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Old 03-28-2010, 08:41 AM   #1
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new construction- HVAC design help


I am in the process of having plans drawn for our new home. This will be the second house I've built as GC. It will be a one and a half story, 1500 s.f with two beds and bath upstairs, located in northeast GA.
First off....THANK YOU for your help.......also I wanted to ask these questions before I talked to HVAC subs, so I know what I want when asking for their bid, and make sure we are on the same page.
A little background---What I have in my current 1300 s.f ranch (crawl space) has a package unit outside (electric) with one big return duct that runs up through an inside wall to attic (in about a 2'x2' chase inside a bump out in a closet wall) and the return vent is located in the ceiling in the center of house. We did this so we wouldn't have a big return vent on our living or dining room wall. The supply vents are located in floor under windows when possible.
New home, (1500 s.f. 1-1/2 story, 8' ceilings, no vaults) I was planning on having one package unit, electric, or if it was a split system, handler under house, NOT in attic. Any opinions on split versus package? Next question is would you recommend two zones? (I can live with a few degrees difference)
Next question is more about duct work.
On the new plan, my uncle who is an engineer and has been building houses for many years, is suggesting---locating the unit under the crawl space (I might of misunderstood and need to ask if he meant the whole unit or a split system w/ handler only underneath) and have several smaller returns that fit inside 2"x4" walls on first floor (with vents on wall insted of floor), with supply vents on outside walls and return vents on inside walls and upstairs have vents in ceiling. With one enclosed wall chase about 2'x2' running up the first floor wall to attic for return and supply ducts for upstairs.
My wife and I do not like the idea of having vents in wall instead of floor, unless it was one big vent in a hallway wall as opposed to several smaller ones in various rooms. I guess we could make the supply vents in the floors easy enough, but what about the returns? Can we do one big one in ceiling on new plan,( first and second floor if needed)
Sorry to be so long winded but I wanted to explain as best I could as this is obviously important to design. I might have follow-up questions as well.
P.S. If you know of a good HVAC company on the Athens Ga area let me know


Last edited by ugabulldog; 03-28-2010 at 08:48 AM.
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Old 03-28-2010, 11:18 AM   #2
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new construction- HVAC design help


For balance and comfort the best way to go is with properly sized returns in every room where a supply is located. I would probably go with a split system, air handler in the crawlspace for cost and convenience reasons. Unless the spaces are separated by close able doors, there is little advantage to splitting the zones and a whole lot more expense.

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Old 03-28-2010, 11:21 AM   #3
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He may have meant supplies on outside walls to mean at the walls. Not in them.

The returns he means in the walls. If your first floor plan is an open plan. Then you only need on central return for the first floor.

Second floor. You probably want a return in each bedroom, plus on in the upstairs hallway/landing.

Split or package doesn't really matter.
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Old 03-28-2010, 04:48 PM   #4
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Quote:
Originally Posted by beenthere View Post
He may have meant supplies on outside walls to mean at the walls. Not in them.

The returns he means in the walls. If your first floor plan is an open plan. Then you only need on central return for the first floor.

Second floor. You probably want a return in each bedroom, plus on in the upstairs hallway/landing.

Split or package doesn't really matter.
He meant supply in walls,... but it should be just as easy to put in floor I'm assuming. If I have one return on first floor, I need to allocate space for it since it won't fit inside 2"x4" walls like several returns would, right? Also it would need to be in a central location in an open floorplan. The space I had allocated now for supply/return pipes to second floor is on an outside wall in a closet both upstairs and downstairs, so I would need to allocate two spaces instead of one, right?
And then if I had one big return for downstairs, and i wanted it in ceiling instead of wall, it couldn't fit between floor joists or go thru them if I used a wood I beam because return return duct would be too big,...correct?

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Old 03-28-2010, 05:35 PM   #5
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With the duct work in the crawlspace. A large chaise is needed for the upstairs return.

No, a single return for the first floor won't work well trying to use only one or 2 of the 2X4 cavities.

Never heard of an HVAC engineer that wanted to put supplies in the outside wall blowing inward.

Sounds like you REALLY need one or 2 local HVAC contractors to go over your plans one on one with you.
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Old 03-28-2010, 06:04 PM   #6
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Quote:
Originally Posted by beenthere View Post
With the duct work in the crawlspace. A large chaise is needed for the upstairs return.

No, a single return for the first floor won't work well trying to use only one or 2 of the 2X4 cavities.

Never heard of an HVAC engineer that wanted to put supplies in the outside wall blowing inward.

Sounds like you REALLY need one or 2 local HVAC contractors to go over your plans one on one with you.
Thanks for your help....just to be clear, he was saying the supply vents would be located inside the walls, however he mentioned using the exterior walls.
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Old 03-28-2010, 06:07 PM   #7
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You need an HVAC guy to do your HVAC design. Or you'll be cursing your uncle.
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Old 03-29-2010, 07:13 AM   #8
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Here is my input as a homeowner and frustrated heat pump owner.

I didn't see it mentioned but I suspect this will be a heat pump?

If I were building a house, I would never again have the HVAC in the crawl space or attic. I have a HP with the air handler installed in the crawl space and after nine years had to install a new air handler due to corrosion.

Also, from what I know, the air handler is not insulated to the same level as ducting. Again, if in the crawl space or attic, a lot of heat will be lost. Cooling efficiency is also an issue if in the attic.

So, the HP air handler should/must be installed in the conditioned space of the house, never in the crawl space or attic.

Next ducting. I would never again have ducting in the crawl space, attic, or walls. Plan to have the ducting in the conditioned space. It can be done if you plan for it. A little bit of extra work in the design of the house, but the payoff will be there in a more efficient heating and cooling system.

I applaud you for wanting to do your homework before contacting HVAC companies. Maybe its just in my area but I'm not impressed with the level of knowledge or installation skills that I have dealt with.

I used this program to do a heat loss heat gain calculation on my house. Was worth the few dollars I paid for it. http://www.hvaccomputer.com/

This also helped.
http://efficientcomfort.net/jsp/ResDuct_Web.jsp
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Old 03-29-2010, 03:23 PM   #9
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Air handlers in crawlspaces only rust out if they are not maintained. Or the crawlspace is damp. Which it shouldn't be, if its done right.

Air handlers for unconditioned spaces are suppose to be ordered with the proper insulation in them. So that was an installer created problem.
Conditioned space is always the best place for duct work.
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Old 03-29-2010, 03:51 PM   #10
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BT,

I don't doubt what you're saying is true. As I stated, this is my opinion as a home owner, not a HVAC installer. Quite possible I live in a technically challenged area.

I will check on the AH insulation you mentioned. It's one thing to have the wrong AH installed the first time, but no excuse for installing the wrong one twice. But I doubt there is anything that can be done about it now.
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Old 03-29-2010, 04:09 PM   #11
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You may or may not be surprised how many people/installers don't know that air handlers come in more then one insulation rating.

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