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  1. #1
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178

    Difference between 80% and 95% gas furnace

    Could someone please explain the difference between an 80% and 95% gas furnace? While I know the difference relating to efficiency, I'm curious how different they are mechanically, such as why doe the 80% can use a regular chimney and the 95 only needs pvc. Does the 80% run that much hotter?

    Also, if the 95 is so much better why would anyone even want the 80%.

  2. #2
    Join Date
    Aug 2012
    Location
    North Dakota
    Posts
    518
    well the 90% plus furnace is known as a condensing furnace (ie more heat is removed until the products of combustion are allowed to reach their due point) thus commanding the pvc venting," Water" containing acid
    As far as why an 80% unit some reasons may be venting issues, though it's generally a $ thing

  3. #3
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
    Posts
    3,512
    the 90+ furnaces are generally made of stainless steel to survive the acid condensation collecting in points of the furnace.
    dollar for dollar, the 80% equipment can be a better value if you already have the venting in place for it. no modifications are needed for drain provisions, there's no freeze danger if installed in non conditioned space, and they can be quieter. so on a budget, the 80% can be a bargain, with only a small loss in efficiency.
    I generally install 90% equipment, because there are more options with installation, and it's a fuel savings that looks good on the quote.
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  4. #4
    Join Date
    Jan 2012
    Location
    Arrowhead Stadium
    Posts
    510
    90% has a secondary heat exchanger dropping exhaust temp from around 400 to 100 degrees. more heat inside,less outside.

  5. #5
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,428
    With an 80% furnace, 20% of the heat created goes up the flue pipe. This waste heat is still pretty hot, too hot for pvc pipe.

    A higher efficient furnace basically takes your flue pipe and routes it a few more times through the airstream so that more of the heat goes into your home, and less is wasted through your chimney. The problem is that the flue gas actually has a lot of acidic moisture contained in it. As long as it is kept nice and hot, it will be carried out your chimney pipe and won't cause any problems. As the flue gas gets cooler (i.e.. a more efficient furnace), this acidic moisture will begin to condense out of the exhaust gas. That means that the furnace and it's flue pipe need to be designed differently, so that the parts that are in contact with this corrosive acid water will be able to withstand it.

  6. #6
    Join Date
    Dec 2005
    Location
    Cleveland, OH
    Posts
    2,757

    Difference between 80% and 95% gas furnace

    About 15%
    Last edited by dougfamous; 12-13-2013 at 06:42 PM.
    Good? Bad? I'm the guy with the gun.

  7. #7
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,505
    In southern climates and areas with cheap gas rates, payback time may be too long to justify the 95% furnace vs. 80%.

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