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autx790 06-13-2011 01:53 PM

Return air grill size, location, construction
I am trying to move the return air location for my house to make room for stairs (converting a duplex). I basically want to move it across the room into what will be the pantry, but trying to minimize the space it will take up. I have a 3.5 ton unit for about 1050 sqft and before the filter they were using was a 14x24. I have the old air return duct under the house but it's very large and I don't really want to run that up through the floor in the pantry. I'm thinking i'll need a larger filter (20x20 or 24x24 or something in that range) but not quite sure how to build the return box or the best way to run ducting to it to minimize the space it takes up. Where I'm trying to put it is roughly the center of the house. Any suggestions on placement, size, box construction? I'll try to include some photos later.

Marty S. 06-13-2011 07:06 PM

3.5 ton(way oversized for 1050 square ft) should be 1400 cfm. Filter should be 350 fpm so 4 square feet or 576 square inches.

autx790 06-14-2011 08:13 AM

Thanks Marty! Not sure if this makes a difference but I got it wrong. It's a 3 ton, not 3.5. Goodman...gph1336h21ac. Does that change things much?

Technow 06-14-2011 11:42 AM


Originally Posted by autx790 (Post 667107)
Thanks Marty! Not sure if this makes a difference but I got it wrong. It's a 3 ton, not 3.5. Goodman...gph1336h21ac. Does that change things much?

No, way too big, who determined the size of that thing?

autx790 06-14-2011 02:49 PM

Haha, who knows! Whoever put it in, also didn't seal around the registers, so upstairs i'd get the occaisional rat poo falling on my bed (and elsewhere), nor did the seal up the return box, and the drain for the pan was all wrong so that was basically a pool for the rats to lounge in.

Should I try to sell the unit and buy a smaller one? I'm not sure what the size is for the upstairs unit (it's smaller i'm pretty sure)...i'll check. But the upstairs is only about 800 sqft and I cant really cool it less than 86 degrees during the summer. If I set it on 86 it will run non stop for a few hours in the day. Of course I have to take in to some account that the downstairs unit is not running, but it's been like even when the upstairs and downstairs were seperated (duplex).

autx790 06-14-2011 07:47 PM

2 Attachment(s)
My upstairs unit is a heat pump

I don't know much about HVAC so i'm not sure how that relates.

autx790 06-20-2011 11:23 AM

I'm probably going to get someone to come out and check out my systems to get serviced and/or see what I should do. If this unit is oversized, and all the supplies are already run to it, would replacing this unit my self be a good idea, or is it better to have someone else?

COLDIRON 06-20-2011 05:16 PM

Look up return air floor/sidewall registers they are about 30" long by 10/12 inches high they sit right on the floor and stick out of the wall about 3inches at the base. What you do is cut a long 30" hole in the floor by about 21/2" out leave all joists don't cut them. In the basement you have to figure out where this spot is before you start and duct to it or pan(sheet metal plates) over to it and tie it in at the basement. It's hard to explain if you never did it. Maybe someone else can explain it better.

autx790 06-21-2011 07:51 AM

Thanks Coldiron. I can't seem to find what you're describing by searching the internet. The only thing I can ever find is the grills. So i'm not sure if HVAC guys just make up their own boxes or if you can buy assembled units, or what you're referring to. Do you have a link to one?

COLDIRON 06-21-2011 09:12 AM

Just go on line and look for baseboard return air grilles. They sit right on the floor, you can cut the baseboard so it fits right against the finished wall. It is shaped sort of triangular with the bottom wider than the top.
Check Reilly you'll find them

autx790 06-21-2011 10:58 AM

Thanks...i found one...

Seeing as how this is only 3.5" thick, I could just put a regular box framed into the wall cavity, couldn't I? I have true 2x4 construction. It just doesn't make sense to me that you could have a grill that needs to be 14x24, or whatever, but then have it 4x14 feeding to the bigger duct. Seems like your airflow would be limited to that smalled dimension.

also still not sure if it's worth it for me to downsize my unit or just leave what I have.

I think i'll probably just have someone come out and hope i get someone better than the guy who did the first installation

COLDIRON 06-21-2011 11:55 AM

That's it. You don't cut out the wall or make a box up stairs all you do is cut the baseboard out to the length of the grill then cut the floor out(to the basement) say a 1/4 in less than the grill sticks out leave the floor joists in place just cut around them. Install the grill then go to the basement and pan sheet metal from the return duct to the hole and close it off with end caps so the heater unit will draw air from the conditioned space. You need to really look things over and think about where the grill location will be in relationship to the return air in the basement but generally that is how it's done.
So when your done cutting the hole it will be approximately 21/2 " by 30" long. Just a guess on the size grill depending what you need for RA to the unit. It"s hard to explain if you have never done ductwork before.

You can even install smaller ones throughout the house if you need more return but they all must tie into the main RA trunk line.

autx790 08-08-2011 01:24 PM

So I'm still working on this situation (among other things) and decided to get a quote to see if it would be worth it to hire out the job. The quote I got was about $2800, but that would be to run all new duct work. Is that reasonable and worth the cost to just get it all replaced or should I just attempt the install my self? The company is highly reviewed on google so I trust they'd do a good job. Just not sure if it's worth a redo if all I really need is a return hooked up and ducts run into my bed/bath/closet/laundry area.

As for the oversized unit, I think maybe they were taking into account the house was built in 1839 and each room has 3 or 4 large inefficient windows/doors as well as no insulation (i've put new insulation in).

REP 08-09-2011 02:28 AM

In my neck of the woods that price would be considered too low to make a profit on.
In my neck of the woods it would be double what you have been quoted.
But I'm sure that you won't get a manuel "J" or a manuel "D"
These two calculations are woth more than any quote for equipment unless you are rich enough to pay extra each and every time the unit kicks on for the next twenty years.

autx790 08-09-2011 06:41 AM

No I dont think he'll be doing any calculations. He just plans on tearing out all my duct work and installing new lines. What gets me though is the current duct work is only 4 years old, but hasn't been used for about 2.5 of those years. The current main return and supply lines are (I believe) 18" and are laying on the ground, and this guy plans to replace those with sheet metal ducting, so that could be nice. Thanks for the feedback!

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