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Community and Q&A

Exterior Penetrations – Air Sealing – Best Practices

Kopper37 | Posted in Mechanicals on

Beyond the big penetrations (like windows and doors and attic hatches), I’d like to hear / see how builders are dealing with the smaller penetrations in the envelope.

Using a can of spray foam is tempting, but I don’t think it’s necessarily the best choice.

How do you effectively seal these?

* Electrical meter base / service panel conduit

* Exterior receptacles

* Vent stacks

* HVAC line sets

* Ventilation hoods

* Hose bibbs

I’ve seen some interesting methods on this site and others. Examples would be use of a DWV roof flashing boot at the attic ceiling level, to seal vent stacks . . . or EDPM sheet rubber for pipe penetrations on exterior walls.

If you have experience building exceptionally tight houses, please share with words or photos.

Here is an example:


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  1. GBA Editor
    Martin Holladay | | #1

    I assume that you are familiar with these products:


    Kaflex patches

  2. user-757117 | | #2

    I like the sheet EPDM (or neoprene) approach. I'm betting it'll be a longer-lasting airseal than what sprayfoam will provide.

    I noticed on the "Quickflash" instructions that they recommend taping their product to the WRB...
    Seems ok if the WRB is your air barrier (hopefully not).

    If you have airtight sheating, I would try to integrate the seal to the sheathing and then weatherize the connection in some other way.

  3. user-757117 | | #3

    I thought I'd add that site built seals can be done at less expense than store-bought.

    I recently bought a 4'x4' sheet of neoprene from a local industrial supply shop for $4.
    That should be enough to make seals for all my penetrations.

  4. Kopper37 | | #4

    Thanks for the responses.

    Martin - I'm familiar with those products, although I don't have first hand experience using them. I was hoping somebody who had used these, or something similar, would give their experience.

    Lucas - I purchased some EDPM sheet rubber a while ago. Like you, I figured it was a better bargain then the proprietary flashings / seals. Also, since I could cut any size hole, it seemed like I could make it work for just about any penetration (don't have to order based on a specific diameter or configuration).

    Simple shapes - like a vent stack - are easy. But line sets don't conform well, nor do electrical outlets (especially when placed on furring strips).

    For the electrical service entrance, the outside of the conduit is a no-brainer. But I'm getting conflicting information on the inside of the conduit. I'm going to purchase some duct seal, see if the local utility will allow this between the meter base and the service panel.

    It's another product I've never used, so I don't know how well it will perform:

  5. user-757117 | | #5

    But I'm getting conflicting information on the inside of the conduit. I'm going to purchase some duct seal...

    What conflicting information are you getting?
    I'd be interested in hearing how the "duct seal" works.

    I've also been thinking about insulated pipes running to and from solar collectors...
    Are you putting in any solar thermal?

  6. Kopper37 | | #6

    The house will have an underground service connection, with direct burial cable. I'm told that the local utility will place the cable in conduit when it gets close to the house (20' or so), and that they will seal this transition to keep out soil, insects, etc.

    The NEC requires a seal on the incoming raceway / conduit, to keep out insects, mice, etc. . . . but also to prevent moist air from entering the electrical cabinet, condensing on components, and causing degradation of the connections.

    But the utility's seal won't keep air leaking into the meter base from entering the conduit that leads to my service panel. That's why I'm hoping to use the duct seal. However, nobody I've talked to has heard of using it at the service panel entrance, and I've been warned about heat build-up in the conduit (vague safety concerns). It's hard to get a straight answer . . .

    I'm not planning to use solar thermal. Right now I'm searching for a heat pump water heater, which should work well in this climate (for most of the year the cooling and dehumidification will be a benefit). I'm hoping to use the Airgenerate integrated unit; unlike other models, the exhaust can be ducted to another room. I plan to dump the exhaust into the kitchen, right above the refrigerator.

  7. Kopper37 | | #7

    Lucas - I've attached a couple of pictures of the applied duct seal.

    The local electric company allowed me to install the sealant inside the meter base / service panel conduit. The sealant is like a stiff dough. I had to preheat the material to make it easier to manipulate.

  8. user-757117 | | #8

    Daniel, thanks.

    It looks good.

  9. wjrobinson | | #9

    Have used duct seal for thirty years. All electric penetrations and yes AC line sets. Great stuff.

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