As a prospective buyer of a replacement gas furnace, I have been reading many of the posts in this forum for several weeks now. I have learned a great deal about a number of things, including what to look for in an installer/vendor.
I have obtained about half a dozen estimates to replace a 23 year old 120,000 BTU Carrier furnace. I live in a 2100 sq ft condominium in a renovated 1920s brick building in the Boston area. Our current furnace works all right, but it has very short cycles and the condo gets a bit cold in between cycles. i am thinking that it may not last much longer and that a 2 stage variable speed model may provide more comfort. Also, we have to go with an 80% model because there is no way to vent the high efficiency furnaces in our building.
Only two of the potential installers have taken measurements of the condo and done heat load calcs. Heat loss was calculated at about 59,000 BTUs by both installers. However,they are each recommending different size units -- and this leads up to my question.
The first installer recommends an 80,000 BTU 2 stage variable speed. The second installer recommends a 100,000 BTU 2 stage variable speed and states that "because of the inherent ductwork a larger blower will be needed."
Now the ducts are quite large, and i cannot afford to change them. So my question is: Is it true that the size of the ductwork determines the size of the furnace -- and that i may have to go with an oversized furnace because of the ductwork??
All the other installers kind of eye-balled the place and then gave me an estimate for a 120,000 BTU furnace, which i assume is oversized. However, this new issue with the size of the ductwork now makes me wonder if they somehow took that into account in staying with a 120,000 unit.
So anyway, i am quite confused, and would appreciate any input on this question!