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Old 06-04-2009, 08:43 AM   #1
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Where to put Return air vents in basement


Greetings:
I am finishing the basement. I drywalled before putting the return vents. I have pictures and can locate where the return ducts are and will be able to cut and put the vents. In case of rooms where the return ducts may not be running through, how do I put the return vents and be code compliant. Attached is the layout with approximate size of the rooms.

Thanks!
Shaw
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Old 06-04-2009, 10:19 AM   #2
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Where to put Return air vents in basement


You obviously need to run return ducts to where the return vents will be. Is that the question?

The supply and return layout should have been designed by an HVAC guy for best performance and comfort. Location of return vents is often a choice of how good of a system do you want to pay for. Some might go with one return in the big room and that might work fine if the other room doors are usually open or have a big enough gap between the door bottom and the floor. Others would want returns in the other rooms (except bathroom and furnace room) for optimum comfort. Lincoln Town Car or Ford Fiesta - your choice.

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Old 06-04-2009, 03:44 PM   #3
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Where to put Return air vents in basement


Run a central return, and under cut the doors.
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Old 06-04-2009, 04:42 PM   #4
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Where to put Return air vents in basement


Woah, brain fart. I just typed a reply and missed the crux of this. I think the other guys did too..

To recap:

You already have the return ducts running throughout the basement. You just need to cut through the drywall to access the termination of each duct in order to attach the vents covers.

So the question is whether you need to run additional return ducting to those rooms in the basement that don't already have returns. Right?

I don't think code specifies that you need a return duct in each room (maybe in your area, but I've never heard of it).

If you have enough return ducting now (by cross sectional area) to support your blower, then you should just under cut the doors to the rooms w/o returns, as beenthere said. Things might be a little lopsided, but hey..

Quote:
Originally Posted by jogr
The supply and return layout should have been designed by an HVAC guy for best performance and comfort.
jogr is right, but it's a DIY forum, and I don't think you need a pro if you do sufficient planning; but did you do any calculations to size your ducts, or did you just wing it?

Last edited by ScottR; 06-04-2009 at 04:46 PM. Reason: Grammar.
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Old 06-04-2009, 04:48 PM   #5
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Where to put Return air vents in basement


He may mean the return duct that was installed originally.
Which may never have been sized to be used for the basement.

Very common, because of pulling combustion vapors from the chimney.
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Old 06-04-2009, 05:06 PM   #6
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Where to put Return air vents in basement


Quote:
Originally Posted by beenthere View Post
He may mean the return duct that was installed originally.
Which may never have been sized to be used for the basement.

Very common, because of pulling combustion vapors from the chimney.
OIC.. You may be right. One thing is for certain; we need clarification.
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Old 06-04-2009, 07:33 PM   #7
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Where to put Return air vents in basement


Oops I made a typo.
The V1 thru V8 marked in the drawing are existing Vents. There are no Return Vents in the basement. I am trying to figure out where I should put the Return Vents.

<beenthere> suggested to run a central return and under cut the door.

What should be the size of the central return vent ?
How many inches off the floor can the bottom of the return vent be ?

Undercutting the door -> how many inches gap should I have? Instead of cutting the door, Is it Ok, if I do a vent in the wall ? What size the vent has to be ?

ScottR: The original builder had the HVAC roughed in the basement. I hope he had done the calculations - they were professionals.

Thank You
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Old 06-04-2009, 09:13 PM   #8
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Where to put Return air vents in basement


Your return in the basement, should be size to equal the amount of supply you have in the basement.

Door under cut shuld be 3/4" to 1" depending how much air is supplied to the room.

Return grilles cut through the wall would be sized to to equal the supply to that room.
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Old 06-05-2009, 07:54 AM   #9
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Where to put Return air vents in basement


Thank you All

To summarize,
(1) I have to add up the total area of all vent openings and make sure that the central return is at least that size.
8 vents x 31.64 sq inches = 253.12 sq inches. That means the return has to be around 16x16"

(2) From each room I have to make sure that if the door is 32", give 1" gap in the bottom. or do a return vent on the wall same size as the vent

I still don't have the answer on the height from the floor that I should mount the return ?

-Shaw
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Old 06-05-2009, 10:50 AM   #10
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Where to put Return air vents in basement


As far as height you don't want to make your baseboard installation difficult so be sure the bottom of the vent is above the top of the baseboard.

If you're putting through-the-wall grills in the other rooms I'm pretty sure they offset the openings so light and sound don't have a straight shot through. Put the grill high on one side of the wall and low on the other.
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Old 06-05-2009, 11:06 AM   #11
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Where to put Return air vents in basement


sjahan22,

Sorry for the misunderstanding. IMO, under the stairs on the side opposite the furnace room would be a great place for the return; very easy to run. That's assuming there's nothing in the way, of course..

I don't think you need to add up the sq. in. of each of the vents, just match the size of the return to the size of the supply trunk (in theory you could have a lot more cross sectional area on the vents than on the trunk). <-- I'm sure beenthere will correct me if I'm wrong, which I may very well be.
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Old 06-05-2009, 11:36 AM   #12
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Where to put Return air vents in basement


Put your return grille about 6" above the floor. That allows room for your trim work.

Size of supply duct has little bearing on size of return duct, or return grilles.

Transfer grilles need to be larger then the supply registers, since your moving the air through 2 grilles.
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Old 06-08-2009, 09:35 AM   #13
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Where to put Return air vents in basement


Thank You All. Appreciate the help

-Shaw

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