Diagnostics For Mobile Homes

1/19/2012
Diagnostics for Mobile Homes: HVAC
Adam Harris – NYSWDA
Wade Thompson - IWTC
Objectives
• Identify different types of HVAC used in mobile homes
• Provide an overview of duct systems
• Demonstrate various tests
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Mobile Home HVAC Units
Flue
• Specifically designed for use
i mobile
bil hhomes
in
• Usually live in a closet
Heat Exchanger
• Sealed combustion with
dedicated combustion air inlets
Blower
• Short metal chimney design
• Compact interchangeable burners
• “Down-Flow” air distribution system
Combustion Air
• Ducts located in the belly cavity
Burner
Photo courtesy of WV GOEO
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MOBILE HOME HEATING SYSTEMS
Return
Air
Registers
Furnace
Main Duct
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Lengthwise Floor Joist System
Crosswise Floor Joist System
The problem with Ducts
New factory installation
includes duct tape
Failed duct tape
Photos courtesy of PA WTC
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Furnace
base
Bottom of the
heat exchanger
Smashed boot
Main duct
Photo courtesy of PA WTC
No heat? No wonder!
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Exhaust
Combustion Air Intake
Supply Air Fan
Return Air Intake
G or Oil Burner
Gas
B
Supply Air Duct
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Entry Pipe for
Combustion Air (Cool)
Flue Vent Pipe for
Exhaust Air and Gases
(Hot)
Blower
Return Air Intake
Heat Exchanger
Combustion
Chamber
To Heating Ducts
Air Conditioner
Coil Cabinet
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Fresh Air Inlet
Fresh Air Inlet
Photos courtesy of PA WTC
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Photos courtesy of Tony Gill
Check clearance to combustibles
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Photos courtesy of PA WTC
Oil Burner and Combustion Air Inlet
Furnace Testing Methods
Test for:
• Steady state efficiency
• Fuel leaks
• Cracked heat exchanger
• Carbon
C b monoxide
id llevels
l
• Smoke (oil)
• Temperature rise
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Sample location
• Remove paneling from above
appliance to gain access.
• Take flue gas sample from
connector pipe.
Furnaces must be tested to assess:
•
•
•
•
•
Flue gas temperatures
Oxygen (O2) or Carbon Dioxide (CO2)
Carbon Monoxide (CO) levels
Draft
SSE
Test Hole
Single wall flue
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Sealed combustion testing location
• Drill a ¼ inch hole through the outer and
inner sleeves of the chimney flue assembly
• Extract a flue gas sample
• Record the stack temperature
• Test draft
• Enlarge the hole on the outer flue
• Apply high temperature sealant to the inner
hole
• Apply sealant to outer hole and cover with
aluminum tape
Test Hole
Clean & Tune
• Perform SSE testing
• Clean dirty burners
• Clean and adjust blower
• Replace furnace filter and educate clients how to replace
• Fix excessive temperature rise problems
• Check and adjust fan operating temperatures
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Photo courtesy of PA WTC
Remove and clean the blower.
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• Place a thermometer probe into the
return plenum and another one in the
closest supply duct.
• Record the temperatures
• Calculate the difference to determine
the temperature rise
Temperature rise
test locations
• Should be between 40˚ and 70˚ or no
greater than the manufacturer’s specs
Temp Probe
• Excessive temperature rise indicates
• Dirty filter
• Blockages
• Insufficient return or supply duct
cross sectional area
• Low fan speed or dirty fan
Temp Probe
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• Verify fan operating temperatures
High Limit – set at factory (200
(200˚))
Fan-On (100˚ – 120˚)
Fan-Off (90˚ – 100˚)
• Record the temperatures by placing a
thermometer probe
into or the closest register to
the supply plenum
Fan-on/Fan-off
test location
Temp Probe
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Inspect for cracks &
corrosion
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Heat exchanger test methods:
• Look for flame damaged areas on the heat
exchanger.
• Measure flue gas concentration before and
after blower starts.
• There should be no more than 1% oxygen
change when the blower starts.
• Observe change in draft, CO or flame when
blower turns on.
on
• Look for flame damaged areas on the heat
exchanger.
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A furnace should be replaced
if anyy of the following
g
conditions exist:
• The furnace has a cracked
heat exchanger
• Repair and retrofit exceeds half
the cost of the replacement cost
• The furnace is not operating
or repairable
Photo courtesy of WV GOEO
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•
Select a furnace specifically designed for use in
a mobile home
•
Size the furnace to meet the heating load
requirement of the home
•
Note the differences between the old furnace
and the new one
•
Check to see how combustion air is supplied to
the furnace
•
Follow manufacturer’s installation instructions
exactly
•
The chimney assembly and roof jack will often
need to be replaced
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Summary
• Mobile home heating systems are unique compared to those in site built homes.
• Safety and efficiency tests must be performed, employing both visual and
diagnostic tests
• Mobile home furnaces often need to be replaced due to of poor maintenance and
cracked heat exchangers.
homes
• Replace furnaces with models that are approved for use in mobile homes.
• Clean blowers, replace filters and educate clients about the need for routine
maintenance.
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