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Thread: How many Cold-air return

  1. #1
    DIY Junior Member jimi's Avatar
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    Default How many Cold-air return

    I would like to know how many cold air-return opening for a 1100 sq ft house?

    I moved into a old house, used be using oil heating and last year upgraded to gas furnance with electric forced-air system. Right now almost every room in the main floor have a large opening for cold-air return at one corner and another corner with warm-air register. one each in the living room,washroom, bedroom and kitchener. The two rooms upstair have only warm-air registers, each. In the basement, one warm-air register and also a cold-air return.

    My question is, it seemed like too many cold-ar return openings in the house.? The reason I asked because my previous new house have only 3 cold-air returns. I would like to seal off some if possible when I replace carpet with hardwood floor.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Each room is good! When you close the door, depending on how it is arranged, without one, you will upset the balance unless you have one. WIll it work without them, yes, but not as well. It tends to create cold spots.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Jack of all trades frenchie's Avatar
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    The reason your old house only had 3, was to cut costs. Each room is much better.
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    Plumbing Designer FloridaOrange's Avatar
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    Default

    If you have a larger return that handles a couple of rooms, you could "seal" off a room served in the area, but put in a transfer grille setup. This would allow air exchange but it could also allow sound transfer. Some of the cheaper builders around here do that to avoid running returns to each room. If you go that route, you could put in a 90 to try to block some of the sound transfer.

    Make sure it's sized for the amount of air to transfer.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  5. #5
    Plumber jimbo's Avatar
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    First thing is you have to have enough surface area/duct cross section so the return CFM is adequate for the supply CFM. I am sure there are rules or charts for this, like fixture units in plumbing design. It is not an area where I can quote you the book, but I'll bet there is a book!

    I can tell you from a lot of observation of a lot of homes of varying ages, cost, and quality of construction: the norm around here (Southern California) is to have just ONE large return, usually in a hallway.

  6. #6
    DIY Junior Member jimi's Avatar
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    I live in Ontario Canada. They might have different building code for a cold country. What is 90 to block the sound?

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default returns

    Here, the majority of units are roof mounted and have a single central cold air return. The doors are usally cut off 1" above the floor to provide circulation when the door is closed. The more returns the better the rooms will heat and cool, but the optimum number depends on the house's arrangement.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    90 - not straight through duct...turn it so the sound will be attenuated. Helps a little, but not much. It can help block light a little, too.

    By careful placement of the supply and return ducts, you can set up an engineered air flow. relying on the gap under a door may or may not create the air flow you want. Most builders don't take the time to optimize this. Setting up the flow with dampers can be thrown off if you decide to leave a door open after balancing, so it is a crap shoot, and sometimes not worth the effort. But, recarpeting and not keeping the opening the same can disrupt what may have been done if it isn't the same height. Having a return mitigates that effect to a degree. The end goal is to provide an unobstructed return flow to maximize air distribution and minimize stagnent air...the more attension paid to this, the fewer cold areas you'll have in the winter, and hot areas in the summer.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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