reflective barrier behind radiators ?

kevin_5 · May 2003

> To perform. Just putting foil directly behind 
> the rock and applying the rock in direct contact 
> with the foil won't gain you anything but a vapor 
> barrier. Metal is a great heat conductor when in 
> contact with an object. From my mechanical 
> engineering books,I believe a 3/4 inch air space 
> is optimum. 
> 
> Boilerpro 
 

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George_8 · May 2003

reflective barrier behind radiators ?

hello,I'm doing a remodeling project and we are replacing the wall board.I was wondering if it would be benificial to install reflective foil under the sheetrock behind the iron radiators to deflect radiant heat back into room?
George

ed wallace · May 2003

reflective barrier

better to put a sheet metal reflector behind behind the radiator i have done this with sucess

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kevin_5 · May 2003

HI George, Ed is probobly correct that it would be more effective to put a metal reflector directly behind the radiator, but while you have the rock off I would go ahead and put a bit of the reflective foil behind it anyway.

You are bound to get SOME benefit even if you don't do anything more than that. I reason thus because my radiant ceiling panel has heat emission plates on top of it which I believe are part conductive/part reflective in operation and the sheetrock ceiling is a pretty good emitter.

Anyway, It's not going to cost you much to put it in, and you may wish you had someday if you don't.

Actually I believe there is a benefit to putting the radiant barrier around the entire house either on the inside walls or as a housewrap. Some would disagree with me, but many agree.

Just think why they mirror the glass in your thermos bottle. Not even a vacuum can stop radiant heat transfer. The sun and outer space prove this too. KEVIN

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kevin_5 · May 2003

do the foil

HI George, Ed is probobly correct that it would be more effective to put a metal reflector directly behind the radiator, but while you have the rock off I would go ahead and put a bit of the reflective foil behind it anyway.

You are bound to get SOME benefit even if you don't do anything more than that. I reason thus because my radiant ceiling panel has heat emission plates on top of it which I believe are part conductive/part reflective in operation and the sheetrock ceiling is a pretty good emitter.

Anyway, It's not going to cost you much to put it in, and you may wish you had someday if you don't.

Actually I believe there is a benefit to putting the radiant barrier around the entire house either on the inside walls or as a housewrap. Some would disagree with me, but many agree.

Just think why they mirror the glass in your thermos bottle. Not even a vacuum can stop radiant heat transfer. The sun and outer space prove this too. KEVIN

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Steve Ebels · May 2003

Just talked with

One of the guys from Low-E insulation this morning. My problem was with a radiant floor home that needed more heat than the floor could supply. He said they have had excellent results with wrapping houses with their 1/4" reflective foam insulation. The insulation carries an r-value of 4. Similar result were observed when the insulation was applied to interior walls also. I'd do the whole exterior wall if it was my house. I've had nothing but positive results with this stuff.

Boilerpro_3 · May 2003

Reflective barriers must have an air space

To perform. Just putting foil directly behind the rock and applying the rock in direct contact with the foil won't gain you anything but a vapor barrier. Metal is a great heat conductor when in contact with an object. From my mechanical engineering books,I believe a 3/4 inch air space is optimum.

Boilerpro

kevin_5 · May 2003

Air space

I think I know where you're going boiler pro, but what about the air space between the rock and the radiator, and what about the air space in the insulation between the foil and the outside wall? It's not the same application as a staple-up. If we study this thing, I think we'll see some benefit. If I'm thinking crooked please explain.
Kevin

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Boilerpro_3 · May 2003

Same idea as staple up

If using Foil faced insulation, the insulation provides the air space on one side, but you have to provide one on the other. In a wall where you are trying to refect radiant heat in (as in Northern climates) if that foil touches the rock it becomes a conductor and transfers the heat from the rock to the insulation. If you look at installation instructions for foil faced products, they will talk about these requirements. I have seen particularly clear info on this when looking at foil faced insulation board. They show two r-values in the charts one with an air space and one without. With an air space, you pick up about 2.5 points in R-value, depending on the temp difference between the two surfaces. Those plastic/foil faced products have air bubbles in them to provide this air space. Take a close look at all the specs on these products.... it is quite eye opening.

Boilerpro

kevin_5 · May 2003

Here I go again

Wow, what a quick response! OK I agree with you that you definitely get MORE benefit if you have an air gap. All I am saying is that even with the foil between the rock and fiberglass insulation you still get SOME. Now you mentioned the bubble wrap that some use to provide the "air gap". Doesn't the dead air in the 4" of fiberglass do the same thing? And if the foil conducts all the benefit away to the fiberglass, doesn't it conduct it all away into the bubble wrap as well? Bear with me, but I'm thinking you get the radiant reflective benefit regardless of how an incorrect installation may royally foul up the conductive side of things. Once again, you could get more or less reflective benefit dependent upon installation. In any case, in the context of the first post above he could install some of the foil/foam or foil/ bubble wrap with tabs stapled between the wall studs, cover it with rock and get SOME benefit, Yes or No ?Kevin

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Tom_10 · May 2003

Just completed

my own house using cast iron sun rads (hot water monoflo). Used the method you described of a sticky back foil insulation I picked up at the Depot. While I had the rock down I foiled, re-rocked, and foiled over the rock and stapled it for good measure. Then put in the rad against the foil. The heat is intense when it comes up. Sized all rads to the appropriate loads/room. It works beautifully. The foil has an r value of 6 too. A bonus in my eyes. But using your line of thinking, I figured it couldn't hurt to double up (or could it). I'm not sure I'd notice the difference if I hadn't. It really does reflect a generous amount of heat. Plus, its not a whole lot of $$$ extra to double up so why not?

Tom_10 · May 2003

Is that to say..

3/4" clearance between the foil insulation and the back of the radiator for max. effectiveness?

kevin_5 · May 2003

The way that I understand it, part of the "r6" that they claim is due to the radiant reflecting capability, and so it won't matter how many sheets you stack together, you are only getting benefit from the top one. However if it is bubble wrap or foam behind the foil, these are providing some amount of conductive heat resistance, and I suppose the more the merrier. Of course they also stop convection (air movement) but aren't designed for that as they don't seal tightly at the edges. That is what blown in or fiberglass is for. Some would argue just how accurate the factory "R6" claim is , however, there is definitely something to the radiant benefit. Kevin

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Boilerpro_3 · May 2003

No,.....

that 3/4 inch space is a "dead" air space (no air movement), which isn't what you get around most radiators due to convection currents.

Boilerpro

Boilerpro_3 · May 2003

A not so quick reponse

If the foil is in continuous contact with the rock, no benefit can be expected. It is the reflective qualities of the outermost layer that matters, just like the paint on a radiator... only the outer layer effects heat transfer. The 4 inches of fiberglass will do the same thing (lots of little air spaces), but only for radiant heat reflected on that side. In northern climates the foil usually faces in, so the insulation is on the other side. With the foil bubble wrap, the refective foil can face the air space in the middle, so you still get an air gap even if it is installed in direct contact. When installing faced insulation between studs, the wings are supposed to be stapled to the sides of the studs, not the faces. Installed this way, you will get an air gap, and get the benefit. However, most faced insulation I've seen is installed with wings stapled to the face, so there is no air space. Bubble wrap includes it own air space, so its harder to screw up.

Boilerpro

reflective barrier behind radiators ?

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