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  1. #11
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    Jul 2009
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    Default Re: Sealing air ducts

    1. If your supply ductwork is in an unconditioned space it should be taped sealed and insulated, if in a conditioned space they should be taped and sealed but don't need to be insulated. You want the air to get where it's supposed to go, If you don't tape and seal it can leak and lose pressure within the duct.

    2. You should never put a grill directly on your supply plenum. If you want a little heat in your cellar put one in the main trunk at least 18" away from a supply run and not directly across from one. Putting a grill on the Plenum will also cause a pressure loss, the plenum also acts to make the air less turbulent.

    3. Your return does not have to be insulated but should be taped and sealed. You want to bring back the air from the conditioned spaces and not the attic or cellar.

    4. It's up to you if you want your cellar Conditioned or not but be aware that your Heat System was sized to a certain number of BTU's and it may not have included the size of your cellar. If not you would be stealing heat from the other rooms in your house, making your furnace run to long, not efficient.

    Good Luck!!!

  2. #12
    Join Date
    Jan 2010
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    Default Re: Sealing air ducts

    Many thanks for your advice, Sten!

  3. #13
    Join Date
    Jul 2009
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    Default Re: Sealing air ducts

    Your Welcome

  4. #14
    Join Date
    Jan 2010
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    163

    Default Re: Sealing air ducts

    QUOTE
    I live in very cold climate in the upper midwest. I just had an energy audit that left me so confused I can't believe I paid for it. Some of that auditor's claims were about ducts in the basement.

    First, he said the unfinished basement was too cold. He said I should caulk the old windows in the basement shut. Then I should "add a heat register to the plenum of the furnace to heat the basement space." This sounded strange.

    When I asked him about sealing or insulting the ducts, he said I shouldn't do it. (He never mentioned the ducts for the returns, which I gather are always good to seal/insulate.) He basically gave Canuck's answer. But of course Canuck was saying that you don't need to seal/insulate if the ducts are "basically in conditioned space." But if my basement is unfinished and unused except for laundry, do I want my basement to be conditioned?

    I have several other questions resulting from the audit, mostly having to do with how to cut down on air bypasses in my balloon-framed home without creating moisture problems. But these are the questions I had relating to duct sealing. Any thoughts for a confused newbie?


    It may not be critical to seal your basement ducts, but it is always helpful, if for no other reason than to make sure that the air gets delivered to spaces where you want it.

    Don't add more heat (airflow) to the basement if you don't want to. But don't take only return air from the basement if there's a water heater down there--you might de-pressurize the basement and cause the water heater to backdraft.

    Anything that the auditor suggested as regards sealing the envelope of the house is a good idea, and the one thing that will give you the most bang for the buck.

  5. #15
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    Jul 2009
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    Default Re: Sealing air ducts

    If you want the air to go where it's supposed to, seal your ducts. This not only gets the air to go to the rooms you want but maintains internal pressure whithin your Ducts which is Critical. If you don't seal them you will lose air and pressure, two strikes against your system as well as a loss in efficiency. Internal pressure is what gets the air to the conditioned spaces. I can't understand why one would choose not to have them sealed when the cost is so minimum and the gain is maximum. As for a return in an unconditioned space such as the basement in question, why would you ???
    Last edited by Sten; 01-13-2010 at 08:54 PM.

  6. #16
    Join Date
    Jan 2010
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    163

    Default Re: Sealing air ducts

    As for a return in an unconditioned space such as the basement in question, why would you ???

    Very often, there will be both supplies and returns in basements that people don't want to heat. So they close off the supplies, but not the return(s). This can lead to the de-pressurization I mentioned.

  7. #17
    Join Date
    Jan 2010
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    3

    Default Re: Sealing air ducts

    I think it's important to note how to seal your ducts. Do NOT use duct tape. You need to purchase aluminum tape which is very sticky and will mold to the connections. When you're not using the system, buy a container of latex sealer and "paint" all of the joints with the sealer to eliminate air loss.

    One of the reasons systems are over-sized is that it takes into account the loss of heat at every connection point. In days of cheap energy, this was OK, but in today's world, it's definitely a waste of money.

    In terms of your basement, you should consider insulating the basement walls with spray-on insulation. This way they can close up all the leaks on the rim joist, provide a vapor barrier, etc. Just 1" of the product is R7. I did this to my basement and you wouldn't believe the difference. My basement gets comfortable just from the radiation of heat from the ductwork when the furnace runs. I'm working on adding additional insulation with new outside stud walls, but this will be the more inexpensive fiberglass batts since my spray-on insulation provides the vapor barrier.

    Also, as noted, do NOT put a register in your main plenum. I moved into a house with these. I got rid of them all and now the rooms are being heated and cooled correctly. If you want to heat that space, spend the time and money to install proper round ductwork down to the floor. However, make sure to install a damper to adjust the flow at the point closest to the plenum. By sealing the ductwork and installing the new supply line, you'll be able to heat the basement for "free" since you've sealed up all of the leaks.

    If you insulate the basement walls and rim joists (air leaks are your worst enemy) and heating the basement, you won't have that temperature differential between the basement and upper floor, which is a better situation.

  8. #18
    Join Date
    Jul 2009
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    Default Re: Sealing air ducts

    It would be better if you use an actual duct sealing product, I'm sure that there is something out there with latex in it but the best is called Mastik and as appleguy say's using duct tape is a no no, use the foil tape. As for a Damper at your plenem it won't hurt but it is better to have a damper at each supply takeoff, this way you can balance each room if need be. No dampers in the return takeoffs.

  9. #19
    Join Date
    Jan 2008
    Posts
    10

    Default Re: Sealing air ducts

    His point is that you don't have insulation between the basement and the regular living area, and i'm guessing that your water lines are mostly in the basement. You see you need to keep the basement somewhat heated, so sealing your ducts in a basement that you do use for laundry and have water lines in wouldn't make much sense. By putting a supply in your basement it helps keep your floors not feel so cold also, that is quite common.

  10. #20
    Join Date
    Jul 2009
    Location
    Northeast
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    Default Re: Sealing air ducts

    We can beat this topic to death but there is a right way and a wrong way. The right way is to seal your ducts and run a small supply to keep your pipes from freezing if that's what your worried about, or just do what you want. Good luck!!!

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