Furnace in unconditioned attic


Old 12-08-10, 08:01 PM
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Furnace in unconditioned attic

I am looking at replacing my existing hot-air furnace that sits in the attic and is about 83% efficient. I have spoken to two contractors. One says that he would install a 95% efficiency unit (Goodman) and the other says that he can't go over 80% (Carrier unit) since it's in the attic and I will have problems.

The 95% contractor seems very knowledgeable. He says that the new unit would be sealed, he would vent it directly through the roof above and he would put insulation around the unit, just in case. He said he would re-do my duct work which is all flex and badly done and he would relocate the registers and returns etc and put bigger ones where needed. He says my gas bill would be cut in half and my house would be much better heated.

The second guy wants to, essentially do a furnace swap. He says he would install a lower efficiency furnace and simplify the ducts a little by making them shorter and untangled them where needed.

I am not sure which way to go. My house is about 40 years old, built on a slab and very badly heated. Registers are small and the air flow is weak. My feeling is that more than the energy efficiency of the furnace, the ductwork would make a bigger difference. So I want to go with the 95% contractor but I am not sure if his advice on the energy efficiency is going to cause more problems in the long run. Should I ask him to do the rest and install an 80% furnace?

Any comments would be appreciated.
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Old 12-09-10, 04:45 PM
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big problem...in the attic

if you live a a cold northern climate,it is not a good idea to install a 90 plus furnace in the attic...you have to get rid of the furnace condensate.....drain it ,pump it,etc.....if it gets so cold in the space...furnace trips out,you are in trouble. it could be done,but you are muck better off putting in an 8- percent where you do not have to worry about the condensate...
Old 12-09-10, 04:53 PM
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No way, no how would I put a 90+ in an unconditioned space where the temps will be below freezing. I've seen more than one secondary heat exchanger freeze & split. Some manufacturers state specificly in their installation instructions that the furnace is NOT to be installed in an area where temps drop below freezing.
Old 12-10-10, 04:48 AM
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Thank you

Thanks Gentlemen. Your comments help. I will talk to the contractor again.
Old 12-10-10, 09:38 AM
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Not sure how cold your winter can be, but here in Minnesota, a risk that we DO NOT take (and very very rare we have furnace in the attic here anyway), even tho some company say "do this and that" but it's a gamble, and lot of time people don't poke up into the attic to check on things.

I'd put the money into a two stage variable speed 80% furnace for the best comfort, and make sure get a two stage stat with it.
Old 12-10-10, 12:00 PM
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go with the 95% contractor but tell him to go with a standard 80, the other guy sounds like an idiot.

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