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Discussion Starter · #1 ·
Have 12" metal round duct that I want to use for return Air in my basement. I have 3 ton system. I bought a return grill of size 14"X14". Is this enough ?
My basement is roughly 1000 sq ft.
Note: Have installed four 5" flex duct ( register 10" X 4") in my basement.
Thanks
 

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14 x 14 is fine. Per Hart and Cooley, data will allow 465cfm @ 500fpm. You are well below that with 4 - 5" supplies. If you use the 12" round you should install a damper. 10" round would be better, but it's not critical. You don't want your basement to be under negative pressure.
 

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Have 12" metal round duct that I want to use for return Air in my basement. I have 3 ton system. I bought a return grill of size 14"X14". Is this enough ?
My basement is roughly 1000 sq ft.
Note: Have installed four 5" flex duct ( register 10" X 4") in my basement.
Thanks
Both the supply and the return are sized for the ventilation needs. Why are you doing this?
 

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The best way to do this is to find the information from the manufacture.
My opinion is 12" is woefully to small along with a 14x14 grill.
I had a 3 ton ac a home and it had a 20 x 14 return grill and and an 18" duct. Which was to small.

If you are adding another return to your system please contact a pro where you live. Adding a return is not like changing an light bulb. There is more to it than what meets the untrained eye.
 

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I am finishing my basement. so I need heating and cooling in the finish basement.

thanks!
You'll only have about 200 cfm with the four 5" ducts. It'll probably me be enough to keep it comfortable but it'll be a tad stale. A 10" duct would have been more than enough. Like it's been said, make sure you can damper it down.
 

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Discussion Starter · #7 ·
The best way to do this is to find the information from the manufacture.
My opinion is 12" is woefully to small along with a 14x14 grill.
I had a 3 ton ac a home and it had a 20 x 14 return grill and and an 18" duct. Which was to small.

If you are adding another return to your system please contact a pro where you live. Adding a return is not like changing an light bulb. There is more to it than what meets the untrained eye.
this is in my basement, h
14 x 14 is fine. Per Hart and Cooley, data will allow 465cfm @ 500fpm. You are well below that with 4 - 5" supplies. If you use the 12" round you should install a damper. 10" round would be better, but it's not critical. You don't want your basement to be under negative pressure.
I can return metal duct of 12" and buy 10" instead. One more thing, since I have installed manual damper in my all supply to keep them close in summer, Do i need close/block the return air as well ?

what is best Damper or Magnetic vent cover ?

thanks!
 

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As you can see from the chart below a 14x14 grille will be more than enough to stay below 500 FPM. You probably want to size your return duct for 300 CFM, so 10" round duct is perfect and I would install a damper too. You can buy a start collar or spin in with a damper to attach to your return duct. They might just sell the round damper too. If you are closing the basement vents in the summer the return damper is recommended.

Damper: SPEEDI-COLLAR 10 in. Take Off Start Collar with Damper for HVAC Duct Work Connections-SC-10D - The Home Depot


Rectangle Font Pattern Parallel Number
 

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Discussion Starter · #10 ·
That start collar I linked had 1 (bad) review. Here's another with 1 (good) review.

Thanks. I found this even better from Grainger and its 26 gauge,

GREENSEAM Galvanized Steel Collar W/Damper, 10 in Duct Fitting Diameter, 5 in Duct Fitting Length - 6EKH6|GR6POCR10GA26D - Grainger
 

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We don't know what your supply air cfm is and what your return cfm will be. Duct and grille size based on what's possible. I'd light a big stogie and stand at the top of the stairs watching the smoke while someone adjusts the damper when the furnace is running. Adjust the damper until the basement has a very slight negative to neutral pressure. The basement door should be cracked open 2" or so while you adjust. Mark your setting on the damper so you can set it every fall after the cooling season. Not hi-tech but It actually works quite well.
 

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In case you don't smoke, or use incense, a tissue paper will work too.

If the basement door is undercut, you can use a tissue paper and see it fall neutral when placed in the gap. (if the door isn't undercut, then prop it open with something to get a 1-2" gap.)

Adjust it for summer and winter like @57TinkerMan mentioned.
 

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Sealing the seems will help. But you may have outside air getting in that joist space. Or, one of the pipes in the joist space is allowing higher humidity air to get into that space.
 

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Discussion Starter · #19 · (Edited)
We don't know what your supply air cfm is and what your return cfm will be. Duct and grille size based on what's possible. I'd light a big stogie and stand at the top of the stairs watching the smoke while someone adjusts the damper when the furnace is running. Adjust the damper until the basement has a very slight negative to neutral pressure. The basement door should be cracked open 2" or so while you adjust. Mark your setting on the damper so you can set it every fall after the cooling season. Not hi-tech but It actually works quite well.
I am back with one question,. there is no door between basement and main living area. I am still good with 10" duct return and 14X14" return grill right ? thanks!
 
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