Recessed light sealing ideas

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Got a question for the residential guys. I've got 4 recessed lights that I would like to seal up air tight as part of a larger sealing/insulation project on a 1950s vintage home. I'm trying to get the whole ceiling plane as air tight as possible before insulating, & can lights are not helping that.

I think these are IC-rated fixtures (will verify first), and I've already replaced 120W bulbs with LED snap-in downlights at like 20W. Also patched plaster gaps around penetrations.

I see a couple ways to go: Could foil tape & otherwise seal the existing fixtures airtight & insulate over them. Easier, but won't be full depth insulation over fixtures. Also would be a problem if someone sticks a 120W bulb back in there. Or could remove whole fixture and install a regular metal j-box like all the other lights, plaster patch around that. More work of course.

Anybody got any slick ways they retro these? Also, what products do you like for air sealing box penetrations?

Thanks
 

Stebs

Member
Location
E. Ks
Build a box around them, seal it, and insulate over top of it?

Might also google "recessed light insulation box"
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
The energy codes normally require "air tight" housings. You can find many residential cans that are listed as air tight, or listed as complying with the energy code.

If I remember correctly, these still need to be sealed against the drywall with a gasket (like electric-light mentioned) or with caulk.
 

JFletcher

Senior Member
Location
Williamsburg, VA
You want an IC rated airtight old work can, like this. Foam gasket on the trim will help too, as will replacing the insulation on top of it.

100+W bulbs will cause the thermal trip to cut out.
 
JFletcher and steve66: That old work can is a good tip and thanks. I guess that's the way a guy needs to go to get airtight while dealing with the possibility someone sticks a high watt bulb back in.

I think if I go to the trouble of removing and replacing it though I'll try to eliminate the can projection in the attic altogether though. Maybe replace with a flush mount/puck light type setup and regular ceiling box.

Does anyone do any caulk/firestop/mastic/whatever sealing on all the holes and penetrations in a regular 4-O box? They are pretty porous.
 

JFletcher

Senior Member
Location
Williamsburg, VA
JFletcher and steve66: That old work can is a good tip and thanks. I guess that's the way a guy needs to go to get airtight while dealing with the possibility someone sticks a high watt bulb back in.

I think if I go to the trouble of removing and replacing it though I'll try to eliminate the can projection in the attic altogether though. Maybe replace with a flush mount/puck light type setup and regular ceiling box.

Does anyone do any caulk/firestop/mastic/whatever sealing on all the holes and penetrations in a regular 4-O box? They are pretty porous.

I see you are in WA state. The cans linked above comply with your state's energy codes. The only time I have sealed 4 square (1900) steel boxes is in rated walls, in hotels, where there are over 100" of opening or less than 24" horizontal spacing. In all but one case, moldable putty pads were installed by us or the firestop contractor. They are draft, smoke, fire and sound seals.

Overlamping cans with a medium base bulb is physically possible of course, tho I do not know of any recessed can lights with that socket that do not have a thermal overload built into them - I believe it is a requirement for listing:

http://iaeimagazine.org/magazine/2001/07/16/thermal-protection-in-recessed-luminaires/

'Ghost switching' or can lights coming on and off by themselves is a sure fire indicator it's overlamped and the cutout is doing its job. I replaced hundreds of these at a hotel I used to work for; previous maintenance got a 'great deal' on those 25000hr 100W bulbs, and installed them everywhere. If not for those cutouts I'm sure there would have been a few fires, tho several severely overloaded dimmers were found melted and on their way.
 

MNSparky

Senior Member
Location
Minneapolis, MN
Occupation
Electrical Contractor - 2023 NEC
I've had builders contruct foam boxes to go over the top of cans that get sealed to the topside of the sheetrock. This is usually done because the cans are not IC rated, but they've done it to create an airtight seal as well.

I've also used the tin tape that HVAC installers use to seal up holes in boxes. It works great and isn't effected by heat like putty or duct tape.
 

Electric-Light

Senior Member
I've had builders contruct foam boxes to go over the top of cans that get sealed to the topside of the sheetrock. This is usually done because the cans are not IC rated, but they've done it to create an airtight seal as well.

I've also used the tin tape that HVAC installers use to seal up holes in boxes. It works great and isn't effected by heat like putty or duct tape.

If it gets too hot, the foam might burn. Homes change tenancy/ownerships
 

MNSparky

Senior Member
Location
Minneapolis, MN
Occupation
Electrical Contractor - 2023 NEC
If it gets too hot, the foam might burn. Homes change tenancy/ownerships

The boxes aren't constructed to fit the can tightly. They are typically built to allow at least 3" clearance from the can. Heat will build up in there, but the thermal overload should trip long before the foam combusts. Besides, most cans I've installed in residential applications have max watts listed on them, typically around 65-75w, depending on the type of lamp. Never seen a 120w bulb in a resi can. 100w type A incandescent will usually trip the overload within 10 minutes, depending on the type of trim used.
 

Electric-Light

Senior Member
The boxes aren't constructed to fit the can tightly. They are typically built to allow at least 3" clearance from the can. Heat will build up in there, but the thermal overload should trip long before the foam combusts. Besides, most cans I've installed in residential applications have max watts listed on them, typically around 65-75w, depending on the type of lamp. Never seen a 120w bulb in a resi can. 100w type A incandescent will usually trip the overload within 10 minutes, depending on the type of trim used.

Why not just use an LED trim made for this purpose? It should say "AIR-TIGHT" on the box and comes with a foam gasket goes behind the flange that presses up against the ceiling sheet rock. I would not suggest using something that is not designed for this purpose, especially if it interfaces air handling space. The pressure difference will draw air through the LED chamber if the top and bottom halves aren't hermetically sealed and dust will accumulate inside the LED chamber or above the diffuser lens which is likely not removable.
 

MNSparky

Senior Member
Location
Minneapolis, MN
Occupation
Electrical Contractor - 2023 NEC
Why not just use an LED trim made for this purpose? It should say "AIR-TIGHT" on the box and comes with a foam gasket goes behind the flange that presses up against the ceiling sheet rock. I would not suggest using something that is not designed for this purpose, especially if it interfaces air handling space. The pressure difference will draw air through the LED chamber if the top and bottom halves aren't hermetically sealed and dust will accumulate inside the LED chamber or above the diffuser lens which is likely not removable.

The OP said he wants to make the lid as airtight as possible. Those LED trims do come with gaskets and some do claim to be airtight, but I'd put money down that they are not actually air-tight. The springs don't hold the flange to the ceiling all that tight and if the ceiling has any type of texture to it, there will be air leakage between the flange and the sheetrock. If he really wants to seal the cans up, he will have to get the can itself to be sealed or put a sealed enclosure over the can.
 
Why not just use an LED trim made for this purpose? It should say "AIR-TIGHT" on the box and comes with a foam gasket goes behind the flange that presses up against the ceiling sheet rock. I would not suggest using something that is not designed for this purpose, especially if it interfaces air handling space. The pressure difference will draw air through the LED chamber if the top and bottom halves aren't hermetically sealed and dust will accumulate inside the LED chamber or above the diffuser lens which is likely not removable.

Like MNSparky says I haven't seen a trim yet that's truly air tight. The ceiling is textured and the springs don't hold very tight at all. I have some of those now and they are decent, but not air-tight.

Since I will be the only user on this, think I will foil tape and seal the existing fixture or replace with 4-O boxes and puck lights.

And thanks JFletcher for the tip on the putty pads, think those will be just the trick and need something to plug all the other wiring holes and such anyway.
 

Electric-Light

Senior Member
The OP said he wants to make the lid as airtight as possible. Those LED trims do come with gaskets and some do claim to be airtight, but I'd put money down that they are not actually air-tight. The springs don't hold the flange to the ceiling all that tight and if the ceiling has any type of texture to it, there will be air leakage between the flange and the sheetrock. If he really wants to seal the cans up, he will have to get the can itself to be sealed or put a sealed enclosure over the can.


"Certified airtight per ASTM E283-04" but you could use silicone or gasket sealer of some sort if you really wanted it tighter. It would leave residues on the sheet rock but only under the flange where it's out of the view. Remember that interior sheet rock itself is not vapor tight and the surface area is large enough that it's far from hermetically sealed. That's why vapor barriers are used on exterior wall
 

JFletcher

Senior Member
Location
Williamsburg, VA

MNSparky

Senior Member
Location
Minneapolis, MN
Occupation
Electrical Contractor - 2023 NEC
"Certified airtight per ASTM E283-04" but you could use silicone or gasket sealer of some sort if you really wanted it tighter. It would leave residues on the sheet rock but only under the flange where it's out of the view. Remember that interior sheet rock itself is not vapor tight and the surface area is large enough that it's far from hermetically sealed. That's why vapor barriers are used on exterior wall

Yes, you could do that. I certainly wouldn't want to be the guy to try to pull one down to service the can or lamp/trim. I foresee damage to the texture or, worse yet, the paper face tearing coming down with the trim.

I've had painters silicone my trims up before. They get this face when they do --->:rant:
 

Electric-Light

Senior Member
Yes, you could do that. I certainly wouldn't want to be the guy to try to pull one down to service the can or lamp/trim. I foresee damage to the texture or, worse yet, the paper face tearing coming down with the trim.

I've had painters silicone my trims up before. They get this face when they do --->:rant:

I wouldn't obsess too much over it. What they're worried about more is a large surface area that is open from having 3/8" gap around every fixture box and plumbing connection because of a sloppy builder and they're not expecting a submarine tight seal.

You don't use a ton and you don't do it like you caulk around plumbing fixtures. Use a tiny bead, like 1/16" width and the minimum necessary near the center so it doesn't squeeze out. Just enough to fill the tiny gap between the gasket and the sheet rock texturing and only when you need to such as when the sheet rock is warped enough to prevent seal from forming. You're not using it as a mechanically fastening glue.
 
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