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Air sealing metal electrical boxes

I'm looking for a good way to air seal metal electrical boxes. Local code requires conduit for all electrical, and no plastic boxes.

All of the solutions I've found are for romex and plastic boxes. I know there must be something for conduit and metal boxes.


Asked by James Lenihan
Posted Jul 7, 2014 5:30 PM ET


4 Answers

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As far as I know, LESSCO boxes accommodate metal electrical boxes. Here are some links:



Answered by Martin Holladay
Posted Jul 7, 2014 5:53 PM ET


I use "putty pads". They are code compliant fire blocks and air-sealing, pliable putty sheets that fit and stick to odd and difficult shapes and angles. They also serve to dampen sound transmission through walls which is particularly bad at electrical boxes. Get them warm before applying.


You can see them in use on Google image.

Lesco boxes are not possible to air seal. No reasonable methods of applying caulking materials can be used to seal the wire penetrations.

Answered by flitch plate
Posted Jul 10, 2014 1:57 AM ET


You wrote, "Lesco boxes are not possible to air seal." The method recommended by the manufacturer -- sealing the wiring penetration with 3M contractors' tape -- works, and has been verified by blower-door testing.

Answered by Martin Holladay
Posted Jul 10, 2014 6:13 AM ET


Martin .. I have tried both and here is why I landed on putty pads:

1. 3M tape and pretty well all contractor tapes oxidize; and so may become brittle and fail with time and wear. They make me nervous so I would prefer to use the higher end tapes.

2. Putty pads are code compliant for fire stopping; and I like that a lot for sealing electrical boxes and adjoing wiring for obvious reasons. Putty pads are intumescent while tape is not.

3. Lesco boxes create a wasted cavity/space around the electrical box that should be insulated on the outside wall and used for sound proofing when between interior walls. Electrical boxes and dead air spaces are high in the transmission of sound through the wall compared to other wall elements. Putty pads are dense and way better at sound dampening.

4. I have used both and I prefer the workability and installation ease of a warm putty pad; whereas tape is hard to wrap through and around a wire where it protrudes from a box and next to other wires and features and narrow spaces.

But putty pads are more expensive and both methods are time consuming. Frankly, I woud not trust a contractors' crew to do the Lesco boxes or putty pads properly. These air sealing, sound proofing and fire stopping details are labors of love. Definitely check eash installation.


Answered by flitch plate
Posted Jul 10, 2014 11:45 AM ET

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