Radiator reflectors

[ss]

Is it worth putting the aluminium refelecting material behind a radiator, is it cost effective or more to the point does it save money.

[Davey]

I have just done it, so cannot confirm, but it seems sensible, and doesn't cost much. Wickes sell it online. I remember reading somewhere that an IR scan of the outside of houses will show where the radiators are, so any mitigation of heat loss must be good.

[polygonum]

A few years ago my mother had this done as part of an energy saving scheme for older people. Bizarrely they managed to put it behind all the radiators on internal walls - including the bathroom one which backs onto the airing cupboard. Which seemed a complete waste of time and money.

[ss]

I agree I was thinking only on outside walls.

[gremlin_95]

We have a few rolls of this which we've not used yet, only got it on one radiator. Simply haven't got round to doing it!

[PeterC]

I did it the summer before last as the rads were off anyway. Got the (slightly) insulated type from Toolstation and used a strong adhesive. Mine was on to emulsion, so there's virtually no absorbtion into the wall or foil which means that it takes a long time to dry. No figures as I don't monitor the useage that closely.

[NT]

better to use insulation than baking foil, though you can use both. ISTR rough calcs indicating the return wasnt great.

NT

[Kostas Kavoussanakis]

The ones I have seen claim that their shape causes better air circulation:

Kostas

[Andy Burns]

the words "green" and "shop" in the URL, I was on a downer before I even saw them.

At £39 each, two or three required per radiator, how many rads on outside walls in an "average" house? four or five ... I'd like to see the payback period for over £400 of shiny foil.

[Roger Chapman]

>>> With the words "green" and "shop" in the URL, I was on a downer before I

It looks as though the £39 is for a pack of 20 so the cost is nowhere near £400 but still good little money earner for what appears to be metallised plastic.

Am I alone in thinking the explanation from the website which I have pasted below is a bit short of real science.

"In a room with a typical central heating setup, much of the warmth is lost into the walls behind and above the radiator. The remaining heat gathers at ceiling level where further losses into the fabric of the building can occur. With inefficent heat distribution your room will be prone to cold spots away from the radiator, that seem to take forever to heat.

The metallised Heatkeeper Radiator Panels have been engineered with a clever saw-tooth design, that causes warm air to spin outwards back into your room instead. This reduces the time it takes to heat those chilly rooms and the wider spread of heat virtually eliminates any cold spots, making your radiators much more efficient.

The heat that was once lost into the wall is reflected back into the radiator, so that the water circulating inside travels back to your boiler hotter. A boiler full of hotter water"

The way I see it if these things are really reflectors then the amount of hot air being mysteriously spun is neither here nor there. Only that which is not reflected back can warm the reflector and a small part of that will be returned as radiation anyway.

To maintain temperature equilibrium all of the introduced heat has to be lost somewhere but it seems to me that the heat loss is by no means as concentrated as the blurb implies. Only the bit of wall directly behind the radiator gets radiation directly from the radiator and it is common practice to install radiators directly below windows in an attempt to even out temperature variation in a room.

The heat radiated back to the radiator would make the radiator warmer than it otherwise would be but that would in turn mean that the radiator would give out more heat as well as have a higher return temperature. That in turn would cause the room thermostat to cut the boiler off slightly sooner to avoid overheating the room. The only saving would come from the extent to which heat loss from the room had been reduced.

The way I see it putting reflecting foil behind a radiator will reduce the heat loss through the wall behind the radiator but won't have much if any other effect on the room. Given that the area of wall hidden by a radiator is small any savings are going to be small. As has been mentioned on this ng recently 'radiator is a bit of a misnomer these days. Radiators with fins convect more than they radiate and the hot air rising from the fins of a single panel radiator is going to have much less effect on the wall than the radiation.

[Andy Burns]

Heh, I did think it sounded like a right rip-off :-)

I couldn't see how the little fins would produce such a vortex to force large amounts of the hot air to circulate downwards, per this diagram

[NT]

Sawtooths can create eddies. This will slow the overall upward airspeed, worsening the evenness of heating in the room.

NT

[Roger Chapman]

answer is clearly 'magic'.

I didn't get as far as those diagrams which seem absolute nonsense. You are going to get hot air convecting up both sides of the radiator regardless of what is on the wall behind the radiator. Even if you have a cold draft falling down the wall it isn't likely to displace the convected air to anything like the extent shown. Convection currents off radiators are gentle which means they rise fairly directly. You need a fan heater on full wack to blast hot air horizontally for the sort of distance shown.

[Owain]

Does this mean that my condensing boiler will be operating at less efficiency?

Owain

[dennis]

They probably can't.. however a radiator shelf is a well known way to "push" the air back into the room.

[Roger Chapman]

Only if you leave the pump and/or the boiler controls alone but of course you are already optimising your boiler performance by driving the return temperature as low as you can get it so the answer to your question is actually no.

[Martin Brown]

It is worth doing for any radiators that are on outside walls. No point in heating up the bricks on the *outside* of your home. A thermal IR scan image of a house will show hotspots where there are radiators on outside walls. You want the slightly thicker semi rigid square sheet sheet rather than the thinner roll material provide you have the space.

Radiators on internal walls don't really need doing since the heat going into the wall comes out in an adjacent room. ALthough it might marginally speed up warming a room from cold I doubt it saves monet.

Closing the curtains where radiators are underneath windows is even more important to prevent loss of warm air to no advantage.

Regards, Martin Brown