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Old 11-24-2019, 05:45 PM   #1
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Air sealing around electrical boxes/outlets


Seems like there are two air leak areas when it comes to electrical boxes behind drywall.

1. through the knockouts
2. between the drywall and the front of the electrical box. Unless the front of the box is sealed to the drywall, in the winter, warm room air can slip past the sides of the box and into the wall cavity.

How do you guys get electrical boxes air tight?

I found this product called Box Shell, which is just cardboard pre-cut to fit around the electrical box, and then you fill it with spray foam.

Youtube video showing how the box works:

Seems like an effective and efficient way to achieve an airtight seal, but open to other ideas.
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Old 11-24-2019, 07:17 PM   #2
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Re: Air sealing around electrical boxes/outlets


Foam insulation gaskets

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Old 11-24-2019, 07:30 PM   #3
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Re: Air sealing around electrical boxes/outlets


Electrical boxes in a wall are similar to Belly Buttons, there's innies and outties. If cold air is coming into the room through the box it's originating from somewhere else. If air is going out of the box it's exiting somewhere else. Look at the big picture to stop the air flow. In my opinion, attempting to seal those boxes is similar to placing a Styrofoam cover on a hydrant on the side of the house to prevent freezing.
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Old 11-29-2019, 02:42 PM   #4
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Re: Air sealing around electrical boxes/outlets


I used to seal all holes and joints with caulk, can foam, foil tape, but now i think that was waste of material and effort. Should have sealed the exterior sheathing against air and forget the boxes. If plywood, just the joints and 4 sides of the stud bay. If 1x boards, 1/2" foam board. If retrofitting, with those plastic boxes, caulk at the cable openings.
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Old 11-29-2019, 04:06 PM   #5
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Re: Air sealing around electrical boxes/outlets


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Originally Posted by carpdad View Post
I used to seal all holes and joints with caulk, can foam, foil tape, but now i think that was waste of material and effort. Should have sealed the exterior sheathing against air and forget the boxes. If plywood, just the joints and 4 sides of the stud bay. If 1x boards, 1/2" foam board. If retrofitting, with those plastic boxes, caulk at the cable openings.
The stud bays are sealed - foam board cut to fit each bay with spray foam around the perimeter, and caulk where the studs meet top and bottom plates.

So the concern isn't so much about outside air getting into the stud bays (though of course that could happen over time), but about room air getting into the stud bays, which would be an unnecessary loss of conditioned air, but also a potential condensation concern in the winter since the bays are air sealed (i.e., warm humid interior air gets into stud bay and has no drying path to the exterior).
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Old 11-29-2019, 04:19 PM   #6
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Re: Air sealing around electrical boxes/outlets


How many inches of drywall didn't get sealed to the top of the top plate? Calculate every exterior wall 1 side and every interior wall both sides that cold attic air can travel down to those electrical boxes, switches and or out into the room at floor level.
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Old 12-11-2019, 03:16 PM   #7
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Re: Air sealing around electrical boxes/outlets


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How many inches of drywall didn't get sealed to the top of the top plate? Calculate every exterior wall 1 side and every interior wall both sides that cold attic air can travel down to those electrical boxes, switches and or out into the room at floor level.
Actually, I'm remodeling a particular room, and I am going to seal the drywall to the framing.
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Old 12-11-2019, 04:00 PM   #8
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Re: Air sealing around electrical boxes/outlets


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Originally Posted by jbrah View Post
Actually, I'm remodeling a particular room, and I am going to seal the drywall to the framing.
If you are not using a VB just caulk the holes in the outside of the box and exterior boxes have a perimeter gasket.

If the attic and floor is sealed properly there is no problem with interior walls.

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Old 12-11-2019, 04:07 PM   #9
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Re: Air sealing around electrical boxes/outlets


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If you are not using a VB just caulk the holes in the outside of the box and exterior boxes have a perimeter gasket.

If the attic and floor is sealed properly there is no problem with interior walls.

What's a VB?

My plan is to spray foam the knockouts on the back of the boxes (where the wires enter box). Once drywall is up, I was thinking I'd use spray foam to fill the small gap between the drywall and perimeter of box. Then outlet gasket under the cover plate.

How is that perimeter gasket installed? Seems if I were to put that around the box, then when I'm cutting out the drywall with a rotozip, the bit would chew up the gasket? I guess the gasket is thick enough that the bit doesn't go all the way through it, so you still get an air seal?
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Old 12-11-2019, 04:14 PM   #10
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Re: Air sealing around electrical boxes/outlets


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Originally Posted by jbrah View Post
What's a VB?

My plan is to spray foam the knockouts on the back of the boxes (where the wires enter box). Once drywall is up, I was thinking I'd use spray foam to fill the small gap between the drywall and perimeter of box. Then outlet gasket under the cover plate.

How is that perimeter gasket installed? Seems if I were to put that around the box, then when I'm cutting out the drywall with a rotozip, the bit would chew up the gasket? I guess the gasket is thick enough that the bit doesn't go all the way through it, so you still get an air seal?
Those boxes come like that the drywall sits against the gasket.

Watch the video here.

https://www.shdelectric.ca/archives/1240
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Old 12-11-2019, 06:37 PM   #11
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Re: Air sealing around electrical boxes/outlets


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Electrical boxes in a wall are similar to Belly Buttons, there's innies and outties. If cold air is coming into the room through the box it's originating from somewhere else. If air is going out of the box it's exiting somewhere else. Look at the big picture to stop the air flow. In my opinion, attempting to seal those boxes is similar to placing a Styrofoam cover on a hydrant on the side of the house to prevent freezing.
That hydrant you speak of is called a spiget
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Of course they had already been around for over 200 million years but on a planet that could go for billions of years maybe captain Kirk would have had big teeth and a long tail.
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Old 12-11-2019, 06:57 PM   #12
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Re: Air sealing around electrical boxes/outlets


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That hydrant you speak of is called a spiget
When someone determines how to spel it i'l use that word more.
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Old 12-11-2019, 07:20 PM   #13
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Re: Air sealing around electrical boxes/outlets


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When someone determines how to spel it i'l use that word more.
https://www.beedictionary.com/common...cket_vs_spigot
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Of course they had already been around for over 200 million years but on a planet that could go for billions of years maybe captain Kirk would have had big teeth and a long tail.
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Old 12-11-2019, 07:26 PM   #14
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Re: Air sealing around electrical boxes/outlets


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Originally Posted by Nealtw View Post
Those boxes come like that the drywall sits against the gasket.

Watch the video here.

https://www.shdelectric.ca/archives/1240
I get it, thanks. Wish I knew about these before I installed all the electrical boxes!
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Old 12-13-2019, 05:16 AM   #15
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Re: Air sealing around electrical boxes/outlets


First seeing boxes like those. Does that mean the outlets can be installed without the ground pigtail? What info I have is fairly old. I thought the inspectors wanted to see the ground wire out of the outlets?
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