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Cheap radiator reflectors to lower your fuel bills

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Central heating radiators do a good job of warming the wall behind them, which isn’t a great use of energy particularly if the radiator is on an uninsulated outside wall.  A reflector positioned behind the radiator will save some of this wasted energy, meaning that the room should heat up quicker and the boiler will consume a little less fuel in maintaining the temperature.  The savings will not be great, but even a small saving is worth having – if you can get it cheaply.  And since this project makes use of cardboard boxes that can be obtained for free, it is very cheap.

The UK’s Energy Saving Trust (an independent organisation that works in partnership with the government and other bodies to provide energy efficiency advice in the residential sector) currently recommends two manufacturers’ radiator reflector products (see here: http://www.energysavingtrust.org.uk/Find-Energy-Saving-Trust-Recommended-Products/browse/insulation/radiator-reflector-panels).  Buying enough of the cheaper product to suit 6 “average” radiators (which might just be enough for a small house, if you only treat the radiators on outside walls) will cost £18 including delivery.  But if you live in a solid-walled old house like mine, your radiators (and energy bills) will be rather bigger than “average” and you would need to spend considerably more.  This Instructable shows how to make cheap and cheerful reflectors from corrugated cardboard and sunshades, windscreen protectors or metallic plastic film.  They scarcely show when they are in place and they can easily be removed for cleaning – it’s a good idea to do that at least once a year, at the start of the heating season.

There is some merit in fitting reflector panels behind radiators on internal walls too, and on external walls that are insulated, but the savings will not be as good so do the external uninsulated walls first.

Materials and tools
  • Cardboard cartons or other source of corrugated card
  • Reflective silver coated material
  • Electricians’ tape (preferably in a colour that matches the decor) or decorative silver sticky tape
  • Double sided tape or a stapler
  • File spines/binders of the slide-on type (optional)
  • Bamboo kebab skewers or wooden cocktail sticks (may not be required)
  • Craft knife and straight edge
  • Rule/measure
  • Big cutting mat or a pile of newspapers
  • Pencil
  • Pen that will write on your reflective material
 
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The only thing I wonder about is the actual increased efficency, static radiators use the warmed air to draw cooler air in from the bottom, if this flow is restricted the actual warming ability will be reduced, using the percentage wall space with the extra insulation compared to the whole it would seem like you might be heading for a cooler room.
If your reflective addition reduces air flow then you may have reduced heat transmission by 1/4, this would mean longer boiler cycle times.
Yorkshire Lass (author)  longwinters1 year ago
It certainly wouldn't be good to restrict the airflow behind the radiator unduly. As you say, it may take longer to get the room up to temperature and it may never make it on really cold days. However, the independent Energy Saving Trust only recommends reflectors that produce minimum savings of 75kWh/m2/year, and 2 products are recommended so we know that savings at this level are achievable.  Their test method (see here) requires an 80mm gap behind the radiator.  In my house the gaps are just over 40mm, but that still leaves quite a lot of room for a reflector, even if you leave a small air gap behind it to reduce the condensation risk (see Dec 12 comment below).  Also, most of my rads are the double panel type with a central gap (maybe that is why you talk about a reduction of 1/4?), which will reduce the impact of a small reduction in airflow at the back on the overall heat output.  Before I started mounting the reflector foam on corrugated card, it would unstick itself from the wall and snarl up, and that really did block the airflow at the back. 
Melibokus2 years ago
excellent and cheap (brings more than it costs). You can also use the wrapping of liquids like tetrapak. I compound of paper, PE polymer and alu. The PE is hot meltable.
With whitelime (PVA) you can paste it.
The effect is, the IR part of warmth is reflected and not lost. The other part is convection. The convector leaves more heat.
But , in turning this gain, the wall behind the shield leaves colder. You shall keep in mind the dewpoint. If water condenses behind, mould can make problems. But, without the shield the mould comes on an other place.
Yorkshire Lass (author)  Melibokus2 years ago
Thanks for your comments. Using Tetrapacks is a really good idea, more diversion from landfill (which is where most of them end up in the UK).

The dewpoint issue is a valid one, and is probably why one (at least) of the 2 Energy Saving Trust-recommended proprietary panels comes with the recommendation to leave a gap between it and the wall, as well as a gap between it and the radiator. Then there shouldn't be a problem, because the wall behind the radiator will be much the same temperature as the rest of that wall, and it seems unlikely there would be any substantial condensation on it unless the room is very damp. (And cold winter air entering the house will have a low moisture content, and therefore a very low humidity once it is heated by the dry heat of radiators.) In my 9" brick walled house I get some condensation on the (double glazed) bedroom windows, but none on the inner surface of the walls. The best solution to condensation is ventilation, so throw open the windows for an hour or two every day when the heating is off, if necessary.
pudtiny2 years ago
I have used heavy duty kitchen foil for years and never had an oxidation problem. My parents used this and radiators that have been on walls for decades didn't show significant oxidation if any. But what ever you use its worth doing
Yorkshire Lass (author)  pudtiny2 years ago
Pudtiny, I quite agree - whatever you do is better than nothing. The oxide coating on aluminium isn't easy to see, it shows as a slight dulling of the surface instead of a mirror finish. Some people just stick foil behind their radiators. I think it's better to use foil-covered cardboard panels because they are easy to ft and to remove for cleaning or redecorating, and the cardboard provides a little extra insulation. Dust will soon reduce the reflectivity so it is important to keep them clean. (And don't forget to clean the condenser coils at the back of your fridge while you are at it.)
Doesnt
Radiant heat heat the entire room rather than the air itself?
The point of a hot water system is to load up a whole bunch of material with energy so that it takes a long time for that heat to come out into the air.
Temperature swings in old hot water systems should generally stay within 5 or so degrees or so forever.
Your wall behind the radiator should kind of hold some of that heat energy for the air to slide along & catch via convection.
Yorkshire Lass (author)  dreiseratops2 years ago
Radiant heat travels in straight lines, so the radiant component from the back of the radiator heads straight for the wall. When it gets there, much of it will be lost to the outside by conduction through the wall, because heat flux is greatest where the temperature difference is greatest, and the outer surface of the wall is a lot colder than the interior of the room. Reflecting the radiant component back keeps the water in the radiator hotter than it would otherwise be, meaning that the boiler doesn't need to fire as often in order to maintain the temperature that the return thermostat in the boiler is set to achieve.

Most people (here in the UK at least, where energy is very expensive) only run their central heating systems for an hour or two in the morning and another hour or several at night. The main object of the exercise is to heat the air within the rooms, not the fabric of the building, since it is principally air temperature that makes us feel comfortable (or not).

Myself, I'd rather heat the room than the birds outside!
I kinda wondered about that but was at work & unable to further elaborate. That is where the insulation is kept though.
What you say makes perfect sense. Though I always wondered why they put the radiator under the windows where the energy loss is greatest. I like the idea of in floor hot water too.
Im just getting into the whole science as Ive been working tech support for honeywell for about 2 months now. I got basic system setup nailed down but not the uber engineering & thought water storing up a lot of heat & disipating it through the day was the deal but having a timed stat type system might waste energy in that setup Vs. GFA. If you heat the air you only heat the air. If you heat the objects the objects in turn heat the air while taking longer to warm up it takes longer to cool as well.
They remain insulated against drafts... Yes? Kinda? Maybe?
Yorkshire Lass (author)  dreiseratops2 years ago
Radiators are usually put under windows precisely because that is where the energy loss is greatest, and where fresh, cool air is most likely to infiltrate the room. The theory is that fresh air leaking through the windowframe will pass over the radiator and be heated as it rises up into the room, so avoiding cold draughts. Even if there is no air leakage, the windows usually have a higher U value (ie greater heat transfer per unit area and temperature difference) than the walls, so they will be the cool spots in the room. If you put the radiator somewhere else, the area in front of the window will be decidedly chilly and you end up with a big temperature gradient acrosss the room and part of it that is essentially unusable. But in a modern, well insulated building with high performance windows there is less reason to put the radiators in the conventional under-window position.

Under-floor heating makes a lot of sense in a well insulated building, and it works well with heat pumps because it suits the lower temperature. If you have electric heating on an overnight, economy tariff then you definitely want a building with a high thermal mass that will absorb the heat and release it slowly during the day. Modern buildings tend to be of more lightweight construction and they heat up and cool down relatively fast compared with, say, an old stone-built property with solid internal walls.

Studies have shown that it is more cost-effective to have central heating on a timer to cut in and out once or twice a day than leaving it on all day. When you think about it, if the entire fabric of the building is kept warm all the time, the heat losses will be that much greater because hot bodies lose more heat than cool ones. You are, in effect, paying to heat bricks and plaster that you don't normally come into contact with as well as heating the air that will actually make you feel warm.

Domestic heating and the related energy consumption are not simple, there are so many variables. However, two things that are always worth doing are stopping draughts and improving insulation, especially as energy prices keep rising. So stick some cheap, home-made reflectors behind your radiators!
lol
I see. *bow
I'll keep that in mind when I am charged to replace a thermostat next week-month.
Would a windshield sun shade be a good way to go?
Also what do you know of this plastic film business? Is there anything specific to look for in doing that job?
Yorkshire Lass (author)  dreiseratops2 years ago
I think a windshield sunshade would do very well, as long as it is of the mirror-like, super-shiny type. As for film, choose one with the highest reflectivity you can find but read all the info. from the supplier to check for other problems such as a tendency to wrinkle or a need to keep it dry. I have some space blankets on order from Amazon that I plan to use for my internal radiators, I'll post again when I have used them.
Kiteman2 years ago
Putting reflectors behind radiators is the most cost-effective method of home insulation - whilst double-glazing might take twenty years to pay back, a layer of kitchen foil behind your radiators pays back in about 9-10 months.