Size of intake vent?

Discussion in 'HVAC' started by Jungle, May 9, 2013.

  1. May 9, 2013 #1

    Jungle

    Jungle

    Jungle

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    If the intake is 14" x 8" to the furnace does the vent size have to be bigger? Does it really need a basin to catch air? I'd like to replace the old tin work because i think the air intake is too low and collects dust. I want to continue that same size of 14x8 intake vent and reposition the intake vent inside the stair case higher up from the floor. As it is now it is about 30" x8" which seems overkill to me and is dust trap.
     
  2. May 10, 2013 #2

    CallMeVilla

    CallMeVilla

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    Hi Jungle. Welcome to the Fun House ... I'd like to see pics if you could post them (this is a standing rule for inquiries). As I read what you said, I wonder: Is there a filter on your unit? If so, dust would be captured. You should know that intakes, feeds and returns are engineered and sized to optimize the performance of HVAC. However, simple repositioning the intake (return?) should not be a problem but reducing its size would be a problem.

    :D
     
  3. May 10, 2013 #3

    nealtw

    nealtw

    nealtw

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    If you do that you will only be using one cavity in a 2x4 wall so you would be down to 14 1/2x 3 1/2. I beleive the return should be more than the total of all the heat vents
     
  4. May 10, 2013 #4

    Jungle

    Jungle

    Jungle

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    The thing is the tin work was installed 30 years ago and i have upgraded the with new hi-eff furnace. There is a filter of course but that is the problem too much dust getting in there. The 30"x 8" intake is beside the stairs and uses the space between the joists in the basement as the basin, i think it is drawing some air from the basement too, so i want to rebuild the whole thing. I don't see the point of this basin, is it necessary?
    If the intake is 14" x 8" then continue the vent up through the floor, long as it is not smaller then okay right?[​IMG]
     
    Last edited: May 10, 2013
  5. May 10, 2013 #5

    nealtw

    nealtw

    nealtw

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    I'm not a HVAC guy so take it for what it's worth. Not sure what you mean by basin. They use the cavities between the studs or floor joists as duct work so to calculate the square inches you measure the cavity. So the grill and the cavity should be simular size to the intake at the furnace. If you are shortening the run and making it have less corners you will increase air flow.
    Not sure if anything here will help for dust, as your filter is at the furnace some dust will alway collect in these areas. If you have heat registers in the basement, there should be a return from there.
    I hope some of that helps.
     
  6. May 18, 2013 #6

    keepinitcool

    keepinitcool

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    I take it this isn't the only return air for the furnace? You need to have the same square inches of return as you do of supply. So say you are bringing 2 6" runs into your bedroom, this calculates to around 56 square inches of supply. You need 56 square inches (or preferably more) of return. I would put a 8x8 return (64 sq in), or a more common size 10x8 (80 sq in) in that room. So to answer your question, a 14x8 return (112 sq in) would be sufficient in a room being supplied with 3 6" runs, 2 8" runs, 2 6" and 1 8" run, 1 10" and 1 6" run, 1 10" run,
    1 8" run, 1 6" run, and so on down the line. Keep it the same or more. To find square inches of round duct take the radius and square it and multiply it by pi (3.14). 8" round would be (4x4)3.14=50.24 square inches. Hope this helps you out!
     

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