Since your current furnace is a non-variable-speed standard 80% furnace, no air conditioners or heat pumps (that I know of) would match up to qualify for the tax credit. However, you could certainly remove the gas furnace and use a heat pump to heat and cool. Are your winters mild? Heat pumps are efficient down to even below 32*, so it may be worthwhile especially since your current furnace is only 80% efficient. Are your electric rates reasonable? If so, a heat pump would be a smart move in my opinion. So a heat pump could potentially save you money in the winter if gas costs are high.

I'm not familiar with how whole house fans work to answer your question re: temp control in the summer.

Thanks, Ryan. I'd love to know how you determine if an AC unit will match up or not. I'd been trying to figure that out on my own but was stumped.

Winters here are mild--lows hover around 32°F Dec-Feb and only rarely dip below 20°F.

I've seen some people recommend keeping a gas furnace and using it when it's too cold for the heat pump to work. Are there any guidlines for that?

Our electric rate is 7.4 cents per kilowatt (plus a $10 service fee) which seems to be pretty low based on what I've seen.

Thanks, again, for your comments. There are so many options it helps to read someone else's thoughts.

Here is a link that might be useful: Electric Rates by State

With reasonable electric rates (which I assume would be cheaper to operate a heat pump with than an 80% gas furnace with your gas rates), and a mild winter climate, a heat pump would be a good option in my opinion. You can keep the gas furnace for backup, though it may not see much use, and doing so would not allow you to leverage the tax credit since you'd need a variable-speed fan which boosts the efficiency for higher SEER equipment. What you would potentially install is a heat pump and a fan coil inside, and that would take care of the heating and cooling and could keep you the tax credit if you choose the correct components. A contractor should come to your home and discuss all this with you and hopefully do a heat loss/heat gain calculation to determine the correct size equipment.

I'll attach the link below where you can see what is a rated match (just a tip: keep the model numbers as simple as possible; for example, a Trane may be proposed as 4TWX5036A1000A, but in the database it only reads 4TWX5036A1 -- if you are having trouble finding results). The first link is for air conditioners, and the second for heat pumps. Your 58STA is probably not in the database because it isn't variable speed. Just so you see how it works, look at heat pumps and type in 4TWX5036 for outside and 4TEE3F for inside, and you'll see possible indoor fan coil matchups and their ratings.

Here is a link that might be useful: AHRI Directory

nolan

if comfort is what you are looking for, then a whole house fan would leave you disappointed.

I like the strategy of a HP for your area's relatively mild climate. plus you have very reasonable electric rates.

as to your furnace, it is a low end builder grade mdl. what is its age? if you are satisfied with its performance, then leave it alone.

go ahead and add a heat pump with matching evap coil. I do not like mixing brands and suggest you stick with Carrier or sister company Bryant.

you will need to stay with 13 SEER models with the new refrigerant-Puron. I recommend a properly sized Performance 13 Puron mdl or the Comfort 13 Puron model. either will do a nice job for you. you might need a new thermostat-ask dealer about that.

IMO
Good LucK!