Radiator reflector panels: the 20% saving nobody can verify

Radiator reflector panels: the 20% saving nobody measures

A serrated aluminium panel, five units per box, heat-resistant double-sided tape and the promise of cutting heating bills by up to 20%. The product is sold as a scientific solution for water and electric radiators, based on the idea that radiant heat currently lost through the wall is reflected back into the room. The question that comes up in every conversation on the subject is not whether the gadget works, but whether the price paid for it makes any sense.

What a heat reflector panel actually does

The physics is simple: a radiator emits heat through radiation, convection and conduction. The radiant part heats the wall behind it, and that wall, if it faces outside, becomes a heat sink towards the street. A panel with a metallic surface reflects that radiation back into the room and, at the same time, breaks the thermal bridge with the wall. So far, the manufacturer's argument holds up.

The problem is the magnitude. The promotional material itself claims energy savings of up to 20% in an average home with radiators in every room. None of the people who have tried the gadget at home have been able to confirm that figure. Some argue that the improvement exists but is modest, while others have noticed no difference at all in the temperature of the coldest room.

Vaccine boxes and car sunshades

The most popular alternative is not bought: it is recycled. Insulated boxes used for medical transport, with thick cardboard and a thin metallic coating, do the same job. Those who have placed them behind radiators describe the wall to the touch as "very cold", which is exactly what you want. The cost is zero and installation takes a few minutes.

Along the same lines, a cut-up car sunshade or a sheet of aluminised bubble wrap serves the same purpose. The price range is wide: from a six-metre roll for 7.99 euros at a supermarket chain to aluminised insulation at 54 euros for eight metres at a DIY superstore. The difference between paying eight euros or fifty-four for the same physical principle is probably the most useful piece of information in this whole affair.

Why aluminium alone is not enough

Metal reflects, but it also conducts. An aluminium panel stuck directly to the wall ends up transmitting heat to the wall by conduction, which reduces the insulating effect. The solution that keeps coming up is to insert an insulating layer between the metal and the wall: cardboard, white cork, polystyrene or polyamide. The latter, used in aluminium joinery with thermal break technology, is suggested as the most durable material against moisture and condensation.

There is a nuance that changes the calculation depending on where the radiator is. If the wall faces outside, the saving is real. If it faces another room inside the home, the heat absorbed by the wall is later released into the adjacent room. The panel still makes sense, but the benefit is diluted.

The case of electric radiators

The bill that comes up in the conversation helps explain why anyone would bother putting cardboard behind a radiator. Two months of electric heating, with two twelve-element programmable units and two more without a programmer, totalled 819 kWh and 93.60 euros. And that without it having been really cold.

With numbers like those, any measure that cuts consumption has immediate appeal. The question is whether the reflector panel is among them or whether it just moves heat around. The honest answer, judging by the testimonials, is that nobody has measured it rigorously.

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The product is still sold with the label of scientifically proven savings. Those who have installed it at home, at best, sense an improvement they cannot quantify. Those who have not are left with a roll of aluminised plastic, an empty vaccine box and the same cold wall to the touch.