Adding Return Air Ductwork 12"X12" DIY

Out of curiosity. I understand sucking up more of the warm air is beneficial.. but would it cause problems to have too much air being sucked into the hvac?

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AC topics seem to be the norm these days and interested if anyone has added a Return Air to their system, DIY, and the steps involved? Looking to ADD a 12"X12" in our bedroom to help with the movement of air on these hot summer days and AC company's time is at a premium, currently.

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I did this a few years ago. I bought a flat piece of sheet metal from Lowes along with duct, return grill, and a fitting to tie the duct into the plenum.

Overall, its not super complicated, just be prepared to sweat your arse off in the attic. I bent my own sheet metal to make a box for the return grill, cut out a hole in it and the plenum, then tied the duct into both. If I recall correctly, it took me about 7 hours total, but I had a short run from the new return to my unit in the attic.

Make sure when you cut the drywall to have a vac nearby and cover anything you dont want dusty. That stuff gets everywhere when you cut into it. Also get a proper drywall saw and dont be an idiot like me and cut it with an ocsillating tool.

good luck and stay hydrated

Use a filter back return air grille unless you are filtering the air at your unit.

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bapple

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I really need to do this in my MBR. Thanks for the link to your experience here.

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Adding a R A Grille does not change the overall dynamics of the system. The unit will not get more return air; it will just get return air from another place.

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Completely inaccurate.

I don't know what the ratio is but an A/C system needs close to as much return air as it does cooled air.

When I replaced all 3 of my systems the company put extra returns to 2 of the 3 units.

Your Supply ducts and Return ducts should be sized to supply about 400 cfm of air per ton in a 1:1 ratio. So a 3 ton unit, 1200 cfm, 4 ton unit 1600 cfm, …. You can have a single return air duct or multiple return ducts as long as it provides the necessary return air volume.

Do you know the current size of your return air ducting? Is it round or square? If you have square return duct/plenum, if so then the formula L x W x 2 will determine the return air volume.

For example (actual example from my house), say you have a 4 ton HVAC, then you need 1600 cfm of return air. With a single 24 in x 24 in return air plenum with 1 in thick filter (square ducting) it would provide 1152 cfm of return air (24 x 24 x 2), so you would be short about 500 cfm of return air (when I changed out HVAC this past Feb I added a second return air duct to supply that 500 cfm shortfall on the other side of the house and it definitively has improved comfort).

You can calculate if you currently have sufficient return air volume or if you need more. The table below will help determine volume of return air supplied by various size round ducts, and as you see there is a difference between rigid and flex ducts so you size accordingly. So adding an additional 12 in dia flex return air duct should deliver about 330 cfm to the furnace/air handler.

Lastly, if you like to keep your master bedroom door closed, adding a additional return duct would help - just size it properly.

When I finally get bent over by an AC company to replace my central unit, I will add some return ducts and rigid ducts. When the AC system was installed back in the 1980’s they used a rigid flex duct every where. The insulation is actually torn off of them. Units were replaced in the early 2000’s but the ductwork is original.

I may even see if they can move the unit to an attic sideways installation to get more pantry space since the unit is vertical and takes up some needed central closet space.

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I don't know what the ratio is but an A/C system needs close to as much return air as it does cooled air.

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Adding a return air duct does not change that ratio. It merely splits the RA volume to multiple locations, but the total RA remains the same (unless you were undersized to start with, in which case you need to do it anyway).

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Agreed, but I think a 12" X 12" is preferred since the need is to move as much warm air out of the room quicker and allow the the transfer to cool air to be more rapid.

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Its not pressurized though for the most part. Its impossible to say without seeing your system for sure, you absolutely could be right. 12x12 duct is going to require a 14x14 vent or so which is pretty large. So its going to be seen. Obviously you can't really over do it here. But I was pointing out flex duct because you can get it already insulated and it will go between rafters, joists, studs, etc very easily. You'll have to plan a 12x12 in many cases.