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Sealing electrical box air leaks


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Is there a NEC-approved method or material for sealing air leaks into electrical boxes? I have seen insulators use canned foam (a gun with a metal nozzle that allows for fairly precise work) to squirt a bit of foam into the wire entry hole, from the inside. A tiny bit of foam ends up inside the box, most of it outside (and a diligent worker can scrape off what . There are other caulk/sealant materials that would probably also do the job. I have personally used thin sheets of clay to soundproof electrical boxes from the outside, before the wall was closed.

Any thoughts on this? I have a customer who is highly motivated to reduce the air leakage in parts of her house, and quite a bit is coming from electrical openings. Doing something that is not code-approved is not an option.

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The foam gaskets work great and would be a whole lot easier, cleaner and safer than squirting foam.

I agree with Scott. My house was built in the mid 80's. I could feel air entering through the receptacles by placing my hand next to them. The foam gaskets that Scott refers to work great to seal around the box.

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Hmmmm... those gaskets are uniformly regarded by energy auditors to provide little air-sealing. Here's an image of a receptacle that has a foam gasket behind it. This is during a blower door test in cold weather. You can see air leaking in and cooling the drywall, and cold air has also cooled the receptacle itself (because it has air pathways through it), but the trim plate is warmer (and nicely uniform) because it's insulated.

In spite of that, I put them in my house. They were giving away handfuls of them at the county fair, so I got a bunch.

We may end up sealing between the drywall and the box, and putting kid protectors in the unused outlets.

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If you really want to seal them: Caulk the box to the drywall, it sometimes takes a couple spins depending on how bad the cutout is. Kill the juice and hit the wire penetration with fire-stop foam. I have one of the pro guns that can leave the can on for long periods of time without drying up. Whenever I paint a new room, I always seal up the outlets and switches. If done correctly this will seal them 100%.

Here is a shot from one I did back in November.

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