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Old 10-13-2008, 10:55 PM   #1
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Looking for feedback on zoning forced air system


I have an 1800sf ranch and recently finished the basement which is about 1100sf. I would like to split the main level and basement into separate zones. Attached is a design proposal of the zones. Am I on the right track here? Anyone see any issues or have and suggestions? Thanks
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Old 10-13-2008, 11:25 PM   #2
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Looking for feedback on zoning forced air system


Looks good to me.

Why do you want to zone your system?

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Old 10-14-2008, 08:11 AM   #3
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Looking for feedback on zoning forced air system


Basements don't require as much heating or cooling air flow as the first floor does.
How did you determine your duct size.
Are you adding returns.

Your connection from the existing 8 x 18 to the new 8 x 18 is extremely restrictive.
The new 8 x 18 should be vaned off cnter to direct air flow for the sections CFM as required.
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Old 10-14-2008, 09:59 AM   #4
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Looking for feedback on zoning forced air system


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Originally Posted by beenthere View Post
Basements don't require as much heating or cooling air flow as the first floor does.
That can be controlled by duct size and vents.
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Old 10-14-2008, 10:36 AM   #5
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Looking for feedback on zoning forced air system


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That can be controlled by duct size and vents.
True.

But. His drawing shows no bypass, or other provisions for protecting the furnace from riding its high limit, or the A/C from freezing.

We can guess that he is going ot use a zone system with discharge air sensors.

But, he does not say.

Guessing the original installer just sized the ducts by .1"FR, good chance its a 3 ton A/C system. Maybe 3.5 ton.

The basement may take .75 to 1.5 ton for cooling, depending if full walk out, or totally below grade. He now has a lot of excess air/capacity to deal with.

Often times, its better to slave a low load basement, instead of having it as a controlling zone.
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Old 10-14-2008, 10:51 AM   #6
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Looking for feedback on zoning forced air system


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or the A/C from freezing.
That is one of the reasons I like hydronic cooling. No chance of freezing the coil.
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Old 10-14-2008, 11:04 AM   #7
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Looking for feedback on zoning forced air system


Average home owner, won't like the cost of it though.


They don't realize the savings a mini chiller can have when you zone.
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Old 10-14-2008, 08:07 PM   #8
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Looking for feedback on zoning forced air system


I want to zone my basement so that I can control the temp with a tstat.

The basement is totally below grade but there is one large egress window.

I do plan on adding 4 or 5 returns and 10-11 forced air ducts.

I have a Lennox 10ACC-030-230-03 compressor. I believe it's a 2.5 ton system.

I was concerned about air flow restrictions which is why I asked for feedback. I did not consider using a bypass or air discharge sensors. I see where I would want to use the bypass.

I offset the new 8x16 duct because a conduit and galvenized gas line possibly prevent me from placing it in the center, I may however might be able to squeeze it in there. The lines to the compressor outside may be more of an issue.

If I move the new duct to the center and add the bypass, does my design look okay? Code requires me to have a system exchange air once an hour in the basement. Would I be better off just adding one or two returns with 4-5 forced air ducts off the main system? Would this impact the effeciency of the main level?

Thanks for your comments!
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Old 10-15-2008, 06:21 AM   #9
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Looking for feedback on zoning forced air system


You should do a calc to know how much air the basement really needs.
That way you don't short cycle. And can maintain temp.

The returns should be able to remove as much air as the supplies can put into the basement.
Its not the number of either that counts, as much as the total air they can move.

If you install a large number of supplies. But have vey little air flow in them. The air doesn't mix well. And you end up with a cold basement.

4-8" supplies can work better then 11-6" supplies for that reason.
The type of register you use, also makes a big difference.
For a basement with supplies in the ceiling, a register that throws the air down is better for heating concerns.

The positioning of the supply trunk for the basement isn't as important, as how its connected to the system.

The connection the drawing shows about a 250' equivalent length(more for air flow back in the direction of the 10 x 8), counting the originating 18 x 8's tap into the supply plenum. So its an air flow issue already.

Tapping into the side of the plenum, running a trunk out past the lines, and then a ell up into the new basement duct can work better. But requires vanes in both the ell, and the 18 x 8 duct. It also takes up head room in that area.

Your basement may only require 400 CFM for heat.

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