2 units vs. 1

[tchomes]

I am currently collecting bids for a new house I am building. I have requested High Efficiency equipment from all trades with Manual J Calculations. Currently comparing the Trane, Carrier Infinity and Lennox variable speed systems. A couple of trades have submitted a design for 1 4-ton unit and the others have suggested a 3-ton and a 2-ton A/C unit. Will be using ~90+% efficeincy propane furnace and whole house filtration system.

The house is 2600 sqft downstairs with an optional 800 sqft bonus room. The width of the house is 80ft. Looking for multi-zone and multiple return vents.

Big question, is it better to have one unit vs. two, or not?

[comfortdoc]

I would look for 2 units. Depending on the layout of the house and how the units are split that might be the only zoning you need to do.

[rickboggs]

It would be easier control temperatures between upstairs and down if you used two units. Remember heat rises, cool air falls. One tstat, two natural zones... pain.

[beshvac]

2 units....you have somewhere to sleep when one's broke and you don't have to go to walmart and buy a window shaker. (My wife will NEVER be without AC.

[wolf225]

I'd recommend 2 units. If the house is a 2 story, I'd put a 90% furnace onn the 1st floor and an 80% horizontal in the attic for the 2nd floor. Since the attic is an unconditioned space I don't have problems with the condensate freezing and low ambient air temps messing with the air proving switch in the winter months. Two systems also means the customer is not likely to loose heat in the entire house on the same day. If the house is designed tightly sealed then I also recomend hot air exhaust recovery ventilators,

[yocona]

Originally posted by beshvac
2 units....you have somewhere to sleep when one's broke and you don't have to go to walmart and buy a window shaker.
You can't argue with that logic.

[tchomes]

Will two units cost more to operate than 1 unit? I agree with two units when cooling the extra bonus room, but do you think one unit and multi-zoning would be efficient for the lower rooms? 80ft from one end to the other bothers me a little. I am not for sure if I can get cold air from one side to the other evenly.

I like the idea of 90+% for downstairs and 80% for the bonus room.

[tchomes]

Do you recommend staying with one system for everything? If I choose Lennox, Trane or Carrier, should all equipment and filtration systems be from that manufacturer? Should I be determining the best system or individual components?