The only way to determine the correct system size (and the duct work needed to handle the air flow) is to do a heat gain / loss calculation (AKA "Manual J"). The duct work is sized by a calculation known as "Manual D". Did any of the contractors offer to perform such calculations? If not, call another contractor or two until you get one that sizes by calculation, not by 'rule of thumb'.Originally posted by rickintampa
I've talked to three contractors so far, but their information seems confusing or contradictory. First, all three recommend a new 12 SEER unit. The say that anything rated higher won't save enough electricity to warrant the additional cost. But 12 SEER seems on the low side, especially considering the new government minimums. Also, they differ on size recommendations: One says stay with 2 1/2 ton. He claims that anything larger would necessitate replacing all the duct work. (However, he said this without ever examining the existing ducts.)
It is true that at TECO's current electric rates, anything more than about 13.0 SEER (a Trane XR12 with VS air handler) won't pay for itself during it's expected lifespan. Energy costs may rise in the future, but those are today's calculations.
The quality of the system design and the installation is more important than the brand name. If you are within 1000' of the coastline be sure to look at examples of the brands that you are considering to see if they are rusting after a few years. Basepan rustout has been a real problem on the coast and that is why Trane (and now others) have started using composite basepans.
Either R-22 or R-410a refrigerants will be available in plentiful quantities for the expected life of your unit.