air sealing electrical boxes…from the inside or outside?
BrunoF
| Posted in General Questions on
For better air-sealing I have gone with surface mounted flush lights as opposed to recess cans but still need to seal the junction boxes in the ceiling. I am at rough in stage right now and can access all sides of the box easily. Should I put sealant / putty inside the boxes or apply those products from the outside?
Thanks.
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Replies
The easiest way to air seal a box when you can access the back is probably going to be a to use a fire putty pad like this: https://www.amazon.com/Rectorseal-66340-6-Inch-7-Inch-Metacaulk/dp/B008A3UA04/ref=sr_1_2_sspa?crid=15ZZTEYZLVMZD&keywords=putty+pad&qid=1700488497&sprefix=putty+pad%2Caps%2C98&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1
That stuff is a conformable, sticky, clay-like material, so you can form it around the back side of the box and adhere it to the box and the mounting surface (drywally, etc.). It makes an excellent air seal for the entire box this way -- you can even seal around wires with this stuff. The only real downside is you have to access to the back of the box to be able to apply the material effectively.
Bill
Whenever possible air seal the boxes from the outside. Anything applied to the inside takes up space in the box and the number of wires allowed in a box is governed by the number of cubic inches inside each box. If you reduce the space inside the box, you could make it a code violation.
I caulked most of my boxes to the drywall and wires it did not take very long. I applied some of the extra “Great Stuff” leftover from the windows to a few
Walta
Second the fire putty. $5 a pad. I just did it (to only 5 boxes), but I could tell not only does it air seal, it's going to actually be a fire stop unlike foam. Not that there is going to be a fire...but why not?
I agree this is probably the best method.
I would say it is a very expensive approach, especially when you’re doing a whole house. They do make fire block spray foam.
Thx folks