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 1
Mobile Home HVAC Units Specifically designed for use in mobile homes Usually live in a closet Sealed combustion with dedicated combustion air inlets Short metal chimney design Compact interchangeable burners Down-Flow air distribution system Ducts located in the belly cavity Flue Heat Exchanger Combustion Air Blower Burner Photo courtesy of WV GOEO 3 MOBILE HOME HEATING SYSTEMS Return Air Registers Furnace Main Duct 4 2
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 3
Furnace base Bottom of the heat exchanger Smashed boot Main duct Photo courtesy of PA WTC No heat? No wonder! 4
Exhaust Combustion Air Intake Supply Air Fan Return Air Intake Gas or Oil Burner Supply Air Duct 9 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 10 5
Fresh Air Inlet Fresh Air Inlet Photos courtesy of PA WTC 11 Photos courtesy of Tony Gill Check clearance to combustibles 12 6
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 monoxide levelsl Smoke (oil) Temperature rise 14 7
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 (O 2 ) or Carbon Dioxide (CO 2 ) Carbon Monoxide (CO) levels Draft SSE Test Hole Single wall flue 16 8
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 18 9
Photo courtesy of PA WTC Remove and clean the blower. 19 Place a thermometer probe into the return plenum and another one in the closest supply duct. Record the temperatures Temperature rise Calculate the difference to determine test locations the temperature rise Should be between 40 and 70 or no greater than the manufacturer s specs Excessive temperature rise indicates Dirty filter Blockages Insufficient return or supply duct cross sectional area Low fan speed or dirty fan Temp Probe Temp Probe 20 10
Verify fan operating temperatures High Limit set at factory (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 Temp Probe Fan-on/Fan-off test location 21 Inspect for cracks & corrosion 11
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. Look for flame damaged areas on the heat exchanger. 23 A furnace should be replaced if any of the following 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 24 12
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 25 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. 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. 26 13