Heat radiates directly from behind your radiator into the outside wall, wasted. With thin reflector foil, you direct that heat back into your room. The effect is especially strong with older, uninsulated exterior walls.
Step by step
Every radiator radiates heat in all directions, also backward into the wall. With uninsulated exterior walls (typical before 1990), this backward heat radiation goes straight outside. A silver reflector foil (usually 4–5 mm thick, self-adhesive) redirects radiation with high reflection coefficient (>0.95) back into the room. Result: more heat energy stays in your house, your heating system can run for shorter periods.
Source: Stiftung Warentest, Reflector foil saves 4–15% heating costs, depending on wall insulation
Step by step
- Check the wall conditionLook at the wall behind your radiators. If it's an exterior wall (no windows, feels cold) and looks thin, reflector foil makes sense. With thick, insulated walls it helps less.
- Buy the foilSelf-adhesive reflector foil (from a hardware store, 4–5 mm thick) costs €15–30 per roll (5–10 m²). You need enough to cover the radiator plus 15 cm on each side.
- Prepare the wallClean the wall behind your radiator well (dust, old wallpaper). It must be dry. Remove loose pieces. Best: remove old wallpaper until you see textured wall or plaster.
- Cut the foilMeasure the radiator rectangle (height + 10 cm top + 10 cm bottom, width + 10 cm each side). Cut the foil, and remember you can't cover the back of the radiator itself.
- Apply the foilPeel back the backing and stick the reflector foil directly on the wall. Press it firmly to avoid air bubbles. Make sure the foil doesn't go into or behind the radiator.
Worked example
Before: Old building with uninsulated exterior wall behind the living room radiator. Wall is cold (13 °C in winter). Heating costs €2,000/year.
After: Applied reflector foil (€30), wall interior temperature rises to 17 °C from reflected heat radiation. Heating system runs for shorter periods. Savings 8–10% (about €160–200/year with uninsulated wall). Pays for itself in 3–4 months.