Airtight metal electrical boxes?
Alexander_Riccio
| Posted in Energy Efficiency and Durability on
When not in NYC, or otherwise using Romex and plastic boxes, I can use AirFoil boxes to get a clean airtight box, or can do some ugly stuff with Big Stretch to seal all the wire penetrations.
I find it’s a lot harder to safely caulk a metal box – especially since I’m usually dealing with AC cable, so the bare metal is my primary grounding conductor. Between the pre drilled holes, the knockouts, and the cord grip, it’s hard to get an air and pest proof seal on these boxes….
Is there a type of metal box that is easy to make airtight, like the airfoil?
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Replies
Alexander,
All I've seen used are plastic box covers. See post #18 in the comments:
https://www.greenbuildingadvisor.com/article/airtight-electrical-boxes
The easiest way is probably to use a "putty pad", such as this:
https://www.amazon.com/Rectorseal-66340-6-Inch-7-Inch-Metacaulk/dp/B008A3UA04/ref=sr_1_2_sspa?crid=1XNERVAXEPGQX&dib=eyJ2IjoiMSJ9.KL3nrI4n85_S_ymDI-IJQMaBREMunPqesve96zgDEz3pJBAqHnHiTMtxSdzdqZjv4i7q7Bdr8lch5LAv6lqKNI1-dKEbrEn1ziF3gokLulkrbOubVpiCVgQKIq0mnDWp8HIVwGvNobWGx7k7cO6pMpa2EVUndF02RuByl7SXeLTId9ywY8ENFnH_GtmAS_2jjXSu09zOo2RBWmk8EX6xReYM8-RDgCpaAco2AqUulyWxhhCYu6xRhocy2IpgwZKSWzXs7w_X0cMQyITrnXj8979sktiuRY24bKKN_sKEGFU.5V-c8E1nZCQvqo9Nngx_ODTGfLlw9ZI8M84NN9OrVi8&dib_tag=se&keywords=fire+putty+pad&qid=1734142664&sprefix=fire+putty+pa%2Caps%2C129&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1
You can mold those to the box, they're a sort of sticky clay-like material. They're easy to use, but not particularly cheap if you have to seal a lot of boxes. The other option would be to use "bell boxes", although those are usually used for outdoor applications, so I'm not sure how well they'd work in a wall. At least with those, you can use thread sealant on the threaded connectors and the box itself is diecast and should be air tight.
If you didn't need to use AC/MC cable, then I'd use the white fiberglass "hardboxes", which are also air tight aside from the knockout you punch out to bring in a cable. I have found some of those boxes now have the screw holes for the device going all the way through, so I give the back side of the holes a dab of canned foam or caulk to seal those. These boxes are far better than the usual plastic boxes in many ways, air sealing is just one way they're superior.
Bill
For my house I used zip tape to seal the unused knockouts and caulked around the wires going into the box.