Closing off central air return

Discussion in 'HVAC Heating & Cooling' started by supermattthehero, Aug 25, 2010.

  1. supermattthehero

    supermattthehero New Member

    Messages:
    78
    Location:
    virginia
    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?
  2. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    You want a return in every room that there is a supply.
  3. supermattthehero

    supermattthehero New Member

    Messages:
    78
    Location:
    virginia
    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)?
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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
  5. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    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.
  6. supermattthehero

    supermattthehero New Member

    Messages:
    78
    Location:
    virginia
    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.
  7. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    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.
  8. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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.
  9. DeweyBeach

    DeweyBeach New Member

    Messages:
    18
    Location:
    District of Columbia
    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.
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    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.
  11. DaveHo

    DaveHo Member

    Messages:
    53
    Location:
    SE PA
    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
  12. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    **********************************************************************
    combustion air ???? (LOL) I don't think so .The poster said it is in a 1400 sq ft HOUSE, not a large MALL.
    Last edited: Sep 14, 2010
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    What do you mean by the "20x20 vent is on the OTHER side of the blower"?
  14. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    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.
  15. DaveHo

    DaveHo Member

    Messages:
    53
    Location:
    SE PA
    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
    Last edited: Sep 15, 2010
  16. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    DaveHo; Yes an NG/Propane furnace, especially one in a confined area, needs combustion air. But the amount is based on the amount of BTU's the furnace burner gives out
    .Example; For a home of 1500 sq ft the size of the combustion air, for say an 100,000 btu burner, would only need approx 28" of air (6" diam pipe) at the most, not 400 inches !!!!
    Last edited: Sep 16, 2010
Similar Threads: Closing central
Forum Title Date
HVAC Heating & Cooling Lowering thermostat , how much and closing vents Dec 7, 2009
HVAC Heating & Cooling closing up my house for two months Nov 17, 2008
HVAC Heating & Cooling closing off b vent chimney Oct 5, 2008
HVAC Heating & Cooling Closing the ducts Sep 14, 2008
HVAC Heating & Cooling Closing off radiators in a one-zone house Oct 10, 2007

Share This Page