Sizing quesion

[mdabisch]

Hi all,

I've decided on a contractor and a furnace. They had quoted me an 80K BTU in/72K BTU out system (90% efficient).

I had gotten estimates from several contractors and the size was all over the board. They were all 'rules of thumb' guesses. So I had my selected contractor do heat loss (manual j) calc on the house. It came out to be ~ 44K BTU. I was overwhelmed with how low it is.

I live in the Chicago area and the house is a 1.5 story 1926 craftsman (1500 SF) with a full heated basement. No wall insulation (for the most part) but 15 inches in the attic. And almost all new double pane windows on the house. Does the heat loss calc seem like it is correct? The current furnance I have is a 110K BTU in/77K BTU out (70% efficient). It just seems like such a difference to go all of the way down to a 54K BTU out unit. I guess I'm looking for some reassurance.

I'm thinking I should go with the smaller 60K BTU in/54K BTU out system. That still gives me a 25% percent safety factor according to the calc!! I like the two-stage furnace but to get anything out of it I would definitly have to go with the smaller. Otherwise if I went with the 80K BTU unit, it would only run on the first stage 97% of the time I think.

Thanks in advance. This forum has been very helpful in my search.

- Mike

[BaldLoonie]

I would certainly not use the 80,000 BTU furnace. Even the 60K is overkill but better than the even bigger one. There are brands at 45,000-50,000. You can get a 60K 2 stage furnace as well. A-S/Trane's would then be 36,000 BTU input on low fire.

Friend built a new house, 1500 sq ft on 2 floors plus 750 sq ft basement, 3 zone. Well built. I had the panel set that unless all 3 zones called, would only run on low. Since the basement was unfinished, it wasn't heated. So basically that 1500 sq ft place heated on 36,000 input all winter last year down to 0 out, 70+ in.

[mayguy]

Did you express the concern of the numbers? Asked for a printout of the report, and see if any area/rooms been left out?

You can down load a home owner's version above for $50, and compair.

I have a 1,700 sq ft '68 Split home, and the old furnace was 115,000, and replaced with two stage 60,000 and it ran just fine with our Minnesota winter.