New A/C Question

Old 05-28-02, 10:15 AM
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New A/C Question

Hi All:

I am in the process of having a new home built in NE Fla. The house is a 2 story and there will be a split TRANE system; (3.5 tons down and 2.0 tons up ) for a total of about 3K sq feet cooled/heated.

1) Is there any benefit to the new R410a refrigerant as opposed to the R-22? I was quoted 5K to go from the R22 Trane 14XL SEER system to the R410a. Based on my own research, it doesn't sound like I would be seeing any ROI with the R410a; it's more expensive (for now) and availability is not yet widespread.
What are your thoughts?

2) This is of much more concern to me than the first question. My house was designed in such a fashion that there appears to be little room between the floor joists between the first and second floor. So little room in fact, that the a/c subcontractor was saying it would be nearly impossible to get a 20" return flexible conduit to the other side of the first floor. There is about 1900 sq foot of cooled space on the first floor; part of the problem is that about 1/2 of the lower level has attic accessible space to run the a/c venting and returns, the other 1/2 of the first floor is under the second floor. If the a/c subcontractor places returns only on one side of the house, will this provide adequate return? in situations where space is limited how can you get adequate return to an air handler in the garage? Instead of a 20" conduit, could you not do 2 10" conduits and then join them to a 20" in the attic? My concern is that some skimping might be done and I really do not know what will happen if there is only a return say in the hallway on the side of the house closest to the air handler and none in the living room and family room (the far side of the house) opposite the air handler.
I do know that a Manual J calculation was done; would that not specify the proper amount of returns for the home?

3) The second floor is serviced by the Trane air handler that is in the centralized closet on the 2nd floor and I presume that the air handler will pull air in through the closet door and would not require a separate return?

I am posing these questions to my a/c contractor, but it always helps to have a second objective opinion. I am not an a/c contractor myself obviously; but I feel I know more than your average homeowner.

I welcome all constructive advice and comments.


Old 06-08-02, 01:32 AM
lynn comstock
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1) An extra 5k for the upgrade? No way. and Not Yet. R-22 will be around for quite a while and the new refrigerant and technology is still TOO new for me.

2a) Don't concern yourself about needing more than one return unless you plan to close doors in the various rooms. The air needs a way back to the unit. Grilles in the doors or open doors work fine.
2b) A 20 inch duct would have to be replaced by at least FOUR 10 inch ducts (to match the cross-sectional AREA).
2c) Don't buy from any dealer who fails to do a Manual J Heat Load in writing.

3) If you want a VERY QUIET system you want at least 6 to 8 feet of return duct with at least one or two turns. This is a sound trap between you and the indoor fan. The closet can be slightly bigger to allow the return to go up the the high sidewall or the ceiling nearby.
If your home were here in Yuma, AZ, I doubt that you would need more than 3.5-ton to 4-ton for the entire home. We have serious HEAT here. The home could be cooled with a single unit if the ductwork is designed well and zone control is used to send the cooled or heated air according to the needs of the zones. Dampers are controlled by thermostats to do this. The cost to buy, repair and maintain 1 system is much less than for 2. For Zoning see:

See the following article about unit sizing.
Old 06-08-02, 07:29 AM
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Thank you very much for your reply. The sub-contractor did in fact do a Manual-J calculation for the house. As it turns out, they increased the air handler size on the 2nd floor by 1/2 ton to compensate for an error that forced the builder to raise the 2nd level ceiling by 1 foot across the entire floor. So, now it sounds like I have almost 6 tons of air movement, 3.5 down and 2.5 up. Sounds like a lot of power for 3000 sq ft, but I am a network engineer not an a/c contractor. I have a friend of mine that is an a/c contractor; I am seriously considering having him come in and zone the system (presuming it can be done). I did read the article you sent me Is zoning (after the fact) a possibility once the house is complete? I would rather him do it now, but that is not an option in this case, since it isn't tehcnically my house until I sign on the dotted line. I do believe that all of the main trunks will be accessible albeit more difficult to get to. This current contractor doing the a/c doesn't seem to think these sorts of options are needed. If I had the choice of another sub-contractor (which I don't), I would have done things differently.
Again, thank you for all of your advice, I found it quite useful.

Old 06-08-02, 08:22 PM
lynn comstock
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Sounds like you are locked in.

You WILL have 2 zones (2 machines) and more tonnage than you need (especially downstairs). Contractors tend to make the manual J load come out to what they BELIEVE because they need to feel safe and do not want any job to embarrass them.

Keep them maintained well, and clean and you will have good results.

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