Reflective Foil Insulation behind radiators

jambajoose

I have seen people put foil behind radiators. Does this help with conserving heat by reflectiving radiative heat back out into the room? Is this pretty marginal? I imagine it mostly doesnt help with insulating.

If it is helpful, I am also thinking about wrapping my steam pipes with this foil.

Kickstand55

I suppose reflective insulation can't hurt. Let us know if there's a difference.
As far as steam pipe insulation, best to go with fiberglass tubes with white covering. Some Big Box stores have it. Be sure to cover the fittings as well, it does make a difference.

jesmed1

I had some extra 1/2" rigid foam board foil-faced insulation, so I stuck some behind all the cast-iron radiators in our 100-yr-old house, but I can't say I noticed any difference. The best thing you can do to keep heat inside an old house is (1) air sealing of windows, doors, basement sills, and attics, and (2) insulating the attic and walls. Air sealing is easier to do and less expensive than insulating, so it's best to start there.

jumper

I used to back snow against walls of long driveway. Later I put aluminum behind radiators. Snow still melted first where radiators are.

Sylvain

Dan's talking:
https://www.heatinghelp.com/systems-help-center/do-radiator-reflectors-work/

SteamingatMohawk

If you do anything, be aware of reducing the air space between the radiator and the insulation, which could affect the vertical air flow.

It might be better to use the foil faced bubble insulation readily available at the Orange store.

24 in. x 10 ft. Double Reflective Insulation Radiant Barrier

I don't know how much difference it made, but it can't hurt and the price is minimal...a lot less than the blue store.

Jamie Hall

jumper said:

I used to back snow against walls of long driveway. Later I put aluminum behind radiators. Snow still melted first where radiators are.

Hay bales against the foundation. Used to do that all the time in Vermont...

LRCCBJ

Jamie Hall said:

jumper said:

I used to back snow against walls of long driveway. Later I put aluminum behind radiators. Snow still melted first where radiators are.

Hay bales against the foundation. Used to do that all the time in Vermont...

Were you ever able to measure the air temperature right at the foundation wall (behind the hay bale) and determine if it was higher than ambient?

Teemok

With all respect to Dan, my understanding of why you cover a turkey is very different.
The hot air flow path for most older fan-less ovens is from the bottom and out to the sides then up to the lid. The lid (hottest zone) is much hotter than the bird. That is, if things go well. The bird is always colder than anything in the oven. The whole time it's in there. Lid and sides are radiant panels aimed at the bird. The foil is so you don't burn/dry out the skin before the inside of the turkey is cooked. It reflects radiant away from the bird. Most chefs will pull the foil off for some amount of time after they have measured an internal bird temperature approaching done. Thus crisping the skin.

Respecting radiant reflection: It requires a clean shiny surface with an air gap for max reflective effect. You can't have anything in contact with it's reflective surface . You can cover it but you must leave an air gap. Studies prove that even dirty reflective surfaces still reflect a substantial amount of radiant heat. Is it worth it? That is a harder question to answer.

jesmed1

I'm pretty sure this is the only forum where you can get expert advice on troubleshooting a steam boiler AND cooking a turkey without burning the skin.

PGB1

Sorry- User Error

ChrisJ

After seeing some of the foil / insulation behind radiators on here I can safely say I'll never do it.

Yes saving energy is nice but cosmetics do matter as well and any small savings that may provide will never make the cosmetics worth it.

Some of them look down right ridiculous.

PGB1

I am a firm believer in radiant barrier after having been taught by the former chairman of ASTM's Radiant Energy Committee (and reading many published articles by NASA, Cal Tech & others).

We have it in our attics, some wall, a crawl space, behind some fin tube in radiation, behind a radiator and on some pipes. Ice dams are no longer a problem. The room above the crawl is finally warm. The air conditioner no longer runs non-stop.

There are keys to success:
1- Use pure, un-coated aluminum. There are many fakes out there. Many of the bubble stuff products don't work due to a coating. Some foil-foam boards are real and some are fake. Attic Foil Com is a legitimate supplier of many radiant barrier materials. There are other good suppliers, too. (And some that sell no good over-alloyed stuff.)

2- Leave A Gap of 19mm or more on one side or both!! It does not matter which side because aluminum is a 97% reflector and a 3% emitter. The Gap Is Critical. (That's why some foil-foam boards fail. People don't leave the gap.)

On the pipes where I have it over mass insulation, one can feel the temperature difference from about an inch away. Touching will show no difference because aluminum is a good conductor. (Think heat sink in electronics) I put some behind some fin tube in radiation and the snow no longer melts when it piles up on the porch against the bricks.

Our heating and cooling invoices show a large difference. I even went so far as to calculate using heating degree days.

Try This:
Ask a supplier for a sample. Place a cardboard box upside down and shove a stem thermometer through a wall. Cover the top of the box with the sample. Shine a hot light on the box from a few inches away. After 5 or so minutes, record the temperature. Remove the aluminum and watch the thermometer rise (fast).
Try it again with kitchen foil. The difference with and without isn't so much.

People argue radiant barrier and I've been told I'm crazy, but I have seen the proof at home, at work and at others' homes and buildings.

Paul
PS: Gold is a ca. 99% reflector/1% emitter. Silver is ca. 98%/2%. My bank account voted for aluminum at 19 cents US per square foot.
PPS: If you're laying it over mass insulation, buy the perforated so moisture isn't trapped.

Sylvain

One can wrap oneself in an emergency/survival foil blanket as an experiment.
Between 1 and 7 $

ChrisJ

@PGB1

I'm not sure anyone would argue that they work.
Look at any heat shield on an exhaust system of a car or catalytic converter, without them really bad things happen rather fast. It's just a reflector. I had to make one for the muffler on the generator I built to keep it from cooking the alternator. In my case I used 304 stainless.

Raw aluminum would seem like it would oxidize rather quickly though, so I'm unsure why that's so important vs other IR reflective materials?



But, as far as how effective the thing is, or how much it matters I am sure temperature plays a roll.
A 212F radiator isn't going to produce as much IR as a 1500F catalytic converter.

PGB1

ChrisJ said:

After seeing some of the foil / insulation behind radiators on here I can safely say I'll never do it.

Yes saving energy is nice but cosmetics do matter as well and any small savings that may provide will never make the cosmetics worth it.

Some of them look down right ridiculous.

During remodeling, I put perforated radiant barrier across the face of the studs, then 3/4' furring strips on the studs for the 19 mm gap, then the wall surface. On walls that got new mass insulation, I stapled the perforated barrier on the back of the sheathing, then furred the studs 3/4", then insulation. Then wall. It works great for our radiators (and whole house). So, if you're ever remodeling...

On the baseboard units, It's carpet taped to the inside back wall of the enclosure so that there is a gap to the emitter (fins). Invisible.