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  1. #1
    Hey guys (and gals!),

    I'm in southern MI, and leaning strongly towards getting a 90% furnace. I've looked at the bills, and assuming that gas prices keep rising, I think it will pay off.

    I was just wondering if anyone with a 'gut' feeling about 80 vs 90 furnaces in this area would like to chime in?

    Thanks!

  2. #2
    Join Date
    Nov 2004
    Posts
    2,927
    I am not a mathmatician,but...
    I think you will have a 10% lower gas bill
    with a 90% furnace.

  3. #3
    Join Date
    Nov 2004
    Posts
    2,927
    There are other things to consider too.
    Is this planning new construction,or replacing your existing furnace?

  4. #4
    Join Date
    Nov 2004
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    2,927
    .

  5. #5
    Join Date
    Nov 2004
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    Cost of retrofitting a 80% maybe much cheaper than 90%,..maybe the opposite,a 90% maybe easier to install.

  6. #6
    Jacob,
    This is a replacement for a ~30 year old system. I already have quotes and I'm just trying to come to a determination if the extra $ are worth it.

    You mention 10% fuel savings, but I'm thinking that since most 80% furnaces that I've seen are actually 78% and the 90's are 93% or higher, that my fuel savings would be about 14%.

  7. #7
    Join Date
    Nov 2004
    Posts
    2,927
    Originally posted by bubba gump
    You mention 10% fuel savings,
    Yes sir,I was trying to say something like Forrest Gump...make something simple sound genius.

    Again,I have no way of knowing for sure without actually being there.Iwould say this though,if you have the money to go 90+ now,then do it.

    keep reading this site and you will be amazed at what you find.The search function is great.

    Also,make sure you get a furnace size that fits your home.
    "Bigger is not better."

  8. #8
    Join Date
    Mar 2004
    Posts
    1,042
    I vote 90+%, sure bet. 90% is 10% higher than 80%, but the percent difference between the two is 12.5%. 93% should manifest a 16.25% fuel savings over an 80%.

    Make sure to have it configured to get its combustion air from outside; otherwise you're using already-heated air to support your combustion, and exhausting that heat. It takes an extra pipe to do so, but it's a cheap and easy pipe to set up.

    Sizing is critical to get full efficiency out of it. You don't want much excess capacity- which is sad, because in many homes have furnaces double the size of what they need.

    The theoretical maximum efficiency is achieved by running nonstop, well, forever; whatever cycling you have to do starts to cut into that idealized situation. If the unit bigger than it needs to be, it will spend a lot of time starting and stopping, even in really cold weather. You will probably be surprised just how small the right size unit actually is, with respect to both in its rated capacity and its physical dimensions.

  9. #9
    90+ PERIOD... unless you want a dual fuel (heat pump - 90+ back-up) system.

  10. #10
    Thanks everyone, 90% it is!

  11. #11
    Join Date
    Apr 2004
    Location
    Bartlett, IL
    Posts
    6,619
    Actually, your savings should be much higher than 10-15%
    You mentioned your old furnace was 30+ yrs old, that unit is probably 50-60% efficient.

  12. #12
    Join Date
    Apr 2004
    Location
    Bartlett, IL
    Posts
    6,619
    As long as they don't match the size of the new furnace with same size as the old one.

  13. #13
    Join Date
    Jul 2004
    Location
    NW Arkansas
    Posts
    1,288
    Originally posted by bubba gump
    Thanks everyone, 90% it is!
    One thing to consider is the location of the unit. If a 90% unit is installed in an area that can freeze (like an attic or garage) The unit/drain lines can freeze up. This usually causes the homeowner to boil over.

    I have a 90% furnace and I love it. You have made a good choice.

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