Might aluminum foil work for this?

Factual Questions
1

Whenever I use the over-the-sink light in my kitchen, the floor of the cabinet above it gets pretty warm. Not so hot that it can’t be touched, but warm enough that I sometimes wonder about the foodstuff in there. I have an idea to line the bottom of the cabinet with aluminum foil, as a kind of heat shield, but I also have two seemingly contradictory pieces of knowledge in my head: 1) aluminum foil can be used to prevent the edges of food from burning when used in the oven, and 2) metal conducts heat. I’m not trying to burn anything (like the cabinet) in the process of finding out whether the foil might work, so my question to those who know more about such things is:

Is it possible for a layer of aluminum foil to work as a heat shield in the situation described above?

2

A different solution would depend on what kind of tinkering you’re comfortable with. If you remove the ballast (the transformer) from the light’s casing and mount it off to the side or somewhere like that, it would also remove the heat source from the food-storage cabinet.

I can’t speak for the insulating effects of aluminum foil, though.

3

You won’t get much insulation out of a sheet of aluminum foil. However, aluminum is an excellent heat conductor, so if you affix it firmly to the wood, it should reduce your hotspot by moving the heat to other, cooler, parts of the cabinet floor.

4

Well, I’m no engineer, but I think that any benefits you’d see from simply putting down a layer of aluminum foil would be offset by the cost of that same foil.

What you’re dealing with here isn’t just heat transfer, but heat buildup. Aluminum foil can sheild, somewhat, against the heat, but once there’s enough of it there, you’re gonna feel it anyway. This is why you can cook something that’s wrapped in aluminum foil; it’s not some miracle insulation, it’s just metal.

So, while the aluminum may prevent/absorb/dissipate some of the heat, you’ve STILL got this hot light heating up the whole cabinet, and that’s gonna start to build up.

The best solution, I think, would be to do as jayjay said… try to remove the heat source. You may want someone knowledgable to do this, as electricity can be quite dangerous. But MOST of the heat from a flourescent light comes from the ballast (heavy metal thingy inside) and not the bulb, so you could potentially move that and keep the light where you need it. The remaining heat from the bulb will pretty much dissipate in a relatively well-ventilated housing, so your cabinets would be fine.

Alternately, you may try insulating the area between the light and the cabinet. I’d suggest removing the light, putting a piece of insulation on the bottom of the cabinet, then mounting the light to that. You’re still going to get a heated cabinet, but the insulation will reduce the heat flow somewhat, and maybe it will stay cool enough to protect your food.

Of course, if you’ve got a heat source underneath a closed container, anything in that container is going to be subject to heat. If this stuff is food, that’s probably not a good thing, unless the food is preserved or otherwise heat-resistant.

So, third option: Use that cabinet for something else. Either non-foods, maybe use that area for storing plates or glasses or something, or non-perishables. Dry goods like cereals and crackers and stuff usually withstand heat pretty well; fresh wet foods like fruits and vegetables are rather vulnerable to heat. Select foods that you could leave in the trunk of your car for a month, and keep those in there.

Fourth, and least reasonable, solution: Air Conditioning. Get a tiny little AC unit installed in your cabinet to keep your food cool. Crank it up enough, and you got an extra fridge! q;}

5

Misnomer:

I assume that the fluorescent in question is a 48" single tube ‘strip line’ fixture, i.e. it is in a white metal box about 2" deep by 3 to 3 1/2" wide and a bit over 48" long.

First choice would be to mount the fixtue on 1" stand offs to create an air gap beween the fixture and the bottom shelf of the cabinet. This eliminates conduction and the air gap allows air circulation to help cool the fixture and the ballast.
Very simple and economical.

Second choice would be to have an electrician or a qualified handy man mount the ballast in a metal box located away from the fixture where the heat would not affect stored items. Proper code wiring practice is to be used for such a relocation.

6

I don’t think the OP ever said anything about the light being fluorescent. So I’ll add that if it’s not fluorescent, you may want to try a lower wattage bulb. Other then that, I second the idea of just putting something else in the cabinet.

7

I’m a scientist and much of my work these days relates to heat transfer. I’m pretty sure several of the previous posts went off on wrong tangents.

Aluminum’s a great conductor of heat but that isn’t going to matter much here. The path along the plane of the foil is way too long and narrow to conduct much heat that way. The foil will conduct heat through its thickness, but no more heat than you’ve already got there.

First of all, if the light is an incandescent bulb, and it illuminates the bottom of the cabinet, it’s doing quite alot of radiative heating. The aluminum foil wil redirect most of that elsewhere.

Second of all, multiple layers of aluminum foil, if there’s a bit of air separating them (such as if you lightly crinkle each layer first, and then only partly smooth out the crinkles), can be a fairly good insulator. Even though the aluminum is a good conductor, at each aluminum to air interface some of the heat becomes infrared radiation, and at each air to aluminum interface the infrared becomes heat. These transitions don’t work well for shiny metals. It’s great to block infrared radiation because it travels so well whereas the part of the heat that is just conducted has a hard time making it through the air.

Third, it will take a while (maybe something like an hour) for this whole system to stabilize once you’ve turned the light on. After that, there won’t be any more buildup of heat. The heat will be leaking through and out of the cabinet as fast as the lamp is supplying it. Someone posted an analogy of food in an oven, and it’s not the same thing. Food in an oven has noplace else to send the heat it gets, and has to wind up at oven temperature eventually, whereas the cabinet can pass heat off in all directions.

It is dicey to tell someone over the internet that their perceived problem is not dangerous and they don’t need an electrician to avoid a fire. But if the hot spots are not charred yet and you just want a bigger margin of safety, yes, foil can act as a heat shield here. Try changing a hot light bulb with and without some foil to grab it with - you’ll see it’s somewhat better with the foil.

Now, then - you could also improve things with a heavier piece of aluminum in there. Can you fit a shallow baking tray into the spot? Or some sheet metal, say something you can buy at a good hardware store? Can you move the lamp further from the surface? If it is incandescent, can you replace it with one of those newer fluorescent type bulbs that wastes less energy as heat?

8

Wow, some good info/suggestions here…thanks, everyone!

Joey P is correct: the light above my sink is not flourescent, it is two incandescent bulbs. I didn’t mention that in the OP because my question is the same no matter the heat source. Also, the light is not mounted to the cabinet in any way: it is mounted to the wall between the cabinet and the sink.

I’m not trying to keep the stuff in the cabinet above the light from boiling or anything; it doesn’t get that hot. Just warm enough for me to think I might not want to put food up there. I’ve lived in this house for over a year, and have been careful not to leave that light on for too long – it might reach some sort of ‘critical mass’ of heat, or it might just keep getting hotter, but I’d rather not experiment. :eek: Currently I don’t keep anything perishable in there (a couple oven mitts, cooling racks, some kitchen towels, etc.), and it sounds like that’s what I’ll keep doing.

Replacing the light fixture or doing any rewiring is out, as the house is a rental (and I’m not DIY inclined). I will look into lowering the wattage of the lightbulbs, but I don’t want to sacrifice too much of the light output – there’s a reason a light is installed there. :slight_smile:

If I understand Napier’s post correctly, it doesn’t sound like it will hurt to try lining the cabinet floor with sheets of aluminum foil, so I might just give it a go and see what happens.

Thanks again!

9

Crap, I hate to post twice in a row, but I just thought of a follow-on question (inspired by Phnord Prephect’s suggestion of insulating the space between the light and the cabinet): do you think it would make any difference if I layered aluminum foil underneath the cabinet above the light, instead of layering the foil on the inside floor of the cabinet? If I were to combine that with a lower-wattage bulb, would the reflective foil help offset the low wattage?

(Also, after seeing these replies, thank you for your patience with my scientific ignorance. :slight_smile: )

10

Ah. My mistake. I thought you were talking about fluorescents.

But in that vein, why don’t you try some of the fluorescent bulbs that are designed to be screwed into incandescent fixtures? They’re much cooler than the equivalent wattage of incandescent bulbs and they’re cheaper to run as well.

11

That is a much better idea. Napier’s comments about radiative heat are correct. To benefit from his ideas, you need to have the foil between the cabinet and the light source, **not ** in the cabinet. As a bonus, it can only benefit your lighting arrangements.

12

Take a look at the option mentioned by Napier of switching to a mini-fluorescent bulb that screws into a regular socket. You can replace a 60-watt incandescent bulb by a 12-14 watt fluorescent one that produces the same amount of light, but runs much cooler.

I did this with my over-sink light in the kitchen, and I leave it on nearly all the time, with no heat problems. And saving electricity, too.

These bulbs cost quite a bit more, but they commonly last several years. Remember to put the old bulb in and take this one with you when you move out of there!

13

Napier raises several good points.

Oh, wait, I’m Napier… how embarrassing…

But I wanted to point out that the aluminum foil should be on the bottom surface facing the light bulbs, not on the upper surface of the wood. Someone else points out foil would work better on the bottom - but note it is actually a little DANGEROUS to put the foil on the top of the wood. Here’s why:

No doubt the wood presently reaches a certain equilibrium temperature and gets no hotter, because it loses as much heat to the interior of the cabinet as the light bulbs give it below. But if you insulate the top of the wood, it will have to equilibrate at a higher temperature to export the same amount of heat upward through the new insulation. You certainly want the aluminum foil on the bottom (that is, if it’s overheating the wood that you should be worrying about), which instead will lower the temperature of the wood to export a now smaller amount of heat upward.

It also makes a difference what kind of bulb you have. Fluorescents put out about a quarter or a third of their energy as visible light and most of the rest as conducting or convecting heat. Incandescent bulbs put out as little as about 1/50 of their energy as visible light, and a bigger share of the rest is converted to thermal infrared, most of which the foil will reflect. So the radiant heat issue is bigger with incandescents. The glass envelope is the infrared radiator in this case (it’s opaque to the infrared inside, or at least that longer than about a micrometer or two in wavelength). If it’s a halogen bulb, this is even more true - halogen bulbs work with a much higher envelope temperature that allows tungsten to leave the envelope and go back to the filament where it belongs, helped by the chlorine or bromine or whatever halogen they use.