Best approach to air sealing existing outlets?
Currently engaged in an energy efficiency upgrade. We have largely figured out most of the air barrier and sealed with a mix of membrane (Henry Blueskin), tapes+liquids (Tescon and Visconn), and even a little caulk and spray foam here and there.
That said, there are some areas where we can’t easily access the top plate and our early blower door test showed leakage through the outlets and switches on the walls with the unsealed top plate.
My current thinking is to try and seal those drywall penetrations, effectively making the top floor drywall on those faces the relevant air barrier.
What’s the best approach for air sealing existing outlets?
It seems the gaskets don’t do a great job. I can obviously easily apply caulk around the gap between the outlet and the drywall, but that still leaves the knockouts and wire penetrations unsealed.
Is there such a thing as an airtight outlet & cover?
Thanks in advance!
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I think you are going to have to air seal the boxes themselves. Though I will point out that, when you air seal just this wall, you still have communication with other walls in your house as the wires run between walls, so I don't think just air sealing at drywall on this wall is going to do anything. You will get air from all your other walls using this wall top plate penetrations. If you are really concerned with it you could always rip the drywall just below your top plate in a strip and air seal there. Idk if thats worth it but would probably be the easiest way if you can't access from above.
Yeah, we actually contemplated exactly this. I came out with the view that it isn't probably worth it to do all the drywall cuts...
I'm hoping for something like the airtight led recessed light replacements. As long as you can get a good seal around the light, they should theoretically be airtight.
Any idea on the air tightness of the tamper resistant outlets?
No sure about the tamper proof, I do think you could get a fairly good seal on the box from the inside using a tape like tescon vana and some origami skills. I found it to one of the better ways to air seal boxes. Foam I found just breaks when wires wiggle in the slightest and caulk and putty can be messy, especially on the inside I would be a little worried about it. The tape is low profile an tolerates wire movement.
Yes, they make airtight outlet boxes. There are a variety of brands, but vapor seal is one:
https://alliedmoulded.com/product/two-gang-electrical-box-for-use-with-nonmetallic-sheathed-cable-2302-nkv/
Another option is to apply putty pads, typically used for fireproofing, to the backside of the box after the wires are run.
Another option is these cardboard things that you then spray one part canned foam between the cardboard boxes and the J box.
If the space is finished you can seal the boxes with an extra long tip on a caulk tube.
That is not an outlet, it is a junction box
Thanks. Fixed. I was tired.
These are all great products. Unfortunately I'm trying to solve a different problem: that of an existing outlet already behind a wall...
I'd prefer not to open the walls to seal the backs of the outlets...
I guess the question is can I use firestop caulk (or putty) from the inside of the outlet?
If the space is finished, you can seal the locations in the boxes where the wires penetrate the box, and the random holes in the box with an extra long tip on a caulk tube.
Most of the air leakage is usually between the drywall and the box, so I'd start by removing the plates and sealing that gap.
can you put material inside of the box? sure.
is it a good idea? no
just guessing but NEC likely doesn't want anything foreign inside of the box.
the # of conductors allowed inside of a box is dictated by the quantity and size of the wire and number of devices. seems sketchy to estimate how much box fill volume would be diminished.
practically it's really hard to seal around wires or sheathing. conductors move when you stuff receptacles or switches back inside the box.
drywall layer isn't sealed at the floor either so stripping the drywall at the top means stripping the baseboard at the floor too.
Duct seal putty has been recommended in the past for exterior wall outlets. It is pretty malleable and can wrap around where the wires enter the box. Your situation is a lot tougher since drywall is already installed. Blower door directed air sealing should have happened while you still had access to everything.
Well, the house was built in 1930 and last remodeled in 1990. The walls in question weren't opened with this current project. We did do a mid-project blower door test and did see some air leakage through these outlets, hence my desire to seal them. As I understand it, putty on the inside of the box is a no-go right?
You typically don't want to use up any of the space in the box as there is a min amount of free space needed for wires & outlets, etc.
You also don't want anything flammable inside the box.
That is why caulking with an extra long nozzle works well if you really want to get into the back of the box where the wires come in.
Otherwise, just remove the plate covers and seal the gap between the box and the drywall. That helps ALOT.
I just got through sealing old boxes with this nozzle. https://www.amazon.com/dp/B005OLQJL4?ref=ppx_yo2ov_dt_b_fed_asin_title
Works pretty well, although to attach it to a caulk tube tip, I actually had to glue it on with heat glue. I fail to see how the plastic threads are supposed to even remotely grip or bite into a standard caulk tip, let alone hold on given the extra pressure require to push caulk through the long thin nozzle. Also, I recommend a high quality caulk gun, or your squeezing hand will be angry with you.
If you can meticulously put duct seal putty in the right spots in the back of the box, without adding significant volume, that's fine. Not flammable, not subtracting from the required space, not using a material that's not approved for the purpose. Opinions seem to vary as far as how long it will take to dry up and crack but it will never be worse than without it.
I like 3M FB-FOAM for sealing outlets. See https://www.amazon.com/3M-Block-FB-Foam-Orange-Aerosol/dp/B008KNP928/, although it's probably cheaper locally. It's less sticky and easier to shape than most spray foams, so it's easier not to make a mess.
Any way you do this you need to remove all devices from the box to get towards the holes in the back.
I got the best results from a caulk tip extension with Sashco Big Stretch. Make sure the caulk is fresh; much easier to push in when it is fresh. The challenge is making sure you push the sealant to it DOES NOT take up any space in the box - you don't want a blob in the box. You want the blob behind the box. With caulk you fill probably find you need to remove the wires from the devices, to separate the wires and get caulk between them. Then reattach the devices and stuff them back in the box before all the caulk cures. If one of them start to creat a gap when you stuff it, reseal at the gap and wait until the caulk cures before putting the box back in. If you put enough of it in there, it should work. It is tedious and messy and inevitably every few boxes you will find stuffing the device back in breaks the seal. You will get better at it as you go, prebending the wires as you apply the caulk. It is ALOT of effort.
The next best results were from Dap Latex canned foam, as it remains somewhat flexible when it cures. The effort vs result ration were worth the somewhat reduced air seal, but I also stopped removing wires from devices by this time. Wait until it cures, use a small screwdriver to trim away any excess foam that is taking up space in the box.
Then I got concerned about the Dap foam and started using the 3M Fire Block foam linked above by DCcontrarian. At that point I stopped looking for an alternate solution and if I had to do it again, I'd default to the 3M fireblock. Spray it in, shape it with the nozzle, remove what excess you can with the nozzle or another tool (I cut some scrap "sticks"), push the device and wires back in before the foam cures.