Closing off central air return

**supermattthehero** · 08-25-2010, 07:57 PM

I live in a single-story 1400 sq ft home on a concrete slab. Every room in the house has at least one supply vent, and one return vent. In the office, however, there is also a large 20" x 20" return vent which is on the other side of the main blower for the system. As a result, this return vent is VERY LOUD while running, and makes phone calls ifficult.

Is there any reason I cannot close off this 20" x 20" return vent since every room has at least one 7"x11" supply vent and one 7"x11" return vent?

**dlarrivee** · 08-25-2010, 08:15 PM

You want a return in every room that there is a supply.

**supermattthehero** · 08-25-2010, 08:20 PM

Originally Posted by dlarrivee

You want a return in every room that there is a supply.

And indeed there is. But what about the noisy 20"x20" return vent in my office (in addition to the supply and return vents already present)?

**jimbo** · 08-26-2010, 06:52 AM

In general, you need to maintain balance on supply and return. A 20 X 20 is a pretty good size return,and I have seen homes about your size with only one return, and it is about 20 X 20. If there is that much air noise on that return, I would investigate restrictions, either on that one, or other returns ,or something going on in the ducts

**gator37** · 08-26-2010, 07:32 AM

You really need to verify how much cfm is being returned by your return vents before you block it off. You can try blanking it off with a piece of thin plywood behind the large return grill but watch you evaporator coil for freezing (lack of air acrossed the coil) and listen to your bedroom returns for noise.
In very general terms you can figure 400 cfm per ton
Other options are to relocate it on the otherside of the wall (if you do not have a door on your office) and the new location is in the living room or hall, or you can extend it to the other side of the room it is located in now and internally line the duct with insulation.

**supermattthehero** · 08-26-2010, 08:22 AM

But if the supply and return must be balanced, and in every room there is a 7x11 supply and a 7x11 return, then why do I still need a 20x20 return? I have blocked it off with plywood, and it responds simply by pulling more suction from the smaller returns in each room.

I tested it by taking a piece of toilet paper and holding it up to one of the 7x11 returns. It did not stick. Then I blocked off the 20x20 return, and the toilet paper did stick. Does this sound OK for blocking off the 20x20 return then?

Thanks for all of the responses.

**Hube** · 08-26-2010, 08:45 AM

Originally Posted by dlarrivee

You want a return in every room that there is a supply.

That statement is not correct. You do not want a return in the bathroom or the kitchen areas. Having a return in these areas simply sends any odors thru out the rest of the home.

**jimbo** · 08-26-2010, 07:27 PM

When I said balanced, I did not mean that every room had to match the others. The ducts and distribution are sized for the different square foot area of the different rooms. Broadly speaking, each room needs to have the same CFM returning as enters the room. Your TP test seems to say that there is too much return from the office and not enough from the bedrooms.

**DeweyBeach** · 08-30-2010, 02:35 PM

Some systems do not have returns in every room, only one or two main returns in a central area. Return air from each room should (in theory) find its way to the return duct under doors, etc.

**jadnashua** · 08-30-2010, 02:46 PM

Unless there are no doors, a return in each room will provide the best comfort. True, they aren't installed that way very often. Take a bedroom with carpeting on the floor and the door is closed with little gap and no return...the room will be warm in the summer and cold in the winter if you can't move the air properly.

**DaveHo** · 09-13-2010, 11:38 AM

What type of heating system do you have? I might be wrong, but based on how loud you say it is & other systems I've seen it sounds like this 20x20 grill isn't really a return, but a source of combustion air for the furnace.

-Dave

**Hube** · 09-14-2010, 12:39 PM

Originally Posted by DaveHo

What type of heating system do you have? I might be wrong, but based on how loud you say it is & other systems I've seen it sounds like this 20x20 grill isn't really a return, but a source of combustion air for the furnace.

-Dave

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combustion air ???? (LOL) I don't think so .The poster said it is in a 1400 sq ft HOUSE, not a large MALL.

hj · 09-14-2010, 01:51 PM

What do you mean by the "20x20 vent is on the OTHER side of the blower"?

**Hube** · 09-15-2010, 07:33 AM

most homes in the 1500 sq ft range on 1 floor may require 240-300 sq inches of RETURN AIR, but you say you have a 20x20 along with several others sized at 7x11. That means you could have total of approx 800 sq inches of return air !!!! Something is amiss here. You would be best to bring in a pro for a "hands-on" look at your situation.

**DaveHo** · 09-15-2010, 08:36 AM

Originally Posted by Hube

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combustion air ???? (LOL) I don't think so .The poster said it is in a 1400 sq ft HOUSE, not a large MALL.

Why not? House is on a slab, so the furnace is on the main floor, probably shoved in a small utility closet. If it's not a high efficiency furnace it will need to draw air for combustion from inside the house. So either the door needs to be lovered, or there needs to be a grill in the wall. This is a pretty common setup in these parts, when you have a NG/Propane furnace.

-Dave