GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Blower Door Test Obvious Leaks

Salesi | Posted in General Questions on

My county requires a blower door test as part of the inspection process. I would have one done even if it was not required. I have been pretty meticulous about sealing the house: zip sheathing, Prosoco caulk to seal between the zip sheathing and foundation, sealing the windows, taping the electrical boxes, etc. Are there any other obvious places to look and seal before the blower door test is done? I am thinking about sealing the conduits at the distribution panel in the garage since they are connected to the house. Not sure what other areas to look for. I would like to get the air changes per hour as low as possible. Thanks for anyone’s help.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    BILL WICHERS | | #1

    If you have an attic hatch, make sure it's sealed too. That usually means a good gasket and a latch that will hold it tightly closed.

    Any/all penetrations through the building envelope are the first things to seal. It sounds like you've gotten most, but check everything: hose bibs, utility wire entrances, etc.

    I wouldn't seal conduit entries into an electrical panel. You don't want sealants INSIDE that panel. I suppose you could tape the cover, but I've never done it. I have, on occassion, and usually to prevent sound transmission, stuffed a length of fat backer rod into conduits to close up the air space inside. I doubt this is technically an "approved" method, but it works. Note that I've only ever done this on communications conduits (specifically with intercoms, use conduits like speaking tubes and carry suprisingly loud sound levels over suprisingly long lengths of conduit). I'd be reluctant to try it on a power circuit without making sure your electrical inspector would be OK with it.


    1. charlie_sullivan | | #2

      You would know better than I, but isn't electrical duct seal putty made for exactly that purpose?

      1. Expert Member
        NICK KEENAN | | #3

        Bill can answer better than I, but I think he's talking about sealing the inside of the conduit, the putty is made for sealing between the conduit and the hole in the wall it goes through.

      2. Expert Member
        BILL WICHERS | | #4

        It's not really "electrical" duct seal, but yes you can use that -- I'm just not a big fan of that material. Duct seal tends to harden with time (don't believe the "non hardening" mumbo jumbo on the label), get crumbly, then fail. I use it sometimes around the exterior of pipes/conduits, but I don't like it inside where it is harder to inspect and service. Duct seal is also difficult to get a good seal with when there are multiple small wires in the conduit.

        You could use Polyseal, but it's not recommended for smaller conduits.

        The best options are expanding cable grommets, but they're only available for small numbers of relatively large cables. I'm sure someone is making a foam insert, but I couldn't find anything like that when I looked.

        If you need a temporary air seal, you can try using duct seal, just keep it neat and dont't stuff too much inside the conduit. I wouldn't trust this material long term.


        1. charlie_sullivan | | #5

          Thanks for that helpful explanation.

          When you say Polyseal, are you meaning the sealing products from the "polywater" company? I just took at look and they have a new-ish product specifically for smaller conduit, 3/4 to 1.5"

          But I'm not very enthusiastic--it looks messy, expensive, and hard to remove.

          I always assumed that the reason for putty vs. spray foam was to avoid thermally insulating the wires. I guess that's not a big deal if it's only a few inches of wire length, since the heat can conduct along the wire.

          1. Expert Member
            BILL WICHERS | | #6

            Yes, that is the Polyseal stuff. It's like an extra tough version of canned foam intended for sealing conduits.

            I mostly use these sealers in my commercial work on telecom systems. We have to seal underground ducts so that they don't carry water. If you look online, you can probably still find some information about the Verizon switching sites in New York that failed in the hurricane of 2012 because sea water came in through the underground ducts and flooded the lower levels of the building where the power systems were. I personally had a 4" conduit in a building that was siphoning water from somewhere, and it was, um, "fun", trying to seal that while water was flowing into the building's boiler room...

            The foam sealants are difficult to remove, that's true, and it's one of the reasons I don't like them for serviceable things. I don't normally seal the interior of smaller conduits in things like electrical panels at all. The nice thing about using fat backer rod, even though it's not technically listed for this purpose, is that it's very easy to remove and it doesn't make a mess. Fat backer rod works pretty well in 1/2" and 3/4" conduits, which are the most common sizes you're likely to see at smaller sites and residential buildings. For 2" service entrances, you can probably find one of the sectional expanding rubber cable grommets that tighten with a central bolt. These grommets are MUCH nicer to use, and they're easily removeable if needed.


          2. charlie_sullivan | | #8

            Thanks for the additional advice and the "fun" story.

    2. Salesi | | #9

      FYI I recevied a 1.499 ACH after the blower door test was completed this morning without sealing anything additional so I guess I am happy with that. I was hoping for less than one ACH. The only real expense was the Zip system sheathing and tape. Foaming and caulking was a minimal cost - a few hundred dollars at most. My wife did the foaming and the caulking. We built the house so I never did anything that I did not ask the question how am I going to air seal this. So with that it mind, I beleive we did ok.

      1. user-723121 | | #10

        You will get very good performance at 1.5 ACH50, under normal conditions there will be minimal infiltration for this house. What are your ventilation plans?

  2. mathiasx | | #7

    If the garage is attached (it sounds like it is), everywhere between the house and the garage.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |