Radiator reflective foil

[Moonraker]

Does it lose its effectiveness if emulsioned over? This one, though expensive looks ideal, any experience here please?

[Terry Fields]

Yes.

Shiny metal reflects infra-red (and other electromagnetic waves) because it's shiny and metallic.

Emulsion over it and you change the surface to one that isn't shiny and isn't metallic.

Metal reflectivity ~90 percent

Paint reflectivity ~10 - 20 percent.

A 50 micron layer of oil on a shiny metal surface increases the absorption from 10 - 20 percent to 80 percent.

Terry Fields

[Martin Brown]

It has to be a mirror surface to be "not a black body" at thermal wavelengths. Same way that thin metallic coating is used on survival blankets to get maximum reduction in heat loss for minimum weight.

The way it works to stop heat loss is by being a mirror surface reflector - and preferably backed with 3-5mm of expanded polystyrene to insulate it from the cold wall as well. Both play their part here.

stick it onto the radiator itself you reduce the convective heat output.

The best buy at the moment are the roughly 60cm square sheets for foil backed with 5mm of polystyrene in B&Q/Wickes. They mount onto the wall. See the previous thread for details.

Regards, Martin Brown

[fred]

In article , Moonraker writes

doubt given:

The only stuff like this that works is foil with a thin layer of insulation backing that is stuck to or otherwise fitted very close to the wall. It works by reflecting radiated heat and providing a little insulation where it is most needed. Painting it will remove any radiation reflecting benefit.

Attaching bare foil of any flavour directly to the radiator, as proposed on the linked site, is a total waste of time and is highly likely to reduce the heat output from the radiator.

Given the apparent misinformation presented on the linked site I would recommend avoiding it..

[NT]

No. Radiators convect, they dont radiate, and a shiny metal surface makes no difference to convection or conduction. Its a waste of kitchen foil.

NT

[Martin Brown]

I'll second that.

Regards, Martin Brown

[Ian Jackson]

In message , Moonraker writes

radiator. However, as this type is held in position with magnetic tape, presumably it goes on the metal of the radiator itself.

As its wall-side surface is shiny, this should reduce the radiator's radiation in the direction of the wall. As its radiator-side will also be shiny, this will reflect heat back into the radiator.

As presumably it won't be seen, why would you even want to emulsion over it?

As matter of principle, yes, anything which reduces the reflectivity of a radiating (or an absorbing surface) will reduce its effectiveness in radiating/absorbing heat. However, it could be argued that the thickness of the paint reduces the heat conduction to/from a metal surface of the paint.

[Martin Brown]

Actually it makes a fair bit of difference once the temperature of the radiator is above 50C or so. Convection is still dominant but you can also feel the thermal radiation in front of most decent radiators.

Reflecting that away from *outer* walls is worthwhile, but far better with insulation behind so the foil is thermally isolated.

I have seen someone get caught out by an old style linear regulator PSU they put in a basic folded shiny aluminium case and it got so hot that it went into thermal shutdown. After painting it black it was

[Moonraker]

Thanks for all the help, the general opinion is that the magnetic stuff a rip off but it is worth using reflective foil, so I will send my daughter to B&Q or Wickes for some, as it for her house!

[NT]

Yes, everything radiates, the question is how much. Radiators don't radiate to a significant extent, meaning the conducted heat output is very much greater. What's wanted to cut heat loss is insulation, not a reflector.

NT

[NT]

I think you'll find tesco and sainsburys far cheaper.

NT

[RobertL]

[dennis]

You have to be careful, just because its black doesn't mean it behaves as a black body.

[Doctor Drivel]

Yes.

[Martin Brown]

The difference is extremely marginal.

The visible light colour bears no relation to the thermal IR properties. Almost *any* colour of paint that is not mirror finish metallic radiates like a black body at the sort of thermal IR wavelengths characteristic of the Earths ambient temperature.

Tactically if you want to keep a building cool painting it brilliant white is the optimum. This was done of observatory domes until quite recently when modern aircon became preferred and the domes are now painted with a very sophisticated semi metallic off white paint system that has neutral heat loss properties under a clear night sky.

The old stuff used to radiate too well leading to cold air currents spilling over the edge of the dome slit and turbulence.

Regards, Martin Brown

[Terry Fields]

The PSU was also shiny on the *inside*, so reflected heat back to the components.

Painting the outside black radiated enough heat away from the shiny inside aluminium that had absorbed (instead of reflected) the heat from the components, plus the case was warming from internal convection, adding to the proportion of total heat that was radiated and convected away.

Terry Fields

[PeterC]

a good adhesive and time to dry.

[fred]

redundant.

I'm not sure that that one has an insulated backing which in my view is the only one worth using.

Strong wallpaper paste perhaps with a dob of pva sounds good.

[PeterC]

Yes, sorry - Dialog has an anti-wrap feature so I tend to be lazy and use that.

It has a thin layer of PE(?) foam on the back.

TS does a strong adhesive that I used. The foil is still on after about 18 months.

[fred]

Poor wording by me I'm afraid, just meant to point out how toolstation links _can_ be shortened if you chose to rather than you _should_ have.

Excellent, I had considered recommending it to the o/p first time round but it wasn't clear on the TS description or photo (TS's main weakness IMV).