Hi - because of my experiences with my own system (search my username if you want to hear the tales 8-}), I got asked to help my brother with his remodel.
They're in NY, I'm in New England, and they are paying contractors for the whole job. I'm posting because I want to make sure they are getting exposed to all their options. Anyway, the house is in the suburbs of NYC. It's a ranch built around 1950, with about 1800 sq ft on the main floor and a full basement. It has Forced Hot Air (gas furnace). It currently has an older (oversized) 100K+ BTU furnace with integrated (also somewhat oversized, though I don't have the exact #) A/C. My dad lives at the far end of the house (opposite end of the other bedrooms) in a separate 12'x 12' bedroom with its own full bath.
They're adding a 2nd floor of about 1300 sq ft to the house, and doubling the sq footage of my dad's bedroom, and doing some re-dividing of the bedroom living space on the main floor. One annoyance for construction is a cement slab between the main floor and the basement. (there used to be one between first floor and attic as well, go figure).
ANYWAY - The HVAC guy is recommending adding a 2nd system in the attic, properly sized for the 2nd floor (Carrier Infinity, 92+%, VSP) to cover the 2nd floor, and other than some opportunistic ductwork adjustments, leaving the existing system about the same. He's amenable to replacing the basement system. We're thinking of letting him replace the basement system (again, with a Carrier Infinity) so that we can zone my dad's room separately. Still, I have some questions for you experts...
1) I had suggested that perhaps the "right" solution was a new single system in the basement to cover the entire house. He says that is not the best choice, and that it's not even a comfort win because to cover the 2nd floor he'd have to run a plenum up to the attic and feed the 2nd floor down from there anyway. I was thinking the existing duct work could be expanded and added to (with much routed in the floor of the 2nd floor) to equip the house as if it were being built from scratch. Is he correct that if this was new construction, 2 systems would be the right approach?
2) Should I be worried at all about heat comfort on the 2nd floor since the heat is being pushed down? Contractor says that 2nd floor is somewhat warmed by heat rising from first floor, and that although most registers are positioned on the ceiling over windows, a few will be put lower down. He also said that whatever he does to position the registers for heat is fine for A/C because "for A/C it doesn't matter where the registers are".
3a) With all that ductwork (and possibly a system) in the attic, should we put an exhaust fan at one end of the attic?
3b) As you may note, the 2nd floor is smaller than the first, and so at either end of the house, there is a first floor room with a big unconditioned "crawl" attic space over it. In both situations these are bedrooms. Will a buildup of heat (or cold in the winter) in these crawl spaces cause issues for the room below it, or adjacent to it?
4) How important do you think it is to replace the basement system now? Should there be a significant cost advantage to having him replace the basement system now while he's doing other work?
5) If we don't replace the basement system, it was suggested that we could put a slightly larger system in the attic, and tap the new system to create a separate "zone" for my dad's bedroom. However, the bedroom will be 2 stories below the system (system in attic, bedroom on -first- floor). The space under the bedroom is unheated storage space, and so I 'm concerned about relying on pushing heat -down- 15-20' as the -primary- heat for the room. am I off-base here?
6) Anything else I should be asking or concerned about?
thanks guys, - you're the best