Do insulated radiator panels save money? - I'm testing them now

tobykim

I've seen this stuff on a roll in B&Q and wondered if it's effective, we live in an end of terrace which is stone built and the outside wall gets very cold, we have 2 radiators on the gable wall so I wondered if this would be any good to us, also how did you fix it to the wall?

mattymoo

tobykim wrote: »

I've seen this stuff on a roll in B&Q and wondered if it's effective, we live in an end of terrace which is stone built and the outside wall gets very cold, we have 2 radiators on the gable wall so I wondered if this would be any good to us, also how did you fix it to the wall?

We got the B+Q rolls a couple of weeks ago. They suggest using an R4 adhesive but I have absolutely no idea what this is. Even Google wasn't much use.
In the end we used double sided tape. Cut the panel to size, make slits from the bottom to accomodate the radiator wall brackets. We then put tape accross top, bottom and sides and peeled back an inch or so of top layer.

We then drop the panel (the tape has given it some rigidity) down the back of the rad and peel off the tape. Much easier to do if you have already peeled back part of it.

To early to tell about energy savings but I have dropped the room thermostat a couple of degrees at the same time and not felt any noticeable difference.

We do have a rad in a utility room which has a polycarbonate roof. This room gets very cold in winter and the only way to warm up used to be by standing against the rad. With the foil behind, I can stand 12" away (30cm) and still feel a strong heat.

tobykim

Thanks for that I'm just going to put them on the rads that are on the outside walls so was curious as to how to fit them thanks again

kernel_panic

They do.

The full answer is complex, though. The theoretical heat loss reduction achieved by using reflective materials was pointed and worked out at least 30 years ago (1). The basis for the potential energy savings lie in the fact that a radiator transfers energy to the surroundings in two ways: convection and radiation. The energy transfered through the latter amounts up to a quarter of the total for a double radiator, and double that for a single one (2). When a reflective surface is fit on the wall behind the radiator, the temperature of that part of the wall will be lower and heat will be lost through it at a much lower rate.

Experiments performed in a fully controlled environment (3) showed a reduction in the energy consumption of the test room of 3.7% when simple foil was used. When foil+insulation and patented foil panels were used the results were 4.4% and 6.1%, respectively. The walls were constructed of timber framing covered with plywood panelling and infilling insulation of 100 mm mineral wool. The savings would have been bigger had poorly insulated walls been used. The author mentioned the not so impresive performance gains the patented version achieves compared to the poor man solution. On the other hand, also pointed out was the possible effect the shaped panels (patented solution) may have in the temperature distribution of the room, making it more homogenous and further reducing the overall energy consumption.

From the article (3):

[...]Thus, for a very small outlay, significant energy savings can be made and a rapid return on the capital invested is achieved. In the test room used, which is the size of a small bedroom or sitting room, the total energy saved in a typical year in the UK's climate would be of the order of 60 kWh, i.e. a saving of £3 at current prices[...]For a typical three-bedroom semidetached house, the total annual saving would be of the order of 360 kWh, i.e. about £18, for an initial capital oulay of about £3. For poorly insulated walls, the energy saving is higher. (1995)

But this is not all to it; in (2), the variation of the heat output of radiators caused by altering the emissivity of the wall behind them was studied. They found that, if instead of a highly reflective surface (the foil), a highly emissive one is used (plain walls themselves are pretty emissive materials), the heat output is actually increased.

From article (2):

The results imply that the heat transfer rate can be increased by 20% through the use of a black [high emissivity material] instead of a reflective wall[...]An extrapolation indicates that the output of a single bank (plate) radiator will be increased by 10% and a double radiator by 5%. Wall surface temperature results indicate that a reflective wall does indeed decrease the heat loss through the wall.

All this is explained by the fact that a warm wall behind the radiator (the high emissive coating) is, effectively, an extra surface to heat up the air of the room by convection. So, increased heat output rate but also increased heat losses. The last two paragraphs of this article:

Current thinking is to place a thin sheet between the wall and the radiator that is reflective on the wall side and absorbent on the radiator side. This work provides a strong indication that this is a good approach. In conclusion, this work shows that putting a reflective sheet behind your radiator will reduce the running costs, but it will also reduce the heat output! It will certainly decrease the heat loss through the wall.

As a side note for the curious, the results in (2) led to the theoretical design of a better performing radiator, basically consisting in removing the fins from a double sided radiator and fitting in the inner gap one or two highly emissive sheets. These would be heated by thermal radiation and therefore heat the sorrounding air by convection, increasing the heat exchanging available surface and the warm air flow rate. All this with the advantage of being less prone to fouling (in a matter of months, dust in the fins can reduce the heat output of a radiator by 20%) and easier to clean (4).

Happy foiling.

Jose



(1) Pimbert, S.L., Reflective materials behind radiator shelves save energy. Building Services Engineer, August (1977) A22-3.

(2) Beck S.M.B., Blakey S.G, Chung M.C., The effect of wall emissivity on radiator heat output. Building Services Engineer Research and Technology, 22, 3 (2001), 185--194. http://bse.sagepub.com/cgi/content/abstract/22/3/185

(3) Harris D.J., Use of metallic foils as radiation barriers to reduce heat losses from buildings. Applied Energy, 52 (1995) 331--339. http://bse.sagepub.com/cgi/content/abstract/22/3/185

(4) Beck S.M.B., Grinsted S.C., Blakey S.G., Worden K. A novel design for panel radiators. Applied Thermal Engineering. 24 (2004) 1291--1300. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V1T-4K42DTD-1&_user=333848&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000017279&_version=1&_urlVersion=0&_userid=333848&md5=ae9bbc720cbf9e597f82fc0fc0da6b1f

silvercar

Current thinking is to place a thin sheet between the wall and the radiator that is reflective on the wall side and absorbent on the radiator side. This work provides a strong indication that this is a good approach. In conclusion, this work shows that putting a reflective sheet behind your radiator will reduce the running costs, but it will also reduce the heat output! It will certainly decrease the heat loss through the wall.

If that is true I've been doing it wrong.

I put the insulated side touching the wall and the reflective coat nearest the radiator.

My double sided tape has dried out after a year and a lot of the sheets are flapping too near the radiator.:(

kernel_panic

Current thinking is to place a thin sheet between the wall and the radiator that is reflective on the wall side and absorbent on the radiator side. This work provides a strong indication that this is a good approach. In conclusion, this work shows that putting a reflective sheet behind your radiator will reduce the running costs, but it will also reduce the heat output! It will certainly decrease the heat loss through the wall.

If that is true I've been doing it wrong. I put the insulated side touching the wall and the reflective coat nearest the radiator.

Not necessarily wrong. For energy saving purposes, you did exactly the right thing. The reason why they point out that the reflective sheet should be on the side of the wall is that this way, according to their findings, you would not only be saving energy due to less (almost zero) radiative losses, but also you would not be decreasing the overall heat output of your radiators.

Now, an article from a journal is not a DIY manual, they are not trying to tell people how to fiddle with foil sheets and cardboard boxes. My opinion, based on _my understanding_ (take it with a grain of salt), is that simply flipping the sides of a home made insulation+foil panel (let's say cardboard+foil) will not be such a great idea. In that configuration, i.e. foil nearest to wall, the cardboard will be heated by the radiator and will contribute to the warming up of air by convection. At the same time, the foil will block any radiation coming from the cardboard, which is good. The downside is that foil is a good heat conductor, and, being in direct contact with the warm cardboard and the colder wall, some heat will be lost through it by conduction.

A solution would be to leave a gap between the wall and the foil or make a sandwich with two insulating panels and the foil, but that would probably make things more complicated than the majority of us are ready to face. After all, the attractiveness of this trick is that it saves some money with a minimal cost and effort. Since we don't have any numbers about it, I would stick to what we know it does have a positive effect, unless one has good manual skills and actually enjoys doing this sort of work.

Jose

silvercar

I was trying to maximise the heat output of the rads/ reduce the heat loss through the solid walls.

I have the ready made sheets - bubble wrap one side stuck to foil. Having the foil nearest the rad must reflect more heat and prevent the heat from being absorbed by the wall.

Incidentally, in a couple of rooms I have a desk against the radiator and have put the insulation sheets on the back of the desk!

aristote33

I just found this radiator insulation panel calculator.
http://www.magnu-save.co.uk/insulatingpanelcalculator2.asp

Could the ones who laready have their panel test it to see if the needs calculation (not the savings one) is somewhat correct?

For the newbies, it shows how important it is to measure all dimensions of targeted radiators before ordering.

Will

david_mclean_2

Just bought a set of Heatkeeper Panels from Green and Easy, which arrived a couple of days ago. They're extremely easy to fit (double-sided tape is included) and apparently Heatkeeper updated the design for this year, so hopefully the energy saving should be even greater than previously. They seem to have made a difference already to the temperature of the room, so I'll be very interested to how my next heating bill compares.

Green and Easy seem to offer the Heatkeepers at the best price and they were extremely helpful over the phone, so definitely recommended all round.

Robert2009

But what of the OP who was going to tell us how much money he saved?

Ever notice that the posters who come on here with weird energy saving ideas that are going to save a fortune never come back and tells us how much they saved.

Cynical me?