Every time we get someone out here to look at our electrical usage or our A/C system, they all remark that we don't have enough return air for our system. We have, now, two return air vents, each 12x36.
When the house was built, it only had the one 12x36 vent in the hallway. I added the second one, in the pass-thru room, when we got a new A/C system at some point. I had to move the electrical outlet to the side, to make room for it.
But the last two times someone looked at it, they both said it needed more return air. Looking under the unit at the space that is there, there is only one more place to add another return air vent -- in the 3rd wall under the unit, in the pass-thru room.
This wall is shorter than the other two and we can only fit a 12x24 or 12x30 vent into it. After checking, the 12x24 size is much more common, so it will be easier and cheaper to get a filter to put in it, if we want to, so we decided to go with a 12x24 vent at the bottom of the wall in the pass-thru.
We started by making a cardboard cut-out the size that we wanted and pinned it in place, to get a sense of what it would look like.
Then we cut a hole to match that into the wall.
There are two walls to cut thru, the outside one in the pass-thru room, and the inside one that goes under the A/C system. There was the possibility that there might be an electrical cable in the wall, but cutting carefully the wall in the pass-thru room showed there was no cable, just some insulation, a 2x4 stud and the framing for the raised floor for the A/C closet.
Our goal is to mimic the style of the other two vents, so we remove the baseboard and the bottom part of the 2x4 stud, and cut thru the inner wall to the return air chamber.
At this point, we need a frame of 1x3 oak around the vent to match the other vents. We know from putting the second vent in, that I don't have the skills to do a good job of that, so I hired a trim carpenter to do that -- Josh Dickson from Meadowview Construction to do the frame and baseboard. He also installed a 2x4 header and support on the left side of the opening I had made for the vent.
and then to install the trim around the hole.
and the baseboard on the left and right.
At this point, I noticed that the vent has a 3/4 inch lip of metal all the way around, to support the air filter, so the opening is not actually 12x24, but only 10.5 x 22.5. The wall that we go thru is a 2x4 stud plus 5/8 or 3/4 sheetrock on both sides, plus the baseboard, or in our case the 1x3 oak trim, so it is some 6 inches deep. The return air grille sits on the outside of the 1x3 trim and is only 1 inch deep. That leaves about 5 inches of space before we get to the return air cavity itself. Instead of leaving this rough, exposed edges, I decided to trim it off with a 1x6 piece of wood, all around the opening, fitting right up to the return air grille. This was sanded and given two coats of polyurethane.
Installing the return air grille (purchased from Amazon, $49.88 before we started any work) finishes this task.