Radiator reflectors, do they work?

[TSS]

Has anybody had experience of using radiator reflectors (e.g. http://www.shopeco.co.uk/index.asp?function=DISPLA... ) to reduce heat loss from radiators on outside walls and could you feel any difference?

Thanks,

TSS

[neenaw]

Hmm, I'd be interested to hear what people think about these, I've been thinking about getting some for a while!

[robinhood21]

I have them on my outside facing radiators. Do they work? To be honest, I don't know. 'Tis not easy to reflect on whether they do what they say they are supposed to do on account of having no real way of checking the before and after usage of gas (new installation).

[Iain328]

Cardboard (or hardboard), PVA glue, ALuminium foil, Blue Peter moment (!)

Edited by Iain328 on Thursday 12th November 18:34

[grumbledoak]

I can't imagine they work that well, if at all. Household radiators don't really radiate that much heat- they are placed by windows to get a flow of cold air down through them to warm up...

[Ferg]

Hold your hand in front of a radiator at a distance of a couple of inches. A very small proportion of heat is actually 'radiated'. Those things hanging on your wall are 'convectors' really. The heat comes out the top, across the ceiling and down. Flat relective might help a bit, but I think those ones look like they might obstruct the air flow.

[Sam_68]

They don't do any harm, but they don't do much good, either.

As Grumbledoak says, radiators don't actually radiate heat; they transfer heat mainly by surface convection.

You'd be better off devising a casing for the radiator that increased the efficiency of convection airflow over them (perhaps using similar principles to a race car diffuser to speed up the convected air?).

They do prevent a little of the heat that the air has picked up from the radiators being transferred to the wall and thus lost through the building envelope, though.

[Simpo Two]

Iain328 said:

Cardboard (or hardboard), PVA glue, ALuminium foil, Blue Peter moment (!)

As indeed the young Simpo set to work doing just that in about 1980!

[dirkgently]

Sam_68 said:

You'd be better off devising a casing for the radiator that increased the efficiency of convection airflow over them (perhaps using similar principles to a race car diffuser to speed up the convected air?).

A shelf above a radiator increases its efficiency by 15% if i recall rightly.

[CO2000]

Simpo Two said:

Iain328 said:

Cardboard (or hardboard), PVA glue, ALuminium foil, Blue Peter moment (!)

As indeed the young Simpo set to work doing just that in about 1980!

I remember my Dad making up these in the mid 80's. In a similar vein he fitted rear seatbelts in the late 70's when most people didn't bother.

[zcacogp]

dirkgently said:

Sam_68 said:

You'd be better off devising a casing for the radiator that increased the efficiency of convection airflow over them (perhaps using similar principles to a race car diffuser to speed up the convected air?).

A shelf above a radiator increases its efficiency by 15% if i recall rightly.

Interesting ... can someone explain this to me - I'd never head of it before.


Oli.

[SJobson]

zcacogp said:

dirkgently said:

Sam_68 said:

You'd be better off devising a casing for the radiator that increased the efficiency of convection airflow over them (perhaps using similar principles to a race car diffuser to speed up the convected air?).

A shelf above a radiator increases its efficiency by 15% if i recall rightly.

Interesting ... can someone explain this to me - I'd never head of it before.


Oli.

And to me - how much gap is optimum, too, because resting a shelf directly on top of the radiator would block airflow and reduce the convective heating.

Replacing older radiators with modern ones with multiple fins is the best way of improving heating, for a given size. Convection is based on surface area and the fins massively increase the area.

[HiRich]

I can't comment on those particularly, but I disagree with those who have suggested they have minimal effect.

I have used the foil-coated foam (both cheapo stuff and the engine bay stuff) and it has quite a significant effect on wall temperature, 5-10 degrees I'd reckon. I've no idea what that means in energy/power terms, but it will add up to few kilowatts and it definitely had a positive effect on bills and warm-up time. Payback in a year or two. Three examples:

• Badly positioned radiator in bedroom with furniture in front, struggled to bring the room up to temperature. After fitting, warm-up times significantly improved.
• Main radiator (with sofa in front): Wall temperature behind radiator down c.10 degrees. It's notable how warm the back of the sofa gets some 6-12" away.
• Hallway radiator in a box cover. Not only foil backed, but I later added a curved section to duct air out the front at the top. Temperature of the top wooden surface dropped at least 5 degrees, and the radiator was wound down significantly whilst delivering the same performance.

For cost & effort, I recommend it. The only tip I can give is if the edges of the panels/foam will be visible, finish with aluminium tape. This gives a cleaner, straighter edge which is less likely to peel or be picked at.

[TSS]

Thanks for the replies everybody - quite mixed reports. I think I might get some reflectors for one radiator and then do some experimenting with an infra red thermometer.

[HiRich]

TSS said:

...and then do some experimenting with an infra red thermometer.

I like your style.

[Sam_68]

HiRich said:

I disagree with those who have suggested they have minimal effect.

...it has quite a significant effect on wall temperature, 5-10 degrees I'd reckon. I've no idea what that means in energy/power terms, but it will add up to few kilowatts.

It's a bit more complicated than that.

Sure, they reduce the local surface temperature of the wall immediately behind the radiator. But you then have to consider how much of that localised heat is actually lost to the outside air (through a couple of air gaps and another layer of highly efficient insulation material, in most modern cases), how much is spread though the 'thermal mass' of the relatively dense and conductive inner leaf of the building envelope (where it has the effect of reducing the rate of heat flow elsewhere, since the rate that heat is conducted through a solid element depends on the temperature drop across the element). It all gets pretty complicated, and is very dependent on the precise wall construction, but the net effect is that limited localised insulation of the wall behind the radiator doesn't have such a dramatic effect as you might expect.

I wouldn't disagree with your assessment of payback period, but then the relatively low cost of the measure means that a 2 year payback isn't anything to write home about... you're not going to be able to retire early on your savings. And - as usual with the payback periods promised by BunnyHugger technology - it fails to take account of the fact that you'd be better off just putting the money in a buidling society account and watching the compound interest accumulate.

[ShadownINja]

I suspect connecting black heat sinks to the radiator would have a useful effect as the heat would spread in the metal with more surface area to convect off IYSWIM. You can buy fins to hang on the back of radiators that don't have fins. I suppose you could do the same on the front but it would look a bit ugly.

[HiRich]

I don't disagree with the science, which I understand fully. But I'm convinced that energy saving was significant - £20 or more each year on already quite low levels (and when gas prices were a lot lower). Even then it's difficult to be precise with too many variables - how cold was it each year? was I in the house as much? what other insulation & draughtproofing did I put in?
I can only say with certainty that the installation in the hallway had a remarkable, instantaneous effect. Within a few days I'd noticed it was much warmer (too warm) and wound the radiator down significantly. Also noticeable was how much more quickly rooms warmed up (a comfort benefit rather than financial) as the heat went directly to the air, where you want it.

I can't prove it with numbers, but I was suitably impressed. For the small outlay, I have to say it's worth trying at least once.

[Ferg]

HiRich said:

..wound the radiator down significantly.

I don't understand what you mean by this.

[jeff m]

Any material that reflects heat from the wall and directs it back into the room will help.
You do not need a 90 degree wall.

If that heat is then deflected out into the middle of the room by something everyone seems to think is a shelf this will also help.

The alternative is, the hot air will rise up the wall to the ceiling.