re: Adding another return air vent

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If you need some 10" flex duct, I have 3 rolls that are 25' each. Those cost around $70 each, but will sell them to you at half price. They were extra from my guest house build. You can buy the connecters, intake grill and tape at Colburns in Baton Rouge.

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I appreciate it but I will not be attempting to do this on my own. I will be paying an HVAC guy to do this for me.

I just came across this return air duct sizing chart which might be helpful on adding additional return air ducts to your house. LINK

This charts shows you’d need 16 inch flex duct to provide at least an additional 600 cfm or return air or 2, 12 inch flex ducts. I’d be interested in knowing what size return air ducts the HVAC firm is quoting you on.

I may just take fish’s advice and add my own extra return air duct - I’m about 400 cfm return air short on my 4 ton system. I need 1600 cfm but have a little short 1200 cfm of return air capacity on a 24 x 24 return air grill.

I just finished adding a return vent to my unit. Fortunately my unit is in a closet and borders the hall on one side and living room on an adjoining wall. My only return air vent was 20 x 20 and was in the hallway, and I cut a hole in the adjacent wall and added a 12 x 24 vent.

The unit is a lot quieter now. The return air vent would whistle as it struggled for air with the one vent.

Cost about 30 bucks for the vent and a couple of hours for the install. No additional ducting was needed.

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I have an air return in every room of our house. AC company says ours is the most “unique” set-up that they service...I don’t think he means that in an enduring way

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So that's the way a lot of the homes here in PA are set up. I have a small return in every room except the bathrooms. One main filter before the return duct goes into the furnance/AC coil. I never saw it until we moved up here a few months ago but man its a lot better than the one huge return grate I've always had down south.

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don’t get putting in a return air at the furthest part of your house. That doesn’t make sense to me. Logically you’d want it near the other return air or at close to the supply plenum. If it were me, assuming you have the room, I’d put another return air very close to the original then tie into the plenum. If you’ve relatively hand it would be a pretty quick job. Whoever put in your unit with only a 20x20 return air screwed up big time.

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In order for the HVAC system to function properly and effectively cool all areas of the house equally, air must be pulled from all areas of the house to the return plenum - sometimes that is difficult if the air return plenum is not centrally located in the house (which it is often not as people don’t want a return plenum grill located in a central living room, dining area, etc), or if hallway, bedroom, home office or utility room doors are kept closed. So more than one return air duct might be located in different areas of the house to more effectively pull return air from all areas of the home to the air handler to be cooled or heated.

Also, when supply registers provide cool air into a closed room without a return air register in the same room, the room is under + air pressure and some cool conditioned is forced outside - the leakier the building envelope the more cool air is forced outside. If a return register is placed in that same room, sized at an equal cfm to the supply register, the room is under neutral pressure and you don’t lose conditioned air to the outside or attic. And the opposite is true, a room with a return register, without a supply register, will be under negative air pressure and thus some non-conditioned air from outside or the attic will be drawn into the house. That is the reason some houses are built with with balanced (cfm) supply and return air ducting/registers in each conditioned room. That is the ideal scenario, but more costly, which is probably the main reason it’s not done more often.

But I’ll agree, if the existing return air supply is under-sized and insufficient return air is not being supplied to the HVAC it would better to add an additional return air register to the unit even if located right next to the exiting return register than to not add one at all.

And I’ll close by saying all this assumes that only the return air ducting is undersized and not the supply ducts. If the supply air ducting is also undersized for the HVAC tonnage, then adding additional return air ducting to the system may not make any difference. This is pretty easily checked by HVAC technicians by measuring static pressure of the system at the air handler on both the return and supply side, getting a total external static pressure and comparing the cfm air flow to the HVAC manufacturers air handler blower performance charts. I’ll bet dollars to donuts the OPs HVAC tech didn’t do this, but it’s one of the first things that that should be checked when a homeowner is experiencing an air flow related cooling/heating issue.