The breaker box is located in the laundry room of the house, which itself is an air conditioned space. I bought the house in the summer and this winter the room has been extremely cold even when the rest of the rooms in the house are warm. Upon investigating I noticed that cold air was flowing into the laundry room from around the breaker box, so I took the front panel off the breaker box to reveal the following:

whole breaker box

Air primarily seems to be entering from the bottom right hand corner where the main electric cable from outside enters the breaker box. However, when the panel cover was on, I could feel cold air coming through the holes in the boards both to the left of the breaker box (all the way up and down the length of the box even though they are on the other side of the stud cavity that the breaker box is located in), and below the breaker box (where the insulation is).

Here is a closeup of what I believe are the problem areas (based on where I could feel cold air coming in):

close up of breaker box

pulling away the insulation reveals that the air enters the area below the cavity because there are holes to let wires through, and air then enters the stud cavity to the left because there are holes in the stud to let wires through.

In addition, there is an opening to the outside where other cables enter the house which can be more clearly in the picture below.

opening to outside

My questions are:

  1. What is the best and safest (because I am working around electricity) way to plug up the main hole (the one in the bottom right of the breaker box where the main electric cable enters the box?

  2. What is the best and safest way to plug the other holes (at the bottom of the breaker box, in the left stud, and in the foam board)?

2 Answers 2


What you are looking for is duct seal. You can pick it up at most home centers. This will seal the external conduit, where the power line enters the house.

For sealing the studs, you could get a can of insulating foam (Great Stuff or another brand). The Firestop type would be your best bet.

Any place wires penetrate your siding, you should seal them with an outdoor/weatherproof caulk.

I wouldn't recommend sticking anything into the breakouts on the box itself. If you want to, you can get some better sealing bushings for these, but you'll have to pull the wires and reconnect them. Sealing the outside conduit will give you the best bang for your buck.

You should also investigate the outside. It looks like the wired are coming straight in from the back, rather than through a mast. If there are any other boxes on the back (like your meter) you should caulk around the outside where the box meets the siding.

  • I put the duct seal in the bottom right of the breaker box where the main cable comes in from outside, correct? When doing so, do I need to turn off the main breaker to avoid being electrocuted? Commented Dec 20, 2015 at 2:35
  • Yeah, wherever the cables enter. If its a conduit thats best, but if its just cables (which is code violation i believe) you can still seal them directly. These cables are always hot, as they feed the breaker. You should be safe, but rubber boots and gloves never hurt.
    – ench
    Commented Dec 20, 2015 at 5:43

I had a similar problem. Thanks to ench's answer, I bought some duct seal opened the right angle cap and gasket (on the external part of the house) and stuffed the duct seal in the entrance hole. This seems to have sealed off the draft.

I considered putting the putty in the electrical box but I was weary of potential accidental electrical contact, resulting in personal bodily harm. (aka not worth it)

I also used duct seal around the pipe entry areas to further seal other drafts, and since I was already there.. I did all the external entry ways (old phone line, cable, ect) the same way.



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