question on heating/cooling the second floor

[mcelhane]

I am in the planning stage of building a new two-story home that has

2000 sq.ft on the first floor and 1000 sq. ft on the bottom. The conventional wisdom here is to have two HVAC units, one for each floor. I can live with that. However, I have been advised that the second story unit is usually a split unit with the unit in the attic space of the second story. I don't like this idea for several reasons: First, I'm going to be installing a gas furnance, so the thought of a furnance in the second story attic just scares me (carbon monoxide and fire danger). Second, I hate split systems - more joints for freon to leak from. Third, repairability seems problematic with a system partially in the attic space. So, I was thinking that I could put the second floor unit on the ground floor (complete package - not split) and duct the air up the side of the house. I could build an insulated "chase" around the ductwork so that it looks nice. However, is sending the air up two stories (to the attic of the second floor) reasonable? Can the fan blow hard enough to make the right angle bend that I'm putting in the ductwork and can I get enough air flow? Is this a good or bad (or stupid) idea? Comments welcome

Thanks......russ mc.

[Bob]

According to Hank Ratkowski, from ACCA, there's no drop in CFM until the first take off "no matter how long the trunk duct is". If you're using a 90+ gas furnace, you can't put it in most attics. Personally, I'd put an 80+ in the attic. If you have to worry about joints leaking in split system refrigerant tubing, then you need to start looking for another contractor.

[Goedjn]

I think you should install Burham's Duo-Rad hydronic air convectors, with piping to both a boiler and a water-chiller, and then post back in a couple years and let us know if they actually work.

--Goedjn

[SQLit]

What you suggest is not a bad idea, it is a REALLY BAD idea.

Splits are done every day where I live. Silver solder is used for the freon joints and very few compentant HVAC mechinics have trouble with the joints. Besides they pull a vaccum on the lines before charging them. Any leaks are apparent when trying to pull a vaccum.

Do you want to look at a 36 inch box on the side of your house per unit?

Please call some licensed contractors in you area and pose these questions to them. After they provide you with the manual calculations for load and air flow. And quit laughing.

[barry]

Duct size for 1000 ft^2 should be manageable in a central partition on first floor, with dampers in ductwork to zone heating/ac from single unit in basement.

"hate" split-units? Certainly no more a problem than system with freon evaporator in central unit. IMHO, only real negative would be having yet one more outdoor unit, though that might turn to your advantage. CO and fire hazard with furnace in attic? Tell that to UL.

Generally, only significant problems with air-movers in attic, that I've seen, are sometimes difficult access for service, and noise transmitted through ceiling.

Gonna talk to local contractor soon?

HTH, J