Radiator Reflectors

barebain

I'm new to the wall, although I've been to this site before for advice, so I knew that this would be good resource for my question.



I've not been able to find any posts about this on the forum, but does anybody have experience or thoughts about the value of placing reflective panels behind steam radiators?  The theory is that without them, the radiator is merely heating the wall assembly, but if a reflector is used, that heat raditing to the back of the unit would be reflected in to the room.



I learned of this method reading about the recent Empire State Building energy efficiency rehab in which they are, among many other things, placing these reflectors behind the radiators in the building.  I'm not sure what they are using in this case, but I have seen online examples using reflective bubble wrap glued to luan, reflective rigid insulation, and even aluminum foil on cardboard.



Does anybody have experience with these techniques?  Do they work with a noticeable comfort difference, or are the effects nominal to non-existant?



Thanks.

jpf321

there have been at least

in recent months, there have been at least 2 discussions on this same subject. the answer seemed to be that YES it may well be beneficial to place reflective "panels" behind rads .. I think one person even suggested wrapping a large enough piece of cardboard in aluminum foil as the cheapest method .. if you dig around in past posts, you should find the two threads. 

gerry gill

I don't know how well the insulation

would work but i think anything would be better than nothing. Here are some pictures that may help your decision making.

Polycarp

radiant barriers

I don't know about real-world examples, but conceptually it should work. 



The reflectors in the Empire State building are effectively radiant barriers.  The most common application for these are in roofs.  Those emergency "space blankets" work on the same principle.  Basically, you take a material with very low emissivity (like aluminum) in the heat wave-lengths and combine it with an air space.  The lower the emissivity of the material, the more it will retard radiant heat transfer.  The key is that there must be a surface with high emissivity that faces air or it won't work.  Most materials with high emissivity for heat are also reflective, but there are some that aren't.



A radiant barrier will only help with radiant heat transfer.  The wall is still going to get warm, and you are still going to have conductive losses.  Adding insulation to a radiant barrier (like that foil-faced insulation at the supply house) will address both issues.  (Although, it's not a lot of insulation, so it won't do a whole lot for conductive losses.)



The foil-faced cardboard is a good low-tech way to do it.  The foil creates a good radiant barrier.  If the cardboard is the corrugated kind, the air gaps in the corrugation will help with the conductive losses.



I've thought that your could just construct some handsome frames with sheets of foil-faced rigid insulation in them and put them behind your radiators.  Giving some depth in the frames might cut down on the sight of the foil.  The ideal would be to integrate a radiant barrier into the wall behind all radiators.

Polycarp

reflectors

Gerry,



Did you take these pictures?  If you have access to a thermal camera, it would be great to see the impact of some reflectors.  I for one would love to see the impact of the low-tech cardboard with tinfoil approach and the foil-faced rigid insulation approach.  It'd take some time since you'd have to wait for the temperature of the materials to normalize, but I think it would show a lot.

gerry gill

Yup, i took those pictures,

at a house  i was doing a bathroom remodel at. It would be nice to do an experiment with different materials but if you look at just his radiator picture, he doesn't have hardly any room behind it for anything..ive a steam customer that put some kind of foam board behind his and he swears it works..i can't remember which type of foam board tho.

Polycarp

thin

Foil on cardboard would only take up about 1/4".  Then there is the stuff that looks like foil on bubble-wrap.  That's only about 1/4" as well.  The foil-faced rigid insulation would take up a lot more room.  I think the thinnest I've seen is 1".

Ex Maine Doug

I used foil bubble wrap

In my bank building in Maine I put the foil covered bubble stuff behind the panel rads and in the MD house behind the steam radiators.  Nothing fancy to try it, just cut the panels from a roll.  The walls behind the rads were always hot. Now they are cool. I tried it on one half of a rad for a couple of days and this convinced me to do them all.  The walls in ME are three bricks thick with plaster interior finish. The house in MD is a Craftsmen four square style wood structure with plaster interior walls and NO insulation (yet).



Maybe I will get to make nice wood framed panels some day for that stylish modern look. And maybe I will grow hair on my head.

David Nadle

Reflectors

You just need to put a reflective surface against the wall. I made a set for my house by laminating aluminized mylar to Eucaboard panels. A bit more durable than foil on cardboard, but not much prettier (I have radiator covers so you can't see them). They just lean against the wall and are easy to remove and clean.



I don't think you'll detect any comfort difference. At best the reflectors will take the 20% or so of radiator output that is radiating in the wrong direction and send a lot of it back into the room. Would you detect a comfort difference between a 800W heater and a 1000W heater? I doubt it. But reducing heat loss through the exterior wall will save energy in the long run.