Return in wall finished with T&G pine - how?
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  1. #1
    Join Date
    Mar 2013
    Posts
    14

    Return in wall finished with T&G pine - how?

    I understand that drywall can be glued and screwed, creating air-tight "duct" in a stud bay.
    But what about wall that's finished in T&G, on both sides? Will have following return sizes (measurements are for floor sill plate cut area):
    - 2x 9x9"
    - 1x 8" round
    - ~5x 3-1/2"x14-1/2" (regular 2x4 16"OC cavity)

    Planned for low and high return with closeable grilles on each of them. Should entire height of stud cavity be an actual steel duct now? If so, how to prevent movement, banging, etc.?

  2. #2
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    The important part is that it's sealed as best as possible to the attic or where ever you don't want air comming from. I'll leave the hi-low returns alone. Personally I'd use a floor return and keep the return out of the wall if possible.

    FYI, based on the duct sizes litsed, you maximum airflow is about 1000CFM @ 700fpm, the max for a return. So 2.5 tons woudl be max, or a 60k BTU furnace.

  3. #3
    Join Date
    Mar 2013
    Posts
    14
    I have an existing furnace, Trane XV-95 with 3.5 ton Carrier AC unit. Very well insulated house (R-35 walls, R-45 roof). Cental air will be doing mostly AC and fall/spring occasional heat. Infloor heat in the winter. 2 levels x 1,600sqf each and finished basement about the same size (including 500sqf garage, 400sqf storage room, 200sqf mechanical room, 100sqf bathroom, 200sqf hobby room and 100sqf stairway footprint + lot of old rubble wall)

    Furnace has 24x24" plenum splitting to 3x 14x8" trunks (upside-down T shape off plenum):
    1st trunk (downsizing as it goes because of distance) will supply 5x 6" round ducts on the 1st floor
    2nd trunk (downsizing) will supply 5x 6" round ducts - 4 on the 1st floor, 1 to the basement hobby room
    3rd trunk (downsizing) will supply 7x 6" round ducts on the 2nd floor
    (17 registers, 1+9+7) Some of the 6" ones may actually end up being 5".

    Might need couple more returns. 8" one is a dedicated sucker for just-below cathedral ceiling on 2nd floor.

    Why ditch the high-low idea?

  4. #4
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,585
    You have approx. 1,600 CFM of RA now. I like a little more than the blower is capable of moving. The blower is probably a 4 ton (1,600 CFM). Add another 400 CFM would not hurt. Just to be on the safe side. As important: What size is the filter on the furnace?

  5. #5
    Join Date
    Mar 2013
    Posts
    14
    It's Trane CleanEffects, I think it's 24x16" or so (7" thick).
    Would you suggest upgrading blower when this one fails?

    Return plenum turns up at 24x10" and splits to 2x 14x8" (one of them branches to 2x 8" rounds, other has 1x8" branch and goes upstairs as 14x8") and 1x8" round that goes all the way to under the cathedral ceiling.

    Trane circulates in low speed all the time.
    For 53951, would you suggest ERV or HRV or ventilating dehu like Ultra-Aire?
    Bath, laundry and kitchen fans are vented outside.

  6. #6
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,604
    i would ditch the wall cavity returns , if you are going tu use it mainly for cooling a ceiling return would be fine
    We really need change now

  7. #7
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,585
    Quote Originally Posted by bammer View Post
    It's Trane CleanEffects, I think it's 24x16" or so (7" thick).
    Would you suggest upgrading blower when this one fails?

    Return plenum turns up at 24x10" and splits to 2x 14x8" (one of them branches to 2x 8" rounds, other has 1x8" branch and goes upstairs as 14x8") and 1x8" round that goes all the way to under the cathedral ceiling.

    Trane circulates in low speed all the time.
    For 53951, would you suggest ERV or HRV or ventilating dehu like Ultra-Aire?
    Bath, laundry and kitchen fans are vented outside.
    I do not know what the CFM rating is on the 25" x 16" model for your blower size, I would have used the 25" x 20". Does the "boot" that turns into the air cleaner have turning vanes? The 24" x 10" drop is barely large enough but it's a short piece of duct so ur probably okay. The 14" x 8" ducts are good for 600 CFM each. The 8" runs are good for approx. 200 CFM if they are solid duct and not flex. You need a minimum of 1,800 CFM IMHO. So, depending on where the 8" start, just add the numbers to see what you have. People count the RA grilles and try to determine the CFM. It all starts at the unit that determines if there is enough CFM.

    P.S. I also run my return air duct into the side and bottom of the furnace when I'm moving anything over 3 tons of air. I did it for my 2.5 ton system. I like to take the full effect of the filter area as well since the opening on the furnace is only 14" high.
    Last edited by George2; 03-15-2013 at 07:34 AM. Reason: made it more understandable...lol.

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