Pros and Cons of furnace features

[Whybwawian]

I have a a small (980 sq ft) one story house on a slab, in Michigan. I also have a small budget, and a house that isn't worth much. I am replacing a furnace that is at least 40 years old. My contractor has given me two quotes that are within my price range, one for an 80% efficient, two-stage, variable speed furnace, and one for a 95% efficient single-stage furnace. Aside from the gas savings with the 95% furnace, how do these options compare in terms of comfort, quiet, repair expense? Any other considerations?

[BaldLoonie]

What size? Dealers tend to way oversize in little houses. The 2 stage variable speed has the comfort advantage, the 95% will cost less to run though in a tiny house, that doesn't make a lot of difference. Your house is the same size as mine.

[Whybwawian]

Both are 60,000 btu furnaces. The 2 stage has max output of 31,200 in stage 1, 48,000 in stage 2. Single stage has max output of 57,000.
Load calc showed I required 33000.

[NCHeat]

Ask about a 40K 95%. Seems that would fit your needs quite well. 2 stage is nice but with a home that small, not sure whether it's a real benefit. IMO

[BaldLoonie]

Yup, dealers like to oversize small homes. Get the 40K in a 95%. If you go with an 80%, then the 60K wouldn't be as far out of line but still big.

[Whybwawian]

Thanks - I'll ask about the 40K. But if it's just a single stage, will I be unhappy?

[carmon]

depends on the brand and installation..... some are noisier than others.... a poor install will certainly make you unhappy

[tedkidd]

You have/want AC? House that small might be ideal for ducted or ductless minisplit heat pumps.

[Whybwawian]

No AC, and I don't really want it.

So how do BTUs translate into actual gas usage? Is it possible that the two-stage furnace, if it runs most of the time in stage 1, will actually use less gas than the one stage, more efficient furnace?

[tedkidd]

No AC, and I don't really want it.

So how do BTUs translate into actual gas usage? Is it possible that the two-stage furnace, if it runs most of the time in stage 1, will actually use less gas than the one stage, more efficient furnace?

You're worried about energy costs? House that small might be ideal for ducted or ductless minisplit heat pumps.

[martyinlincoln]

No AC, and I don't really want it.

So how do BTUs translate into actual gas usage? Is it possible that the two-stage furnace, if it runs most of the time in stage 1, will actually use less gas than the one stage, more efficient furnace?

There's roughly 1000 BTU in a cubic foot of gas. Half the BTU but running twice as long uses the same amount of gas. It's about comfort. Longer run times equals steady temps instead of the on/off heat up/cool down cycle.

My house is the same size and construction. Our design temp is -2 and we went with a two stage 95% furnace that has 44K Btu on high fire. It only goes on high fire when outdoor temps fall in the -10 range and below. The 2 stage 95% is only a little more than the single stage,very little, so IMO go for a high eff. two stage.

[BaldLoonie]

You can get a 2 stage variable speed blower in small models as well. Rheem has it in the -04 which is 45K.

But if you have a small budget and a house that isn't worth much, bare bones single stage 95 probably makes the most sense.

[Whybwawian]

Does anybody make a 40K 2-stage downflow furnace? Ducts are in the slab

[Kevin Weaver]

I would chose an 80% eff. WITH variable speed over a 95% with a standard motor. The variable speed furnace has lots of advantages, 1 being it makes the a/c work about 15% better.

[BaldLoonie]

Rheem, Allied (guessing Lennox too), ICP, (guessing Carrier too), UPG (York brands) all have 40-45K 95% 2 stage variable speed.