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Old 12-30-13, 05:24 PM   #11
Nonhog
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Funny I was just thinking about this subject. I was thinking a box made out of rigid insulation around the plywood box that keep the insulation from creeping up to the light. My question would be how tall would the air space need to be? Maybe a section of ducting about a foot tall would work?

Those bags are looking pretty good right now!

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Old 12-30-13, 05:28 PM   #12
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I put a few conventional (air leaking) cans in my house several years ago. To stop the air flow I boxed them in with framing lumber and capped them with the biggest disposable turkey roasting pans I could find. The inverted pans rise above the insulation so I suppose there might be some convective action when the attic is cold and the lights are off. I don't notice any cold spots around the cans though.

The enclosed area is large enough to dissipate the heat. The aluminum pans don't get hot to the touch even with 150 watt floods. I sealed the pans with silicone caulk. It was cheap and works like a charm.

CFL's or LED's would eliminate the problem, but there is no guarantee someone won't put another 150 watt bulb up there. And until LED floods come down in price and prove their durability I intend to continue using conventional floods.
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Old 12-30-13, 05:39 PM   #13
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Quote:
Originally Posted by doug30293 View Post
the biggest disposable turkey roasting pans I could find.
Those turkey pans are looking pretty good right now.
What if you add 2 pans per canned light. One one upside down, One on top of that right side up. Then roll (key would be rolled insulation) up and over both? Hmmmm have to play around with that idea.

If these ideas are in conflict with OP. I'd be glad to edit. Let me know.

Last edited by Daox; 12-31-13 at 04:34 PM..
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Old 12-30-13, 08:30 PM   #14
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Quote:
Originally Posted by doug30293 View Post
I put a few conventional (air leaking) cans in my house several years ago. To stop the air flow I boxed them in with framing lumber and capped them with the biggest disposable turkey roasting pans I could find. The inverted pans rise above the insulation so I suppose there might be some convective action when the attic is cold and the lights are off. I don't notice any cold spots around the cans though.
One problem with using your suggestion might be that a reflective surface like a roasting pan will insulate from radiant heat, but it isn't really an insulator. In other words, it will keep the heat in but it won't keep the cold out. At night in winter with the lights off and no insulation on top of the pans it will be a clear channel for cold to be transmitted into the house. Can't be avoided. You've sealed off any air leakage, which is good, but you've effectively removed insulation where each pot light resides.

So you're back to the problem of trying to get maximum insulation above a pot light that sits proud on the attic side of the ceiling drywall. There's only so many work-arounds, some better than others.
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Old 12-30-13, 09:27 PM   #15
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The workaround would obviously be lower wattage bulbs and full insulation. The proper fix is TC rated cans to prevent a fire hazard if too large a bulb is inadvertently installed.

The flood lamps are in this case a specific preference - or indulgence. They are rarely used. I swapped out the two 150W floods in the shop a few weeks ago, one CFL and one LED. I'm going back to floods until my stock runs out.

The drywall around the can (light off) in my office is the same temperature as the rest of the ceiling with a 20F temp difference between inside and outside. At dT=40F last week the difference was still negligible with no motion in the convection indicators (cobwebs in the can).

If I lived up north where dT=50 is normal I probably would rethink this fix. Here in Georgia it's all about infiltration, and palmetto bugs that crawl through holes in the attic.

The weather is supposed to drop back into the 20's this week. If time permits I will do some heat loss evaluation and report back.

Doug
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Old 12-31-13, 09:36 AM   #16
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Quote:
Originally Posted by doug30293 View Post
If I lived up north where dT=50 is normal I probably would rethink this fix. Here in Georgia it's all about infiltration, and palmetto bugs that crawl through holes in the attic.

Doug
Doug is being polite in referring to "palmetto bugs". You others know the damn things as COCKROACHES! Living up north, I never knew how big these suckers could be until I moved south. Most of 'em you see walking in with a suitcase . . .

But back to cans, heat and insulation. Can you still buy a 150 watt incandescent flood? I think the caulked in turkey pan over a can fixture is a great idea especially if covered with insulation. Cheap, good infiltration barrier and easy to put in. This is now on my list!

Thanks!

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Old 12-31-13, 03:17 PM   #17
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Yep, any bug you can hear walking around at night is too big to be a house guest.

I bought a dozen 150W floods in 1994 to have on hand for a large contract job I was doing. The client supplied all our lights so I came home with a full case. Floods feel good when working under them in a cold shop.

I probably could cover the pans with insulation since the can enclosure is at least 2 cubic feet. I doubt the temp rise would be significant even if 100W was escaping upward.

Tomorrow morning I will check around the cans with an IR gun before the sun comes up. Right now the temp around the cans is the same as the rest of the ceiling. Inside air is 63F, outside it's 42F.

There is actually more temp drop (2F) where the ceiling meets the walls at the header plate. The corresponding area of the soffit outside shows a 2F rise. Makes me wish I had paid more attention to this before the soffit went up. The headers need foam but I'm not crawling over there again.
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Old 12-31-13, 03:33 PM   #18
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I was so happy rattling on that I forgot to answer your question. McMaster Carr still sells 300W incandescent and 80W halogen floods.

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