Furnace/duct problem

[earache]

My mother in law just bought an older MH ('72). The furnace was replaced in '98 with a Coleman... don't know the model. She's been having really high PGE bills and thinks a lot of it is due to heating (she likes a warm house). Just last week the furnace started acting up... it just wouldn't fire up. The primary ignition worked fine but the secondary would light and then shut down a few seconds later. It was a sporadic problem and would usually resolve itself after turning the thermostat on/off a couple of times. So this problem persisted for several days and she called her home warranty company to send someone out.

The HVAC guy comes out and determines that there are two contributing issues. First, the return air duct is just sucking air from the crawlspace, not from the return air vents. Second, the ignition air vent is not pulling air entirely from the roof vent, but from the attic space as well. The insurance company won't cover the repairs because they say it was a "pre-existing" condition and won't revisit her furnace startup problem until we get everything else fixed. So question for the experts... How are return air ducts usually run in MH's? I could find no sign of any traditional duct work while I was under the house. Most of the underside is sealed up, but I can plainly see the furnace return through a large hole in the membrane. I didn't see any flex-tube ducting at all. Do the metal beams running the length of the home and the membrane act as the duct??? As for the ignition air vent, is it ok to open up into the attic space? Any help is greatly appreciated.

Thanks,
Eric

[Robert]

Hi Eric,


The return air is either throughout the home itself and coming into furnace through louvered door panel or through floor registers and the underbelly acts as a return duct pathway.


No, roof-jack should not be open to attic cavity. It should be double walled, sealed combustion/venting with outer and inner piping.


Make sure it is not separated and allowing vented gas to enter combustion air and return to furnace.



If possible, fire the home warranty company and never go that route again. Huge waste of time and money. IMHO.


Thanks,

Robert

[earache]

Thanks for the info Robert.

So let me get this straight, if I reseal the underbelly membrane then technically I should solve the return air problem, correct? There are numerous holes in the underbelly where plumbing repairs have been made. We have 3 floor registers in the unit which are basically just open to the underbelly airspace. Do you have a recommended method for sealing? I don't recognize the underbelly membrane material at all.

As for the vent, it's definitely wide open and not sealed. I guess when they put on the new roof they just cut the pipes back and never bothered to replace/extend them to the new roof line.

This is starting to make sense now. Thanks very much.

Eric

[Robert]

Hi Eric,

Are the supply registers in the ceiling ?


Go to blue toolbar above and click on Books & Parts, then click on Belly Repair link for our belly repair supplies.


Is the furnace a Coleman or Nordyne ?


Thanks,
Robert

[earache]

Yes, the supply vents are in the ceiling. Furnace is a Coleman, but I don't know what model. Thanks for the belly repair link.

[Robert]

Hi Eric,

Floor registers open to belly area with ceiling supply registers means an upflow furnace and the belly area is the return duct.


You're very welcome on the belly link.


For roof-jack, measure from top of furnace to the roof (not ceiling) and then select a roof-jack that falls close to middle of that range.


Also get hydroment sealant and seal flashing and swivel joints good.


They can be seen and ordered through PayPal from here :

http://www.mobilehomerepair.com/ColemanChimneys.html



Thanks,
Robert