HVAC For 2nd Story Addition?

watersda

I am in the process of designing a 2nd floor addition for a 1500 sf ranch. The current forced hot air, gas furnace is in the basement. I plan on having it replaced with a new Trane with central air. Will I be able to have one unit to heat/cool the 1st and 2nd floor? Can I have the duct work extended up through the 2nd floor into the attic and branch off to the seperate rooms from there? Or, will I have to have 2 seperate HVAC units, 1 for each floor? I am estimating $10-15K, am I in the ballpark?
Any comments/suggestions would be appreciated.

thom

It would make a better job to put a separate system on the second floor but certainly one system could handle it. 1500 sq ft on the first floor isn't all that much.

To add the second floor you will need a bigger system than was there to begin with. Bigger furnace, bigger a/c, and bigger plenums. You can't just extend off an existing duct and hope for it to work. It won't. The ducting needs to be properly sized and that means, Hire a PRO.

As for price, That depends on the ducting modifications needed.

coolmen

Now a days my builders have a 2nd sytem up stairs attic. most effiant and will not have cooling/balance problem with just one basement system.

mdshunk

I'd do one on each floor, such as is customary. If you insist on one unit for whatever reason, zone dampers for each floor and an ECM motor in the air handler are what I'd reccommend.

A.D. Const

I Agree!!!
With two different units you will have a much better flow control hence better cooling/heating, plus you'll only be working for the second floor duct, saving you time and work trying to resize your original duct if you went with only one unit. Plus it represents your work more professionally. At least that's my opinion.

If on the other hand, if you go with a whole new unit and duct for both floors, the way to maintain some flow control would be the zone dampers and ECM... If you do follow this route don't forget to properly allow for return air for the second floor as well. In short as THOM said "The ducting needs to be properly sized and that means, Hire a PRO."

watersda

Update:
I had 3 local trane dealers come to give me qoutes. 2 of them did, 1 came and looked at the job, but ended up blowing me off for the quote. The 2 that did were very close to each other. 1 qouted XR12 Central Air units with the old refrigerent. I asked him to reqoute with the same model #'s I got from the other dealer and they were within $800 of each other.
The concensus was 2 seperate units.
1st floor: Replace downstairs furnace with high efficiency trane (95%) and a 2.5 ton trane XR14 central air unit, extend a few ducts. ~$8000
2nd floor addition: 80% eff. trane furnace in attic, all new ductwork, 2 ton XR14 central air unit. ~$12,000

~$20,000 total, installed. Seems reasonable?

747

Wow running ducts must be expensive. Thats sticker shock in my oppion. But i really don't know. I know more about hotwater then forced air. But my plumber likes armstrong forced air furnances with AC.

gregj

Is your second floor addition not the full 1500 ft? Otherwise I'm mystified as to why a smaller A/C is needed for the second floor since most of the summer heat will be coming through the attic. Why not use a high efficiency furnace for the second floor? It wouldn't add much to the cost relative to the whole job.

watersda

I am assuming the cost metal has a lot to do with the high price. New ducts 2nd floor, copper line for the 2 AC units and gas line to attic for 2nd funace. In my area of the country, we can't have condensing furnaces in the attic, could freeze. I'll ask the dealer as 2 why the different size of the AC unit.