I am getting a new central A/C unit that has seen better days. It's 15+years old, and it finally died. I was told they have to replace somethingabove the furnace (the condesor?). While they are here working on myfurnace, should I just get a new furnace too??I have a Lennox furnace that is still working, but it's 9+ years old.Manufactured in early1993.Of course, they are offering me a package deal to also replace the furnaceif I want. Initially I said no, but I have no idea the average lifeexpectancy of an average furnace. If they only last 12 years (on average),I hate to have them back out in a year or so.Looking for advice for anyone that was in my situation.......

If it 80% or less efficent and you have a long heating season, run thenumbers. to see what you will save with a 94%. Otherwise no I wouldnt

Should I replace a 9 year old furnace?

Nov 19, 2003 26 Replies

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mark Ransley 22 years ago

90% vs 50 = 40% savings, . One gas one is 96.6% , many are 94 and 95%. And a variable speed blower may save 75% on your old units blower KWH cost. Not knowing how much it runs It cant be figured , but it could easily save 15$ a month in electric costs and boost SEER for central air by 1 seer. Plus not pullng inside air for combustion helps. Your unit wasnt designed for efficency. Nothing was then.

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Ermalina 22 years ago

If H is the amount of heat needed in a given situation, for example, to heat your house this Winter:

Let x = the amount of fuel it takes to produce H by a 50% efficient furnace y = the amount of fuel it takes to produce H by a 90% efficient furnace

Therefore:

.50x = .90y

So, y = (5/9)x = .56x

In other words, a 90% efficient furnace uses only 56% of the fuel used by a 50% efficient furnace to produce the same amount of heat. So, a 90% efficient furnace (THEORETICALLY) should save 44% in fuel. However, I suppose YMMV.

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Ermalina 22 years ago

BTW, we live in the Midwest (COLD winters) and have a 25 year-old Amana Air Command that is going strong and will not be replaced until it dies or develops serious probs. The folks (a family business which has been around for 3 generations) who maintain it, and who will be doing the installation of the new one which replaces it, agree.

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Stormin Mormonn 22 years ago

About 40%.

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CBHvac 22 years ago

Give or take your situation, and usage, between 55%% to 62% less..Installed correctly, depending on your fuel costs not, it could, theoretically, have a tremendous payback. Altho, I dont sell on the payback theory, since you have to pay to get it installed, and it does cost every time you turn it on.

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CBHvac 22 years ago

The design, and the final AFUE rating.

Both. Todays furnace isnt the one that you had when you grew up...(well..for some it might still be..LOL) but seriously, huge design changes, computer controls, secondary heat exchangers, better blowers...it all adds up.

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CBHvac 22 years ago

What formula you use to get that wrong number?

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