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  1. #1
    Join Date
    Oct 2005
    Location
    Southern Michigan
    Posts
    24
    Been doing some research/studying, and came across this nugget on my local electric company'a website:

    "The average 80% standard oil or gas furnace lasts 18 years. Most high efficiency 90%+ furnaces only last 12 years due to their longer run times and design characteristics."

    Is this an accurate statement? I had not even considered durability as a consideration, probably because I have had the same furnace for 25 years.

    KJ

  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,723
    good 80% furnace has 20 yr heat exchanger warranty, good 90% is lifetime.

  3. #3
    wow never herd that before, hope its true though, lots of work eventually.

  4. #4
    Join Date
    May 2004
    Location
    Rapid City, SD
    Posts
    7,415
    Everything is going to wear out at one time or another. If you hardly ever use your furnace (say you live down south) it'll last 50 years, but if you live in ND, it might only be 15-20 years.

    The money the 90% would save you over it's live would more than pay for it's replacement I bet.

  5. #5
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    That's a new one too...

    I'd say they will last the same time as long it been taken cared of.

    I agree with the last poster on money saving over time.

  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Originally posted by amickracing
    The money the 90% would save you over it's live would more than pay for it's replacement I bet.
    I'll take you up on that bet. People move every 7 years on average. IF Mr. Jones stays there for twenty years; and if he's lucky enough to not have increased repair costs due to the 90+'s complexity; and if he uses his furnace enough then OK - I'll lose the bet. If so I'll be happy to pay off in 20 years.

  7. #7
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Originally posted by kjones
    Been doing some research/studying, and came across this nugget on my local electric company'a website:
    Which utility's website would that be? I'd be grateful for a link.

  8. #8
    Join Date
    Oct 2005
    Location
    Southern Michigan
    Posts
    24
    Well, this info came from a Michigan utility company(http://my.dteenergy.com/home/savings/heatingFaq.do#q1). So perhaps they have accounted for our winters here, where snowmobiles replace dirt bikes for a couple months... I'm a bit suspicious of them though - in one place they say you can save on A/C using a whole-house fan at night while in another they say you should always keep the windows shut with A/C to keep humidity controlled.

    Not having any cost info available to me yet, I can't do any kind of ROI comparison of 80% amortized over 18 years vs. 90+% amortized over 12 years. But I can estimate the savings difference:

    My gas cost for heating gas last year was about $950 (water heater and base charge was another $180) with my current 30 year old gas burner, and my electric jumps about $50/month for the coldest couple of months too. Shooting from the hip an 80% would save me $300 and the 90% would save me $400. So in 12 years I got $1200 saved up for that new furnace.

    But in 12 years those 80-90% units will be obsoleted by something else. Maybe I should just put in that solar-powered geothermal unit right now and be done with it (how do geothermal costs compare to a 90+% gas system's?)! Only have to go down 20' around here for a well for a lawn irrigation system, anyway...

    KJ

  9. #9
    Join Date
    Mar 2004
    Location
    Gone
    Posts
    5,340
    90% will never pay for the difference over the 80%.

    Actual Btu output of the 95% furnace over the 80% furnace is very little.

    I believe there is a combustion god out here named Jim Davis who has documentation proving this fact already.



  10. #10
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,384
    you are right to be suspicious of that website. many modern single stage 90% furnaces only have one more significant part than their 80% counterparts. that part is the secondary heat exchanger. they are made of stainless steel and last forever (for the most part).

    also long run times are a good thing for equipment. its the starting and stoping of the motors, and heat cycles in the heat exchanger that kill it.

  11. #11
    Originally posted by Irascible
    and if he's lucky enough to not have increased repair costs due to the 90+'s complexity
    Adding a secondary heat exchanger and a drain wouldn't qualify as adding complexity to a unit in my book!

  12. #12
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    "complexity" may be the wrong word. But you know as well as I that 90+ furnaces throw plenty of so called technicians off. And in terms of reliability, any time you add a water circuit to an appliance you end up with more failures. 90+ furances certainly have their place. But it's not all roses.

  13. #13
    Join Date
    Aug 2005
    Location
    iowa
    Posts
    1,649

    Cool

    besides alot of utilities offer rebates for 90 percent furnaces which help offset the costs of the more expensive equipment.

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