Sizing Ductwork for Furnace Replacement

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  #1  
Old 08-25-05, 08:57 AM
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disco
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Sizing Ductwork for Furnace Replacement

I'm getting estimates for a furnace replacement in my small (950 sq. ft, no basement) home.

Recent guy tells me ducts are too small for current furnace (70s era Janitrol- 90.000 BTU input, 75,000 output). Therefore has suggested two stage-two speed furnace. I live in Denver, house is modestly insulated (rock wool in attic) and has single pane windows. Current furnace has always worked just fine and could roast a pig if I turned it up. Replacement more due to age and potential of selling/renting home.

Ducts are standard 7 inch steel. He says "boxes" are too small (assuming the larger collectors near the furnace?).

Anyway, I want to keep costs down, do simple replacement. No way do I want to do ducts.

Advice?

(BTW- I'll have more questions about furnace brands/sizes, install- Should I post here or on Furnace Forum?)
 
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Old 08-26-05, 07:11 PM
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Have you gotten a few other bids? It's hard for us to say if the duct is not sized right with out seeing it. But yeah. lot of the older ducts were not made to move larger amount of air where a newer system does. Do you have A/C?
 
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Old 08-30-05, 10:16 AM
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More bids coming

Thanks, Jay. I am getting two more bids tomorrow, and will know more then.

I do not have, will not get A/C. Evap coolers work fine here in Denver.

Meantime, I'm wondering about sizing the furnace as well. I had bids last year, but decided to ride out one more winter before replacing. I know advice in this forum is to get heat loss calc, but all bids have been for the smallest furnaces anyway (generally 60,000 BTU). Should I get two-stage and/or variable speed fan to ensure house isn't overheated, as well as deal with potentially small ducts?
 
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Old 08-31-05, 04:48 PM
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2-stage works great for comfort.. But it will not "Fix" the duct issues if the duct is too small.
 
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