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Condensation Question

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  • Condensation Question

    I live in Michigan. I built and moved into a brand new home in November of 2005. We are going through our second winter in the home. We are preparing to finish the basement and I noticed something last night that I have a question to ask the forum.

    I have been sealing the sill plates and rim joists around the entire basement, and I am also in the process of replacing all the R-13 insulation that the builder installed between each joist along the perimeter of the basement. When I got to the 2 fresh air ducts plumbed to the outside of the home (the first one supplies fresh air to the area of the furnace) (the second one supplies fresh air to the return duct work), I noticed that ice is building up on and around the metal duct work that is stubbed into the home. Flexible & insulated duct is connected to the metal duct work and is plumbed to each area described above. I also found ice on rim joist, and because the warm basement air is coming into contact with the area, I also noticed some small water droplets on the pressure-treated sill plate. The insulation that was installated around the duct work was damp/wet, not soaked, and basically was only wet around the circumfrence of the duct.

    My question is if this is a common occurrence here in Michigan, especially with the cold weather we are having, if something was done wrong, or even better yet if there is a way to correct this problem because I worry about mold and the like.

    Thanks for the help in advance!

  • #2
    Re: Condensation Question

    s70: I doubt that anything was "done wrong". Condensation (in your case, ice) forms when warm moist air comes in contact with cold metal pipe. Your solution is to seal off the area where the pipe from outside comes into the basement from the warm air of the basement. The seal should be air tight. Or, you can insuate the pipe from the joist to where it connects to the flex pipe. Here again, it should be air tight.
    Jim

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    • #3
      Re: Condensation Question

      Jim,

      Thank you for taking the time to write me back.

      Can you please explain in better detail how to achieve an air tight seal around the fresh air inlet ducts coming into our home.

      As previously described, we have 2 metal fresh air inlet ducts coming into the home, plumbed through the siding, ridgid insulation, and the rim joist (which is made of plywood). I filled and sealed the gap between the hole in the plywood rim joist and fresh air inlet ducts with silicone caulk. Once dried, I re-attached and secured (with cable-ties) the 6-inch insulated flexible duct (which I think has an R-6 rating) to the ridgid duct pipe entering the home. Once the flexible ducts were re-attached, I re-installed the kraft faced insulation (which is now R-19) with the vapor retarder facing towards the exterior of the home.

      I just checked out each area again last night, and have the same problem...ice and moist/wet insulation around each duct.

      Thanks again in advance for the assistance.

      Comment


      • #4
        Re: Condensation Question

        s70;
        First, the vapor barrier on your R19 insulation should be facing the interior of your house, not the exterior. Second, cover the joist space the duct is in with plywood, sheet rock, or any material that will completely seal off any air that may get at it from the basement. You do not have to seal off the whole joist area, only back a couple of feet on to your insulated duct. Be sure to seal aound the duct so no air can get to the place where the duct comes through the wall. If warm moist air cannot get to the cold pipe, you will not have condensation on it.
        Jim

        Comment


        • #5
          Re: Condensation Question

          Originally posted by s70jeric View Post
          I live in Michigan. I built and moved into a brand new home in November of 2005. We are going through our second winter in the home. We are preparing to finish the basement and I noticed something last night that I have a question to ask the forum.

          I have been sealing the sill plates and rim joists around the entire basement, and I am also in the process of replacing all the R-13 insulation that the builder installed between each joist along the perimeter of the basement. When I got to the 2 fresh air ducts plumbed to the outside of the home (the first one supplies fresh air to the area of the furnace) (the second one supplies fresh air to the return duct work), I noticed that ice is building up on and around the metal duct work that is stubbed into the home. Flexible & insulated duct is connected to the metal duct work and is plumbed to each area described above. I also found ice on rim joist, and because the warm basement air is coming into contact with the area, I also noticed some small water droplets on the pressure-treated sill plate. The insulation that was installated around the duct work was damp/wet, not soaked, and basically was only wet around the circumfrence of the duct.

          My question is if this is a common occurrence here in Michigan, especially with the cold weather we are having, if something was done wrong, or even better yet if there is a way to correct this problem because I worry about mold and the like.

          Thanks for the help in advance!

          Having just read your problem and your approach to solving it. As I understand it you have a Fresh Air run connected to return air side of your heating system and a Combustion Air Drop into the mechanical room to provide enough air for the furnace and hot water tank to run properly. These are both connected directly to the outside of the house with metal hoods. Both these runs are done with metal pipe. You are well sealed at the wall but you stil have moisture or condensate at your sills. Only happens when it is cold. Both the fresh air and the combustoin air are a direct link to the outside. You have a metal hood connected to a metal pipe coming from a freezing outdoors into a heated basement with no thermal break. The cold air and the warm air meet at the hood and as warm air meets cold it will condense and moisture will form and possibly freeze. Same idea as windows icing up on cold days. There are ways to help prevent this. 1) replace your outdoor hoods from metal to a plastic. 2) Replace your insulated metal pipe on both your fresh air and combustion air with an insulated flex pipe of the same inside diameter. You have probably notice that in your furnace room for your combustion air it is always draughty (Cold air drops) There are 2 approaches to help solve that 1) which you may have now is to have your pipe terminate into a Combustion Air Bucket. 2) to have a Hoyme damper (this is a product name you may have something diff. in your area) But it is a moterized damper that opens and closes as the furnace calls for heat and tha way you do not have air continually dropping into the mechanical room. It is very important not to block of the comb. air into the furnace room. If you do under the right conditions you could have backdrafting of you hot water tank and /or furnace bringing exhaust gases back into your house. Hope this helps you out.

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