How do I properly match a new gas furnace to an existing A/C unit?
January 17, 2010 8:02 AM Subscribe
HVAC befuddlement - Does anyone understand the consequences of having a blower on your furnace that is undersized for the A/C unit you have?
posted by chinston to home & garden (12 answers total)
I live in a house with a gas furnace that needs to be replaced (busted heat exchanger, leaking carbon monoxide). The furnace is way overpowered for the size of the house -- 130,000 btu whereas our needs are about 80,000 btu. An 80k btu furnace would give us a "3 ton blower," but because our current A/C unit is 4 tons, I'm told, this will be a mismatch.
What is confusing me is the precise consequences of the mismatch. One contractor tells me that the problem will just be inefficiency, because the blower won't be big enough to move the cold air around. The other contractor, though, tells me the consequences will be much worse -- "freeze up" of the A/C unit. So the second contractor's proposal is to get a 100k btu furnace with a 4-ton blower which will avoid that problem, even if the furnace will be a little too big for our house.
The thing is, we don't use the A/C more than about a week out of each year, versus the furnace for several months in the winter. So it's more important to me to have an efficient furnace. But I don't want to risk "freezing up" the A/C.
Has anyone encountered similar problems in trying to match a furnace and A/C unit? What did you do?