Insulation in Gang Box

I have a deep 3 gang box on and exterior wall. There is cold air that pours out of it since I am guessing not much insulation could be put behind it. Is it safe to fill the gang box with fiberglass insulation?
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I don't know the regulations, but my gut feeling says it wouldn't be safe to fill the box with insulation. Instead, I would remove the outlets/switches, and break away a few tabs on the back of the box, then spray minimally expanding foam behind the box. After it has finished expanding, cut or break away any insulation that is in the box, and caulk around the openings and where cables enter the box. I'd also caulk around the outside of the box where it meets the sheetrock/wall covering. Reinstall devices, put on the cover plate, and you should be good to go.
Anthony
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HerHusband wrote:

And then place a foam gasket under the cover. This won't block all of the air, but it will block most of it. I don't know of a safety issue with regard to fiberglass insulation inside the box, but it likely won't be very effective and will really annoy the next electrician who works on that outlet.
Matt
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No, you need free air circulation. Insulation would violate code, and (properly) be a hazard. Plus, were I an electrican and I found loose fiberglass in a box, I'd charge double to take it out!
Get some squirt foam in a can, and squirt that behind the box (not inside! Nothing but wires in a box, please...) Tha may help. Also gasket the cover plate which may help some as well. 'Caulk' between the box and the sheetrock (or plaster) as well if possible.
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The best solution that no one seems to have addressed, it why is there air movement in the outside wall cavity? Check at the header and sill plates and find out why there is air infiltrating the space. Fix the problem, not the symptom.
s

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Brian wrote:

Fiberglass insulation will do nothing to stop air infiltration and it is useless as long as air is leaking through or around it. The best solution is to find where the air is leaking into the wall cavity and seal it there. If you can get above and/or below the wall to where the electrical goes through the header and sill plates and shoot some expanding foam in all the holes the electrician created it will probably solve your problem.
If you can't do that then use a switch plate gasket. Stopping the air from exiting the wall cavity should also stop the air from entering it. That will allow any insulation that is in the cavity to do it's job.
--
Art

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Never put anything inside an electrical box except for approved components. Foam and fiberglass are not approved components.
Lets get the myth that fiberglass will STOP air flow. It can only do this if jammed extremely tight into a confined space. When it is this tight its insulation value is worthless. The insulation value of a product is dependent on how many and how well air pockets are trapped. In the case of installing fiberglass tight enough to STOP air flow the amount of air space is greatly reduced and the amount of glass is greatly increased. Glass is great are transferring heat.
I agree with the answer to turn off the power to the outlet, remove the outlet/switch (should not need to unwire). Use non or low expanding foam behind and beside the box. Let set and trim any foam that ends up in the box. Use a good grade of caulking to seal all holes in the box and around the wires. Hint (tape about 4 inches of a straw to the end of the caulking tube to reach the back). Let caulking and foam setup good before reinserting outlet/switch (this could take several days).
If done properly the air leakage should be near zero, this would mean the foam gasket will do little or no good for air flow. It will add a small amount of insulation to a very weak area so put it on anyway.
As for the answer "Fix the problem, not the symptom". Good luck, if one looks at how a house is put together and the endless gaps between the studs and plates, 2 by's and drywall, holes drilled by plumbers, HVAC technicians, cable, phone and electricians etc. Not that I disagree in sealing plates, most of the top plate can be sealed providing one wants to move all the insulation in their attic over every interior and exterior wall (yes it is recommended). Use caulking or expanding foam, if the gap has a heat producing device such as recessed lights (non IC, non air tight) do not seal. If it is a fireplace, vent for furnace or water heater the can normally be sealed with metal and fire rated caulk and or fire rated foam (check with local codes).
Then there is the leaks of the siding, yes it is supposed to leak air. The drain plane is next, it can leak air (should not leak water). After the drain plane there may or may not be sheathing and if one has ever looked at it installed it has lots of gaps.
So if the house was built correctly in the first place we would not be hiving this dialog.... But then I'd be out of business.
Remember to do the inside wall outlets and switches as most homes have interior wall that a technically out side (yes that is correct).
I hope this helps
Qualifications: Studying residential energy since 1981 Performed over 7,500 residential energy analysis Presently doing Whole House Performance diagnostics. We use Building Science to diagnose houses
Andy
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The most common place that the air is coming from is almost always oversized holes drilled for the wiring to pass through. This is usually in the attic and usually difficult to find. The suggestion for using foam is the best idea, just remove any that enters the box (under special circumstances it has been known to change into an extreme fire hazard).

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