1/19/2012

1

Diagnostics for Mobile Homes: HVACAdam Harris – NYSWDAWade Thompson - IWTC

Objectives

• Identify different types of HVAC used in mobile homes• Provide an overview of duct systems• Demonstrate various tests

1/19/2012

2

Mobile Home HVAC Units• Specifically designed for use

i bil h

FlueFlue

in mobile homes• Usually live in a closet• Sealed combustion with

dedicated combustion air inlets• Short metal chimney design• Compact interchangeable burners

Heat ExchangerHeat Exchanger

BlowerBlower

Combustion AirCombustion Air• “Down-Flow” air distribution system• Ducts located in the belly cavity

Combustion AirCombustion Air

BurnerBurner

3

Photo courtesy of WV GOEO

MOBILE HOME HEATING SYSTEMS

Furnace Main DuctRegisters

Return Air

4

1/19/2012

3

Lengthwise Floor Joist System

Crosswise Floor Joist System

The problem with Ducts

New factory installation includes duct tape

New factory installation includes duct tape

Failed duct tapeFailed duct tape

Photos courtesy of PA WTC

Failed duct tapeFailed duct tape

1/19/2012

4

Furnace base

Bottom of the heat exchangerBottom of the

heat exchanger

Smashed bootSmashed boot

Photo courtesy of PA WTC

No heat? No wonder!

Main ductMain duct

1/19/2012

5

Combustion Air Intake

Exhaust

Supply Air Fan

Return Air Intake

G Oil B

9

Gas or Oil Burner

Supply Air Duct

Flue Vent Pipe for Exhaust Air and Gases (Hot)

Entry Pipe for Combustion Air (Cool)

Return Air Intake

Blower

Heat Exchanger

Combustion ChamberChamber

Air Conditioner Coil CabinetTo Heating Ducts

10

1/19/2012

6

Fresh Air InletFresh Air InletFresh Air InletFresh Air Inlet

11

Photos courtesy of PA WTC

Check clearance to combustibles

12

Photos courtesy of Tony Gill

1/19/2012

7

Photos courtesy of PA WTC

Oil Burner and Combustion Air Inlet

Furnace Testing Methods

Test for:• Steady state efficiency• Fuel leaks• Cracked heat exchanger

C b id l l• Carbon monoxide levels• Smoke (oil)• Temperature rise

14

1/19/2012

8

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 • Flue gas temperatures • Oxygen (O2) or Carbon Dioxide (CO2)• Carbon Monoxide (CO) levels• Draft• SSE

Test HoleTest Hole

16

Single wall flue

1/19/2012

9

Sealed combustion testing locationSealed 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

Test HoleTest Hole

Apply high temperature sealant to the inner hole

• Apply sealant to outer hole and cover with aluminum tape

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

1/19/2012

10

Remove and clean the blower.19

Photo courtesy of PA WTC

• 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 locationsthe temperature rise

• Should be between 40˚ and 70˚ or no greater than the manufacturer’s specs

Temp ProbeTemp Probe

• Excessive temperature rise indicates • Dirty filter• Blockages• Insufficient return or supply duct

cross sectional area• Low fan speed or dirty fan

Temp ProbeTemp Probe

20

1/19/2012

11

• Verify fan operating temperaturesHigh Limit set at factory (200˚)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

Fan-on/Fan-off test location

the supply plenumTemp ProbeTemp Probe

21

Inspect for cracks & corrosion

1/19/2012

12

Heat exchanger test methods:• Look for flame damaged areas on the heat 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 onblower turns on.• Look for flame damaged areas on the heat

exchanger.

23

A furnace should be replaced if any of the following y gconditions exist:

• The furnace has a cracked heat exchanger

• Repair and retrofit exceeds half the cost of the replacement cost

24

• The furnace is not operating or repairable

Photo courtesy of WV GOEO

1/19/2012

13

• 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 furnacethe 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 homesReplace 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