Adding another return air vent

It seems pretty high to me and likely a job a reasonably handy person can do themselves,

I was offered the same option and it was like $1k for a duct in ceiling and~40 ft of flex through the attic to easily tie in. Easy access and tie ins as well.

It was part of an initial request to add 4-6” of cellulose insulation over the whole house for like $3500, totaled $4500 and I was not expecting that.

I passed on that company and added 4-6” fiberglass insulation using another guy instead over the 2000sf for $700.

We replaced the AC at our old house, and the company charged us and additional $200 to add another return. They were obviously already up there doing other work, so it's not like they just came out to do the extra return by itself.

I have a 4 ton unit in the attic with a 3.5 ton outside if that makes sense. I currently only have a 20x20 return air vent in the hallway. My master bedroom is in the back of the house and I feel like this room is the warmest. They suggested that I add a return air vent in my master bedroom which is the farthest point from my ac unit in the house (probably a good 40 feet). I have no idea of the size of the duct that they will use.

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have a 4 ton unit in the attic with a 3.5 ton outside if that makes sense

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It does make sense - it is not uncommon to have the indoor evaporator coil slightly over-sized for the outdoor condensing unit and it doesn’t affect the efficiency of the unit.

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currently only have a 20x20 return air vent in the hallway.

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I asked just to make sure they were giving you good information on the need for a second return. They are.

You should have 400 cfm air flow per ton (outdoor unit), so you need 1400 cfm (3.5 ton x 400). Your 20 x 20 return plenum is providing 800 cfm of return air to the air handler (20 x 20 x 2 = 800 cfm). So you are short 600 cfm (1400 - 800). The 2 is multiplied b/c the 1 inch air filter in your return grill allows 2 cfm of return air per sq in to pass through. A HVAC unit can only supply as much air out the supply registers as it pulls in from the return vent(s), assuming everything on the return side is sealed properly, so you are not getting the air flow you should from the 3.5 ton unit.

Looks like they would/should add a second return vent to supply an additional 600 cfm of air to the return plenum, that would be something like the equivalent of a 18 x 18 grIll. Looks like that might be a pretty sizable duct they would have to install to move that much additional air over 40 feet from the MB to the return plenum if that is what they are basing their calculations on.

Though I don’t really know if $1,400 is a fair price for what they are proposing, it certainly appears that a deficiency of return air is likely the source of your cooling problem in your MB.

Now, this might not improve your air flow problem b/c you are Indeed short of return air supply by a good bit, but you could try adjusting the duct work dampers in the attic to try to supply some more air to the MB - that is assuming you have adjustable dampers in your ducts, most do, but not all. Your damper to your MB is likely wide open, so you would have to partially close dampers in other ducts that might be supplying more air to those areas than needed to divert more air flow to the MB.

I actually have a similar problem to yours, but not as severe. I had planned to add an additional return vent when I replaced my HVAC in the next year or 2, so I haven’t obtained a cost estimate, but I’ve done my homework on what is needed.

Indeed, air balance and duct leakage are also parts of the air flow equation which are every bit as important as return air, and those should be looked as well as adding an additional return air supply. If you need to hire someone to install the new return air supply, you might as well pay a little extra and ask them if they can balance the air flow for you and check the ducts for leakage.

Right now, with 800 cfm of return air flow your 3.5 ton HVAC is really only delivering the air of a properly deigned and balanced 2-ton system, but you are paying for 3.5 tons of cooling.

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OR 2 smaller return air vents (I think 12x12 or 12x20) added with one in my master bedroom and the other in another part of the house or possibly another bedroom.

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I would have thought the HVAC company would be in a better position to suggest the better option, but personally I would inclined to go with 2 smaller returns if one of the new returns is placed in another area of the house and not so close to the existing return and the new return in MB.

Filters are cheap and easy to change - remember the primary purpose of the filter is to keep the blower and the evaporator coil in the air handler clean - not air quality for your health - so you don’t need expensive high MERV filter, all they do is restrict air flow. I use a $3 MERV4 fiberglass filter that has minimal airflow restriction and change it on the first of the month whether it looks dirty or not. Lot cheaper to change filters than to pay for expensive equipment repairs associated with dirty components.

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I would have thought the HVAC company would be in a better position to suggest the better option, but personally I would inclined to go with 2 smaller returns if one of the new returns is placed in another area of the house and not so close to the existing return and the new return in MB.

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He did say something about adding the third return air vent benefiting the pressure? I am an idiot when it comes to any repair beyond what I can do with basic tools. The downside would be that the if the third return air was added it would either be in another bedroom which would be fairly close to the current return air in the hall or in a common area of the house that quite frankly gets cooler than the rest of the house already.

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Also try to keep doors open to all interior rooms, if there is no need to close them, which helps draw air throughout the house to the air return registers.

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Yes. I have a teenage son who pretty much always keeps his door closed. If he’s anything like I was he is in there beating off. HVAC guy suggested some kind of deal for the bottom of the door which involves cutting a small portion off of the bottom of the door.

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HVAC guy suggested some kind of deal for the bottom of the door which involves cutting a small portion off of the bottom of the door.

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There are grates you can put at the bottom of the door, grates in the wall above the door, or jumper ducts in the ceiling that pulls air from a closed room into a hallway where your return vent is located. Some cut 3/4 inch off the bottom the door to help pull air from the room when the door is closed.

But I think the important point is an understanding that for maximum cooling and heating efficiency, one must pull return air from all areas of the house to enter in air handler. Many think closing doors of rooms not being occupied will help better cool areas of the house that are occupied when just the opposite is true.