Radiator foil.

[Zebra]

This may be a bit of a silly question. You know that radiator foil that you can stick to the wall behind your radiators to reflect heat back into the room? Well, if you were planning on having column type radiators instead of panel type radiators, and therefore the wall behind could be seen, would the foil be effective if it were buried in the wall? For example the rear external living room wall I've yet to insulate and plaster (lime/sand mix over woodfibre insulation boards) so could perhaps bury some foil behind the insulation boards. Any point?

 

[MdB]

Nope. Sorry.

Foil works by reflecting radiated light/heat that falls on it. This requires a layer(*) of air (or something else transparent in the infrared). If there is something solid touching it - like plasterboard, lime etc - then there is no radiation happening and heat transfer works by conduction. Foil is very good in the heat conduction stakes so it is of no benefit.

The foil is also non breathable...

(*)I'm not sure how big a layer of air is required. I seem to remember reading somewhere that a couple of cm is needed but I don't see why a few microns shouldn't be enough from a physics point of view. There is probably something I'm missing though I really ought to know about this sort of stuff considering I have optics consultant on my business card...

 

[Zebra]

Aha, jolly good, thanks MdB, I shan't do that then. I could get one but not fix it, and just slide it down the back when it's chilly..... In the summer it could be stored with the thermal underwear, hot water bottles, fluffy slippers, hats and gloves....

 

[worms]

I have optics consultant on my business card...

Is an optic not the measuring glass on a whisky bottle behind the bar?

 

[88v8]

In our previous house - a phrase of which you may be wearying, sorry - I installed column rads throughout. In three rooms I insulated behind the rads by sticking cork tiles to the wall and making a decorative frame around them. Eeurgh, you may think, and in this photo it does look a bit that way, but without the flash, it was invisible. The rads were on the same wall as the windows, and I made sure it was invisible by appropriate room lighting.
In t'other two rooms, no pic, sorry, the rads nestled under a window sill and, again, the lighting ensured that the eye was not offended.

And the remaining rooms in the house? Beacuse of window/rad positioning, the cloak of invisibility would have been moth-eaten, so no cork. For me, form trumps function, every time.

Ivor

PS incidentally, the oak plinth beneath the rad provides a means of fitting carpet without having to unplumb the rad. For preference I would always fit wall-hanging rads, as they obviate this problem and also permit of wall-papering without the rad being unplumbed, but 30+ years ago there were no new iron rads, and it wasn't so easy to find the right used rads in the right sizes in the right output.

PPS the rad valves are Crane (D200 & D201), still in production.
http://www.cranefs.com/files/productDataSheets/D202_203_Data-sheet.pdf

 

[Zebra]

Ah, so you've used an alternative method, cork, which although not reflective, is an insulator. Would this be equally effective? In which case, if I am insulating my walls internally with woodfibre boards, then I don't need foil anyway. Belt and braces perhaps.
I actually don't think the cork looks bad Ivor, what with the shelf and surround. I like your radiators too.

 

[worms]

My physics is rusty, but I would think the foil helps to radiate the heat, while the cork ensures that more of the heat is convected. (I suppose on most panel radiators, the foil on the wall actually radiates the heat back to the radiator itself and increases the amount convected).

 

[MdB]

Heat within the radiator will be released to the environment via conduction and radiation. Convection will cause the air heated by conduction to be moved around the room.

Foil will cause most of the radiation which lands on it to be reflected back into the room instead of being absorbed by the wall. On the other hand, it is a good conductor so heat transferred to it directly by conduction (little) or indirectly by convection (most) will be absorbed well and transferred to the wall.

Cork on the other hand will absorb most of the radiation which lands on it but being a fairly good insulator will reduce the amount of heat absorbed by conduction / convection.

Foil over cork will have the benefits of both and is hence the reason why Celotex/Kingspan typically comes with a foil layer.

 

[MdB]

... considering I have optics consultant on my business card...

Mrs MdB has pointed out that I don't have "Optics Consultant" on my business card. I have instead "Optics Consulant" . I really must get some more made.