Or, you could T it in and see what happens. It might be just fine, what have you got to lose? A few hours of work and a few bucks' worth of sheetmetal. I'm sure a professional could come up with a multi-thousand dollar solution. In fact, call a couple of them out and see what they say. Should be interesting. "Never ask a barber if you need a haircut..."

As a general rule, general contractors know very little when it comes to HVAC. They like to hire the lowest cost HVAC contractor in the area since the budget for HVAC is a low priority when building a house. You are doing the right thing by questioning what the HVAC contractor is "suggesting". New houses have no heating and cooling history so in my opinion a heating and cooling load calculation must be done. There is no excuse for guessing the required sized. This often leads to an over sized system which will never operate correctly or efficiently. The online calculators are OK for a ballpark estimate, but it is not a substitute for a load calculation. Based on the information you have given so far, I think for new construction a 80K BTU furnace and a 4 ton AC would be the right sizes assuming the equipment will be installed in the basement and all duct work is in conditioned space. This could change if you have a lot of glass. At 3400 sq. feet I would suggest either zoning the first or second floors, or having a furnace and AC for each floor. The two systems are initially more expensive, but you will save money on operating costs if you use temperature set backs. It is the best way to get even temperature distribution in the house. I question the wisdom of a whole house fan in a house the has an Infinity AC. If you live in a humid area, then you will allow humid air to enter the house every time you use the fan. In my opinion you are better off setting the thermostat at 78-79 and keeping the humidity at 40%.

Hi, I'm in the midwest and have a 5100 sq ft home. I'm looking at replacing my 17 yo furnaces, 2 Carrier Weathermaker high efficiency , with electronic filtering system , (eletroair SST), two air conditioning units, one blown and one 4 years old (got 10 years out of the blown one) with a similar set up to above. Recommended by the dealer is 1 American standard 16, 2ton communicating heat pump with a Am ST. Freedom 95 60K btu, 3 stage furnace and Acculink 900 comfort controller... AND 1 Heritage 16, 3 ton communicating heat pump with Freedom 95, 80K btu, 3 stage furnace, both with the AccuClear air cleaner system. We could keep the 4 yo air conditioner for a while, and put in the extra heat pump later. We could keep the current air cleaner (the kids, who sleep near it downstairs say it cracks and pops a bit). I'm looking at getting another quote, and from the looks of it above Carrier would be the place to get another quote and opinion. The American standard dealer made a big deal about the communication between the furnace and heat pump, calling this "geothermal above ground, at 1/3 of the price". We probably could get a couple more years out of our furnace, but has needed repair a couple of times, and were told it could become a problem, which we'd like to avoid in the middle of winter. We did consider geothermal and priced that out last year, and just felt the retrofit wasn't worth the bother. A contractor friend recommended that future high efficiency furnaces would make the geothermal unnecessary, at least for retrofitting. Any opinions out there?

An unconditioned attic is the worst place to install HVAC equipment and duct work. I would avoid it if possible. If you are in DC or one of the bordering states then 14 SEER is the minimum allowed. For a walkout basement having a separate zone is a nice feature for heating, you probably don't need it for cooling. The $5K price is steep for a thermostat and some dampers. Do you know the model numbers of the HVAC equipment. At the very least you should have 2-stage equipment if you are going to add zoning. Find out if the $5K covers upgrading the equipment for the first floor.