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Old 09-28-2009, 06:15 PM   #1
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Furnace sizing for condo


I have an approx 950 sq ft condo and am currently looking to replace my 25 year old furnace. I am looking to put in a new 95% furnace and have gotten 4 quotes. They have quoted me for furnaces ranging from 40,000 BTU to 70,000 BTU.

I would like to go with the quote I got on a Bryant 355CAV 60,000 BTU, but I am worried that the 60,000 BTU is going to be too much. The furnace has a variable speed fan and multi-stage burner and the salesman assured me that with those features the 60,000 BTU would be fine because it would pretty much just run on lower settings (haven't been able to find any specific technical information about what heat outputs it can actually run at).

Luxaire has a 40,000 BTU 95% furnace that I got a quote on, but I am a bit leery of the brand.

If this helps...I live in an area with approx 6500 annual heating degree days. We have probably about the equivalent of 6 windows and are pretty well insulated. We are an upstairs corner unit with one unit below us, so we get some heat from that unit.

Any input would be very much appreciated.

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Old 09-28-2009, 07:23 PM   #2
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Furnace sizing for condo


How did your contractor come up with furnace size? typically a heat loss calc should be preformed. Brand really does not matter if installed and sized correctly.Condos have there buildings attached reducing some of the load.

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Old 09-28-2009, 07:36 PM   #3
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Furnace sizing for condo


I live in an older 2 story house 1650 sq ft & my load calc came out as 68,000 BTU

Newer windows & some updated insulation on the original house
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Old 09-28-2009, 07:39 PM   #4
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Furnace sizing for condo


No one has done a sizing calculation. The current furnace is 50,000 BTU and probably around 60% efficient, which gives me around 30,000 BTU actual output. That was definitely sufficient last winter in terms of keeping the place warm enough. A 40,000 BTU 95% efficient furnace would give me a 38,000 BTU max output. So a 40,000 BTU seems pretty reasonable to me. And it seems as if 40,000 BTU is about as small as they come.

Brand must matter somewhat, because I have heard bad things about Luxaire.
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Old 09-28-2009, 07:58 PM   #5
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Furnace sizing for condo


I also got a quote on a 95.5% 40,000 BTU Bryant (350AAV), but it only has a single speed blower and I believe just a single stage burner.
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Old 09-28-2009, 08:36 PM   #6
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Furnace sizing for condo


Quote:
Originally Posted by sambisu View Post
Brand must matter somewhat, because I have heard bad things about Luxaire.
Luxaire is York is Coleman. I would not waste too many brain cells vacillating over brand. A good installation will trump a brand difference every time.

As far as size is concerned, any of the 95% 2 stage, variable speed furnaces on the market will be fine in the 40,000 - 50,000 btu range. you contractor is correct that with your sq ft it will probably spend most of its life on the first stage of heat. First stage of heat will hover around the 60-70% range depending on make and model.

A heat load is usually a good idea, but in your case with 950 sq ft and a reasonable insulation factor, you are basically narrowed down to the smallest furnaces available, so a heat load is really not the end all here.
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Old 09-28-2009, 08:45 PM   #7
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Furnace sizing for condo


Thanks for the replies...I was actually able to track down some specific information on the stages of the Bryant 355CAV.

It has three settings:
Low - 8,000 BTU/burner
Med - 13,000 BTU/burner
High - 20,000 BTU/burner

So for the 60,000 BTU furnace, that would allow it to operate at 24,000 BTU, 39,000 BTU and 60,000 BTU. In comparison to a 40,000 BTU single stage, this definitely seems like a better option.
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Old 09-29-2009, 04:41 AM   #8
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Furnace sizing for condo


You can find bad things being said about any brand..
Luxaire is a good brand.

Might want to get a quote on a Luxaire mod. It can fire as low as 20,670 BTUs. And since it really modulates instead of being just 3 stages like the Bryant. It can match your heat loss much closer.

Are you also getting the Infinity/evolution control with that Bryant. Or are they just going to set it up on a furnace board?

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