Almost nobody knows this, but placing aluminum foil behind radiators can noticeably lower heating bills

On connaît tous la sensation désagréable d’ouvrir sa facture de chauffage en plein mois de février. Les chiffres semblent grimper plus vite que le thermomètre dehors. Le radiateur tourne, le thermostat grimpe, et pourtant la pièce reste tiède, presque frustrante. On finit par enfiler un pull de plus et par râler sur “ce fichu chauffage qui ne sert à rien”.

Un soir, chez des amis, j’ai vu quelque chose d’étrange derrière leur radiateur du salon. Une sorte de panneau argenté bricolé, à moitié caché par un rideau. J’ai cru à un morceau d’isolant oublié par un artisan, ou à une tentative de déco très ratée. Ils ont rigolé, et m’ont répondu : “C’est juste du papier alu, tu vas rire, mais nos factures ont baissé.”

Sur le moment, j’ai trouvé ça trop simple pour être vrai. Un rouleau de cuisine qui ferait baisser la facture énergétique ? Quelques semaines plus tard, en regardant mes propres radiateurs collés au mur glacé, j’ai commencé à douter. Et si ce petit geste bricolé valait bien plus qu’il en a l’air.

Why aluminum foil behind radiators actually works

Walk into any older flat in winter and you’ll notice the same thing. Radiators lined up against icy exterior walls, bravely pumping out heat… straight into the brick. You feel warmth in front of them, but the wall behind is cold to the touch. That’s lost money, seeping slowly through the masonry into the street.

Most standard radiators don’t just heat the air. They also radiate warmth in every direction, including backwards. Without anything reflective behind them, a surprising portion of that energy is simply absorbed by the wall. The result: your boiler works harder, your room warms slower, and your bill climbs quietly, month after month.

Aluminum foil changes the geometry of that heat. Instead of letting warmth vanish into cold plaster, the foil bounces a chunk of that energy back into the room. It’s not magic, it’s physics. You’re not creating more heat, you’re wasting less. And in a world where every kilowatt-hour is getting pricier, that tiny shift matters a lot more than most people think.

Take an old brick house with high ceilings, single-glazed windows and radiators bolted to exterior walls. Classic energy sieve. A UK housing charity once estimated that simple reflective panels behind radiators can cut heating energy use by around 5 to 10% in the right conditions. That doesn’t sound huge, until you translate it into a full winter’s worth of gas or electricity.

If your yearly heating bill sits at, say, £1,200, even a 7% reduction means more than £80 back in your pocket. Not from a fancy new boiler, not from smart thermostats or connected valves. From a roll of foil that usually lives next to the baking paper. It’s almost annoying how low-tech the idea is.

I spoke to a young couple in a drafty rented flat who tried it one Sunday, just to see. They cut pieces of thick foil, taped them behind the two main radiators, and forgot about it. A month later, their smart meter graph showed a noticeable kink: same thermostat settings, slightly lower daily consumption. Their comment was simple: “It feels like we turned the heating up by half a degree, without touching the dial.”

What’s happening is surprisingly straightforward. Radiators warm a room in two ways: heating the air around them (convection) and sending out infrared radiation. Without anything reflective behind, that radiation hits the cold wall and gets absorbed. The wall warms slightly, then leaks that heat outside through conduction.

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Stick a reflective surface behind, and a portion of that energy is bounced back into the room. The foil doesn’t warm up much, it just acts like a mirror for heat. You’re nudging more of the radiator’s effort toward the space you actually live in, rather than the bricks and the pigeons. Over hours, days, weeks, that small tweak becomes a real difference.

There’s also a psychological twist. When a room feels more evenly warm, people are less tempted to crank the thermostat “just a bit higher”. One degree less on the dial can mean around 7% savings on heating in many homes. So a simple strip of foil doesn’t only change physics, it can gently change habits too.

How to actually do it without ruining your walls

The basic move is almost embarrassingly simple. You take aluminum foil, the shiny kind you wrap over a lasagna, and place it between your radiator and the wall, shiny side facing the room. The goal: create a reflective “curtain” that isn’t visible from the front, but quietly works in the background.

The easiest method is to use a thin, rigid backing. A piece of cardboard, a leftover bit of foam board, even part of an old moving box does the job. Wrap it in foil, tape it at the back, then slide the panel down behind the radiator. The foil shouldn’t touch the hot metal; it just needs to sit a few centimetres away, catching that radiant heat.

If your radiator is fixed very close to the wall, you might have to cut narrower strips and slide them one by one from above. It feels a bit like posting letters into a slot. Not glamorous, but once they’re in place, you forget they exist. Until the next bill arrives.

There are a few traps that many people hit on the first try. One is taping the foil directly to the wall, with no backing. It works in theory, but looks terrible when you remove it, and the foil tears easily. Another mistake: crumpling it too much. A slightly uneven surface is fine, but a ball of wrinkles reflects less and collects dust.

And then there’s the “I’ll do all the radiators, right now, before dinner” impulse. Real life laughs at that. Start with the rooms you heat the most: living room, main bedroom, kids’ room. One radiator at a time, over a few evenings. *Tiny, boring steps often beat huge ambitious plans that never happen.*

Think about curtains and furniture too. A big sofa pressed tightly in front of a radiator blocks both heat and any benefit from the foil. Leaving a small gap, even 5 to 10 cm, lets air circulate. Same with long curtains that cover the entire radiator: they create a warm bubble between fabric and metal while you shiver in the middle of the room. Soyons honnêtes : personne ne réorganise son salon juste pour un radiateur, but nudging a chair or lamp 20 cm can already help.

When I asked an energy advisor what cheap fix they’d recommend first in an old flat, they didn’t hesitate:

“People dream of heat pumps and triple glazing, but many are still throwing good money straight through cold walls. Reflective panels or even simple foil behind radiators are like picking up the banknotes lying on the floor before you talk about big investments.”

There’s something oddly comforting about a solution that doesn’t require apps, subscriptions or installers. Just your hands, a bit of foil, maybe a pair of scissors.

• Use thicker foil if you can: it tears less and holds shape better.
• A backing panel (cardboard, thin foam) helps keep things flat and removable.
• Keep a little gap between radiator and wall for air to move.
• Don’t block the radiator front with heavy furniture or enormous curtains.
• Check once a year that the foil is still clean, dry and in place.

What this tiny hack says about the way we heat our homes

We’re living in a strange moment where energy has never been so talked about, yet many of the most effective moves are almost invisible. Governments debate megaprojects, companies sell connected thermostats, and somewhere in the middle, a roll of kitchen foil quietly helps a family shave a few euros off their monthly bill.

There’s also a deeper, almost emotional layer to it. On a cold evening, when the rain hits the window and the wind squeezes through old frames, having a home that actually holds onto its heat feels like a form of dignity. On a tous déjà vécu ce moment où l’on se demande si on va rallumer le chauffage ou juste enfiler un quatrième pull. Knowing that your radiators aren’t wasting half their effort into the wall changes that inner negotiation, even a little.

What’s interesting with the foil trick is not just the saving itself, but the mindset it opens. Once you’ve done it, you start seeing other leaks differently. That gap under the door. The always-open vent in the bathroom. The window that never quite closes. A low-tech fix behind a radiator has this side effect: it turns you into a quiet detective of your own home.

And it spreads. Someone notices the silver glint behind your radiator during dinner, laughs, asks why. You explain, half amused, half proud. They go home and look suspiciously at their own walls. A few weeks later, they message you: “Alright, you were right, our place heats faster now.” That tiny act of passing on a simple, almost silly trick might be one of the most practical gifts you can give this winter.

Table: Key points of the foil trick

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