Reflect heat back into the room — and let your radiators run hot
Two ten-minute jobs make every radiator earn its keep: reflective foil stops heat vanishing into a cold outside wall, and bleeding releases the trapped air that leaves the top stone-cold.
Radiators are simple, but two quiet faults stop them delivering the heat you’re already paying for. The first is trapped air: as a heating system ages, air collects at the top of radiators, leaving them hot at the bottom and cold up top. The boiler keeps pumping, the room never quite warms, and you nudge the thermostat higher to compensate. Bleeding releases that air in a couple of minutes and lets hot water fill the whole panel again.
The second is heat escaping backwards. A radiator on an external wall radiates a good share of its warmth straight into the masonry behind it — and on an older solid wall, much of that simply leaks outside. A reflective sheet on the wall bounces that heat back into the room where you want it, for the price of a coffee.
Neither job is glamorous, and neither will transform a poorly insulated home on its own — foil helps most on solid, uninsulated walls, less so where there’s already good insulation. But together they’re a genuinely free-ish way to get more warmth from the same boiler run. Do them once at the start of the cold season, alongside keeping furniture and washing clear of the panels, and your heating quietly works less hard for the same comfort.
How to do it
- Feel each radiator after the heating's been on a while. If the top stays cold while the bottom is hot, there's trapped air — it needs bleeding.
- Turn the heating off and let the radiator cool. Hold a cloth or cup under the bleed valve at the top corner and turn the square key (a €2 part from any DIY shop) anticlockwise a quarter-turn.
- Let the hissing air escape; the moment water dribbles out, close the valve firmly. Top up your boiler's pressure afterwards if the gauge has dropped below about 1 bar.
- For radiators on an external wall, cut reflective radiator foil (or kitchen foil on card at a pinch) to size and fix it to the wall behind, shiny side facing the room.
- Make sure nothing blocks the heat: pull sofas and long curtains clear of radiators, and don't drape wet washing over them — it forces the boiler to work harder.
Pro tips & pitfalls
- Bleed radiators from the lowest in the house to the highest, and the downstairs ones before upstairs — air rises, so you'll clear the system more thoroughly.
- Purpose-made radiator foil has an insulating backing that beats bare kitchen foil, which tarnishes and reflects less over time. It matters most on solid, uninsulated outside walls — on a well-insulated cavity wall the gain is smaller.
What it's good for
Good for the planet
- Saves energy A bled radiator heats fully instead of half-cold, and foil stops warmth conducting straight into a cold external wall — so the boiler reaches your target temperature sooner and cycles less.
- Cuts CO₂ Every minute the boiler doesn't run is gas not burned — small per radiator, but it adds up across a whole heating season.
Good for you
- Saves money Reflective foil behind radiators on outside walls can trim a slice off heating bills, and both jobs cost only a few euros in materials.
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