○F
66.0
66
65
67.1
66.8
67
66.3
66.1
66.5
66.0
65.0
64.9
64
63
62
Hot-Dry/Mixed-Dry
Hot-Humid
Marine
TCC Tstat Set Points
Mixed-Humid
Very Cold/Cold
All climate zones
RECS Tstat Set Points
Note: TCC thermostat set points estimated for hours with heating systems switched to on, between December and
March. All differences were statistically significant at the 5% level, except in the Very Cold/Cold region.
Matched RECS homes exhibited an average heating temperature set point of 67.1⁰F. Significant
differences occurred, however, in set points between climate zones. Homes in warm or temperate
regions of the United States (such as the Hot-Humid, Hot-Dry/Mixed Dry, and Mixed-Humid climate
zones) exhibited higher average set points. These differences could reflect differences in residents’
tolerance for cold and thermal comfort between U.S. regions. As these climate zones produced higher
average temperature set points, they likely offered greater potential for energy savings.
The difference in average heating temperature set points between TCC thermostat and RECS homes was
1.1⁰F, indicating homes with connected thermostats were heated at lower levels by approximately 1⁰F.
This difference proved statistically significant at the 5% level. Notably, as this average difference
occurred across all hours, it can be considered large.
17
In each climate zone (except Marine), TCC thermostat homes exhibited lower average heating
temperature set points.12 All climate zone differences in thermostat set points proved statistically
significant, except for the Very Cold/Cold Climate zone. The biggest differences in average heating
temperature set points occurred in the Hot-Humid and Hot-Dry/Mixed-Dry climate zones.
Figure 6 presents estimates of average cooling temperature set points for homes with and without TCC
thermostats. RECS homes exhibited an average thermostat set point of 74.2⁰F. Homes in the Very
Cold/Cold and Marine climate zones exhibited the lowest average set points and thus offered the
greatest potential for energy savings.13
12
Cadmus investigated several hypotheses to explain why average temperature set points in the Marine climate
zone were 1.3 degrees higher in TCC thermostat homes. Cadmus did not find any outliers in average
temperature set points in TCC thermostat or RECS homes. We also looked for differences between RECS and
TCC thermostat homes in locations and micro-climates within the Marine climate zone. RECS reported only the
state and climate zone for each home, so it was not possible to identify their precise locations and to directly
compare them to the locations of TCC thermostat homes. However, using postal codes, Cadmus plotted the
locations of TCC thermostat homes and did not find any unusual location patterns. The homes were clustered
around the population centers of Portland, Seattle, San Francisco, Oakland, and San Jose. Another hypothesis
is that there was strong positive selection in space-conditioning energy use: Purchasers of connected
thermostats may have intensively heated or cooled their homes and had high average temperature set points
in winter or low average temperature set points in summer as a consequence. Finally, the number of TCC
thermostat homes in the Marine climate zone (N=51) in the analysis sample was small, so analysis of a larger
sample might yield a different result.
13
We do not report estimates for the Marine climate zone as the zone did not produce sufficient homes with air
conditioning to estimate savings. The Marine climate zone accounted for about 8% of the TCC thermostats in
the sample. The distribution of remaining homes in the TCC thermostat analysis sample across other climate
zones was as follows: Hot-Dry/Mixed-Dry, 10%; Hot-Humid, 15%; Mixed-Humid, 27%; and Very Cold/Cold,
40%.
18
Figure 6. Average Thermostat Temperature Set Points—Cooling Season
78
77
76.9
76.7
76.2
76
76.1
75.8
75.6
75.3
75
○F
74.2
74
73.3
73.5
73
72
71
Hot-Dry/Mixed-Dry
Hot-Humid
Mixed-Humid
TCC Tstat Set Points
Very Cold/Cold
All climate zones
except marine
RECS Tstat Set Points
Notes: TCC thermostat set points estimated for hours when cooling system switched to on, between June
and September. All differences were statistically significant at the 5% level, except in the Hot-Dry/Mixed-Dry
climate zone.
The difference in average cooling temperature set point between TCC thermostat homes and RECS
homes was 1.9⁰F, indicating TCC thermostat homes were cooled an average of 2⁰F less. In each climate
zone, TCC thermostat homes exhibited higher average temperature set points. All differences in
thermostat set points proved statistically significant, except for the Hot-Dry/Mixed-Dry climate zone.
In summary, the comparison of thermostat set points suggests homes with TCC thermostats used less
energy for heating and cooling. Homes with TCC thermostats experienced lower average temperature
set points for heating and higher average temperature set points for cooling.
Energy and Energy Cost Savings from TCC Thermostats
As described in the methodology section, Cadmus used results from the space conditioning energy use
models to estimate energy savings per home from TCC thermostats. In addition to the difference in
temperature set points between TCC thermostat and RECS homes, energy savings estimates
depended on:

Demand for heating or cooling;

The efficiency of space conditioning equipment; and

The thermal efficiency of the home’s envelope.
19
For example, homes in the Hot-Humid region experienced higher demand for cooling during summer
and, with all else equal, would have greater energy savings than homes in the rest of the United States.
Cadmus estimated energy savings assuming normal weather. Energy cost savings also depended on the
retail price of energy.
As Figure 7 shows, the average U.S. home with a Honeywell connected thermostat reduced energy use
for heating by 4.5% and 19.4% for cooling during a normal weather year. Cooling produced a larger
percentage energy savings than heating because the difference in average temperature set points
between TCC thermostat and RECS homes constituted a larger percentage of the difference between
the average temperature set point and the average outdoor temperature during the cooling season.
Figure 7. TCC Thermostat Percent Space Conditioning Energy Savings in Normal Weather Year
25%
19.4%
20%
15%
10%
6.6%
5%
4.5%
0%
Heating
Cooling
Total
Note: Results based on Cadmus analysis. See text for details.
Overall, energy savings for space conditioning from TCC thermostats would be 6.6% during normal
weather—an estimate much closer to estimated percent savings for heating, as heating accounts for
seven times as much home energy use as cooling (42% vs. 6%).
Figure 8 shows heating and cooling energy cost savings for U.S. homes. The average home with a TCC
thermostat would save $25 in energy costs for heating and $91 in energy costs for cooling during a
normal weather year. Total energy cost savings from space heating and cooling would equal $116.
20
Figure 8. TCC Thermostat Annual Energy Cost Savings Per Home
$140
$116
$120
$100
$91
$80
$60
$40
$25
$20
$0
Heating
Cooling
Total
Notes: Estimates of cost savings assume a normal weather year and 2013 energy prices. See the
methodology section for estimation details.
Regional Savings Estimates
Figure 5 and Figure 6 show significant differences between climate zones regarding the impacts of TCC
thermostats on average heating and cooling temperature set points. How did these differences affect
climate zone energy and energy cost savings?
Figure 9 and Figure 10 show climate zone estimates of TCC thermostat percent energy and energy cost
savings for, respectively, heating and cooling. Also, Figure 9 shows savings of natural gas for space
heating in therms, and Figure 10 shows savings of electricity for space cooling in kWh.14 Significant
differences occurred in energy and cost savings between climate zones, with the greatest contributing
factor as difference in average temperature set points between homes with and without connected
thermostats (though other factors, such as the demand for air conditioning, thermal efficiency of the
home’s envelope, and energy costs contributed).
Per the analysis of climate-zone energy savings shown in Figure 9, the Hot-Humid and Hot-Dry/Mixed
Dry climate zones produced the greatest energy savings for space heating. The average TCC thermostat
home in these zones saved about 18% and 16%, respectively, of energy use for heating during a normal
14
Cadmus translated average kBTU energy savings for space heating into therms. While the percent and cost
savings in Figure 9 and Figure 10 represent averages across homes that used natural gas, electricity, or fuel oil for
space heating, natural gas was the predominant fuel source in each climate zone. In the Hot-Dry/Mixed-Dry,
Marine, and Very Cold/Cold climate zones, 90% or more of energy use for space heating came from natural gas. In
the Hot-Humid and Mixed-Humid zones, about 83% of energy use for space heating came from natural gas.
21
weather year. These savings correspond to about 36 and 38 therms per home per year. Notably, these
two regions exhibited the highest average temperature set points and, thus, some of the greatest
potential for savings. The Hot-Humid and Hot-Dry/Mixed dry climate zones exhibited substantial energy
cost savings, equal to $70 and $39, respectively.
In contrast, despite exhibiting the greatest space-heating demand (and thus large potential energy
savings), homes in the Very Cold/Cold and Mixed-Humid climate zones offered a very small energy and
energy cost-savings during a normal weather year, largely due to minor difference in average
temperature set points between TCC thermostat homes and RECS homes, as shown in Figure 5.
Figure 9. TCC Thermostat Space Heating Energy and Cost Savings by Climate Zone
-$50
-8.4%
-43 therms
$9
1.3%
10 therms
$39
16.0%
36 therms
$70
18.1%
38 therms
$15
2.6%
13 therms
Source: Cadmus analysis. See text for details.
Cadmus’ analysis of cooling energy savings by climate-zone in Figure 10 shows the most humid regions
of the United States achieved the greatest energy and energy cost-savings. In the Hot-Humid and MixedHumid climate zones, homes saved, on average $172 and $121, respectively, per home in a normal
weather year. Homes in these humid climate zones produced high demand for air conditioning.
22
Figure 10. TCC Thermostat Space Cooling Energy and Cost Savings by Climate Zone
N/A
$47
19.7%
326 kWh
$18
4.0%
132 kWh
$121
29.1%
903 kWh
$172
14.1%
1,121 kWh
Source: Cadmus analysis. See text for details.
Homes in the Hot-Dry/Mixed-Dry climate zone exhibited a small percent of energy savings and energy
cost savings, an effect explained (as shown in Figure 2) by the few homes with TCC thermostats in the
desert Southwest. Rather, most TCC thermostat homes in the Hot-Dry/Mixed-Dry climate zone were
located in more temperate coastal Southern California.
Homes in the Very Cold/Cold climate zone achieved large percentage of energy savings for cooling
(19.7%) and modest energy cost savings of $47 per home during a normal weather year. Homes in this
zone exhibited low average cooling temperature set points and high potential for energy savings: the
high percentage savings reflect this potential. However, homes in this zone also exhibited small total
cooling loads, limiting the energy savings potential. The modest energy cost savings reflected relatively
low demand for space cooling.
Figure 11 shows the sum of space-heating and space-cooling energy savings and energy cost-savings
from Honeywell TCC thermostats. Total space-conditioning energy savings during a normal weather
year are greatest in the Mixed-Humid and Hot-Humid climate zones.
23
Figure 11. TCC Thermostat Total Space Conditioning Percent Energy and Cost Savings by Climate Zone
N/A
$57
2.7%
$57
12.0%
$135
7.0%
$242
15.8%
Source: Cadmus analysis. See text for details.
TCC Thermostat Cost-Effectiveness
Many homeowners seeking to reduce home heating and cooling costs will want to compare the
expected energy cost savings with the incremental cost of a TCC thermostat. Energy-efficiency
policymakers will also be interested in this comparison because in many jurisdictions rate-payer funded
efficiency measures are required to pass the Participant Cost Test, a comparison of the benefits and
costs of the customer installing the measure.
Table 2 shows the annual energy cost savings per home and the approximate payback period, the
minimum number of years required to achieve energy cost savings equal to the incremental cost of a
TCC thermostat relative to a standard programmable thermostat. To calculate the payback period,
Cadmus assumed an incremental cost of $100 and discounted energy cost savings at an annual rate of
8%.
24
Table 2. TCC Thermostat Payback Period
Annual energy
Approximate
Climate Zone
cost savings per
Payback Period
home
Hot-Dry/Mixed-Dry
<2 years
$57
Hot-Humid
$242
<1 year
Mixed-Humid
$135
<1 year
Very Cold/Cold
$57
<2 years
All climate zones except marine
$116
<2 years
Notes: Payback period was estimated as the minimum number of years
required to achieve average energy cost savings equal to the incremental
cost of a TCC thermostat. Annual energy cost savings equal sum of heating
and cooling energy cost savings. Analysis assumes the discount rate equals
8%, the incremental cost of connected thermostat equals $100, and that
future energy prices do not change from 2013 levels. We did not report a
payback period for Marine climate zone because this zone's cooling energy
cost savings was not estimated.
Depending on the climate zone, the average annual energy cost savings per home (the sum of heating
and cooling energy cost savings) ranged between $57 and $242, and the payback period for TCC
thermostats ranged from one to two years. This means that it would take one or two years for the
average home to save $100 in energy costs and to cover the additional cost of a TCC thermostat. Homes
in the Hot-Humid and Mixed-Humid climate zones have the greatest annual energy cost savings and
shortest payback period (less than one year). As energy cost savings were smaller, homes in the Very
Cold/Cold and Hot-Dry/Mixed-Dry region have longer payback period of between one and two years.
Across U.S. climate zones except Marine, the average annual energy cost savings were $116 per home
and the average payback period was between one and two years.
In summary, these results suggest that adoption of TCC thermostats would be very cost-effective for
households in many climate zones.
Cost of Saved Energy for Utility Connected Thermostat Efficiency Programs
While this paper analyzed data from Honeywell TCC thermostats purchased through retail or trade
contractor channels, electric and gas utilities may want to know the average cost of saved energy from
connected thermostats deployed through energy efficiency programs. In this section, we present
estimates of the cost of saved energy for a representative utility direct-install efficiency program
involving Honeywell TCC thermostats. We provide separate estimates of utility average cost of kWh
savings from space cooling and utility average cost of therm savings from space heating. To estimate the
average cost of saved energy, Cadmus used the TCC thermostat energy-savings estimates in Figure 9 and
Figure 10 and assumptions about the costs of administering a direct-install efficiency program.
Cadmus estimated the average cost of saved energy under different assumptions about the utility’s
average cost of deploying a connected thermostat, including low-cost and high-cost scenarios. We
25
assume the cost of administering the program include the costs of program design, direct marketing,
hardware acquisition, contractor training and certification, participant recruitment and incentives,
contractor installation of the thermostats, and program evaluation. The high costs scenario would
correspond to smaller programs or those with more expensive direct marketing, recruitment, contractor
training, and installation costs. We assume a cost of $400 per thermostat for the low costs scenario and
$700 per thermostat for the high costs scenario.
We estimated the average cost of saved energy as the utility’s average cost of deploying a TCC
thermostat in a home divided by the thermostat’s average lifetime energy savings. To estimate lifetime
savings, we assumed that the average lifetime of a TCC thermostat was 10 years and multiplied the
average life time the average annual energy savings per thermostat.
Table 3 shows estimates by climate zone of utility average cost of kWh savings from space cooling and
average cost of therm savings from space heating. We estimated the costs of saved energy for space
heating and cooling independently, that is, we did not account that a utility could use the thermostats to
save both heating and cooling energy.
Table 3. Average Cost of Saved Energy for TCC Thermostat Efficiency Program
Space Cooling Energy Savings
Space Heating Energy Savings Costs
Costs ($/kWh)
($/therm)
Low Program
High Program
High Program
Low Program
Climate Zone
Costs Scenario
Costs Scenario
Costs Scenario
Costs Scenario
Hot-Dry/Mixed-Dry
$1.97
$0.30
$0.53
$1.12
Hot-Humid
$0.04
$1.87
$0.06
$1.07
Mixed-Humid
$0.04
$0.08
$2.96
$5.18
Very Cold/Cold
$0.12
$0.21
$4.23
$7.40
All climate zones except
marine
$0.06
$0.11
$2.17
$3.79
Notes: Average cost of energy savings estimated as the assumed cost per installed TCC thermostat divided by
average lifetime thermostat savings. Cadmus assumed TCC thermostats have an average life of 10 years. Low
program costs scenario assumes program average deployment cost per thermostat of $400. High costs scenario
assumes program average deployment cost per thermostat of $700. See text for estimation details.
Across the U.S., utility average cost of cooling savings would be $0.06/kWh for the low program costs
scenario and $0.11/kWh for the high program costs scenario. The cost of saved energy for the low
program costs scenario is equal to the median levelized cost of saved energy ($0.06/kWh) for utility
residential whole home or direct install program in the U.S. (LBNL, 2014).15
Utility average cost of heating savings would be $2.17/therm for the low program costs scenario and
$3.79/therm for the high program costs scenario. This average cost per them savings from a TCC
15
LBNL based this estimate on an analysis of 19 residential whole home/direct install utility electricity efficiency
programs. See LBNL (2014), p. 34.
26
thermostat program would exceed the national average cost of lifetime saved energy for residential gas
efficiency programs of $0.32/therm (LBNL, 2014). The utility average cost of therm savings also exceeds
the 2013 average city gate price of natural gas, which ranged from a low of $0.39/therm (Idaho) to a
high of $0.62/therm (Vermont) in the continental U.S. (EIA, 2013). It should be noted, however, that the
cost of therm savings compares unfavorably in part because natural gas costs are at recent historic lows.
Utility average cost of saved energy from TCC thermostats varied significantly by climate zone in
accordance with the estimated annual energy savings. The Hot-Humid ($0.04/kWh) and Mixed-Humid
($0.04/kWh) climate zones) had the lowest cost of saved energy for the low program costs scenario.
This cost of saved energy compares favorably with the national median levelized cost of saved energy
($0.06/kWh) for utility residential whole home or direct install program (LBNL, 2014). The Very
Cold/Cold ($0.12/kWh) and Hot-Dry/Mixed-Dry ($0.30/kWh) climate zones had higher utility average
cost of saved electricity.
Utility average cost of therm savings was lowest in the Hot-Dry/Mixed-Dry ($1.12/therm) and HotHumid ($1.07/therm) climate zones. Nevertheless, these costs of saved energy still exceeded the
national average cost of lifetime saved energy for residential gas efficiency programs.
While this analysis suggests a utility’s cost of achieving energy savings with Honeywell TCC thermostats,
it does not account for all of the utility’s benefits. The estimates of costs of saved energy do not account
for all of the benefits to a utility that wants to use the thermostats to achieve space-heating and spacecooling energy savings. Also, electric utilities wanting to manage system peak loads can use TCC
thermostats to control residential or small commercial customer space-conditioning loads. Utilities
wanting both energy and peak demand savings will want to consider both potential benefits.
27
Conclusions
Connected thermostats may reduce energy use for home space conditioning. Mobile connectivity
reduces the cost of control for home heating and cooling, and helps users better maintain their
preferred interior temperatures. This reduction in the cost of control may result in energy savings.
In this study, Cadmus estimated energy savings from Honeywell TCC thermostats. This required
analyzing UI data for approximately 1,800 homes with TCC thermostats and comparing average
temperature set points of thermostats in those homes to self-reported thermostat set points for homes
in the 2009 RECS. Cadmus then estimated energy savings for space conditioning as a function of the
difference in average temperature set points between TCC thermostat homes and RECS homes.
This study did not consider the potential benefits to utilities of using Honeywell TCC thermostats to
manage residential space-conditioning loads to obtain peak-demand savings. Honeywell is running
several pilot studies to evaluate the thermostats’ peak demand savings.
Summary of Main Findings
Overall, Cadmus’ analysis suggests that Honeywell TCC thermostats purchased through retail channels
or space-conditioning contractors saved significant energy for the average adopter and adoption proved
highly cost-effective in many U.S. climate zones.
The energy savings analysis resulted in the following specific findings:

On average, Honeywell TCC thermostats would save about 5% of energy use for home space
heating and 19% of energy use for home cooling during a normal weather year. In total, TCC
thermostats would save about 7% of energy use for heating and cooling.

Honeywell TCC thermostats would save about $25 per home per year in space heating energy
costs and $91 per home per year in space cooling energy costs during a normal weather year.
Total energy cost savings would be $116 per home per year.

Despite small sample sizes for some climate zones, analysis suggests energy and energy cost
savings vary significantly between zones. Savings depend on zone-specific demand for heating
or cooling and the impact of Honeywell TCC thermostats on temperature set points.

The Hot-Humid and Hot-Dry/Mixed-Dry climate zones offer the greatest heating energy savings
and energy cost savings. Homes without connected thermostats in these zones have the highest
average heating temperature set points and, therefore, some of the greatest potential for
energy savings. Estimated space-heating energy cost savings in these regions would be,
respectively, $70 and $39 per home per year.

The Hot-Humid and Mixed-Humid climate zones offered the greatest cooling energy savings and
energy cost savings. As some of warmest and most humid zones in the United States, they offer
the greatest demand for air conditioning. Estimated space-cooling energy cost savings in these
regions would be, respectively, $172 and $121 per home per year.
28

Connected thermostats proved very cost-effective for homeowners in many climate zones. In
the Hot-Humid and Mixed-Humid climate zones, annual energy cost savings would cover or
almost cover the incremental cost of a Honeywell TCC thermostat. Homes in the Mixed-Dry/HotDry and Very Cold/Cold climate zones would achieve a positive return on their investment after
between one and two years.

The average cost of saved energy for a Honeywell TCC thermostat utility direct-install program
would be $0.06 per kWh, which equals the median levelized cost of saved energy ($0.06/kWh)
for utility residential whole home or direct install program in the U.S. (LBNL, 2014).
Future Research
In performing this research, Cadmus identified a number of questions for future research:

This analysis pertains to very early adopters of Honeywell TCC thermostats. Do subsequent
adopters experience the same, lower, or higher energy savings?

Energy savings and energy cost savings estimates differ substantially between climate zones
(though based on relatively small analysis sample sizes). Do such differences between climate
zones remain among more recent adopters?

How do adopters achieve energy savings? Adopters of TCC thermostats could have saved energy
by reducing the intensity of space conditioning when their heating or cooling system were on or
by reducing the number of days or hours that space-conditioning units were switched to on.

How persistent are energy savings from TCC thermostats? Do savings increase, decrease, or stay
the same with time since adoption?
Cadmus is performing a second national impact study to answer these questions. The study will analyze
UI data from 2013 for a very large number of homes with Honeywell TCC thermostats. Cadmus will
update this study’s results and provide a more comprehensive set of findings about energy savings from
Honeywell connected thermostats.
29
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