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Contractor doesn't want to install 90%AFUE unit in Attic Space

Is it true that it is problematic installing 90% AFUE furnaces in the attic space? I am building a 3200 sq ft home in NC and my contractor says that putting higher than a 80% AFUE furnace in the attic could lead to water problems down the road (if drain stops up and drain pan were to also stop up). He says the 90% units withdraw so much water they can be a problem down the road. We'll have a split system: 80,000 BTU Lennox Gas Furnace 2.5 Ton AC Unit upstairs and a 80,000BTU 90% Gas furnace downstairs with a 3 TOn AC Unit. Is this him not wanting to warranty an installation in the attic space? I'd prefer the higher efficiency unit if possible. Thoughts?
 

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Are you in Charlotte? As to drainage that is why you have two drains with one being a back-up.

Here is a quick way to check. Call three HVAC installation companies and ask them the same question. Just ask them about the difference between the 80% and 90% furnace and the water. Yellow pages work great. This will almost all the time show a pattern. If you need call 5.

Of the wall, I have never heard this. That is why it is so important to check your drain lines a couple times a year.
 

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Since 90% furnaces expel water as a by product due to their combustion process, it isn't an unreasonable fear of having a drain line freeze in an unconditioned attic and cause water damage. Even with a condensate pump, you run the risk of the outlet still freezing causing it to overflow into your attic/ceilings. Think about how a water faucet freezes up that has been left on to trickle, the drain will do the same. And if you do happen to catch it frozen up (before it overflows into the attic), what do you do then? Not run your furnace till it warms up above freezing? Tear apart the drain and try to clear the ice and hope it doesn't do it again?
 

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Now that you explain it like that "DOC", I'm feeling much better. No one else mentioned freezing. So do you reccomend no more than an 80%?
 

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I wouldn't in an attic like that. Even here in Kansas where we don't always have "cold" winters, you would be hard pressed to find anyone who will put a 90% in an attic because of the liability. Just isn't worth the risk for the homeowner or the contractor. I am sure there are some installed in attics around here but most folks I have met do not want to be the "What if...." person nor does my insurance want me to put them in that position.
 

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What is the difference in effiency between the two furnaces? And just curious what is the cost difference? Just pick any two mansufacturers you like to do a simple check.

I'm just curious myself. Explanations are great. It's those types that help with the consumers.

Thanks
 

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Well the difference is pretty easy. You have an 80% which in its simplest terms means you get .80 cents worth of heat out of every dollar you spend on gas. The 90%+ means you get .90+ cents (depends on its efficiency there are some that are up to 96% efficient) worth of heat out of every dollar. So you can have a minimum of 10% difference between the two types. 80% vent with standard metal double wall flue pipe where as the 90%+ take so much heat they can vent with PVC (exhaust gas averages about 98-103 degrees). As for price difference, you can average at least $800.00 more not including other things such as variable speed motors, modulating gas valves, and two stage gas valves. Payback is tricky to figure as you have to figure how much time you expect to be in your home (will you ever see the extra cost) as well as guessing what gas rates have done. On average in our area, you can figure a 5-7 yr. payback on upgrading to 90%+. But again, if gas rates bottom out, a series of warmer than normal winters, etc. can increase the amount of time. On the flip side, cold winters and gas rates increasing radically (like they have done past 4 yrs.) can decrease the amount of time due to the increased savings.
 
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