Radiator Foil

A simple and effective way of reducing heating bills is to fit reflective foil behind radiators.

How does it work?

The effect of foil is to reflect the radiant part of the radiators heat before it gets absorbed by the wall, this means the room heats up more quickly and so the heating is faster to respond. If the radiator is on an outside wall then fitting foil behind it will also help to reduce the amount of heat leaving the building.

Where is it best to fit the foil?

Fitting reflective foil will be beneficial behind any standard radiator, but it's effectiveness will be increased if one or more of the following applies:

    • The radiator is on an outside wall
    • The wall behind the radiator is made from masonry rather than a plasterboard partition
    • The heating is turned on and off frequently rather than being left on most of the time
    • The wall's surface finish is non reflective

Depending on the variables above the fitting of foil behind radiators could save between around 5% (if none of the above are true) and 12% (if all of the above are true).

How can I fit the foil?

The following text can be downloaded in PDF format at the bottom of this page. Thanks to Andy Walker as SURE Insulation for this guide.

Materials and tools

    • Reflective, insulated sheet which can fit between the radiator and the wall. This is often called ‘foil’ but in fact is typically a sandwich of an insulating material with aluminium foil on one or both sides.
    • Disposable plastic sheeting e.g. bin liners.
    • White paper tape, or masking tape.
    • PVA glue.
    • Scissors.
    • Pasting table.
    • Long ruler.
    • Latex gloves.
    • Radiator paintbrush or roller.

There are a number of types of foil available. The cheapest option is to use standard kitchen foil perhaps stick to a sheet of thin cardboard. This option works however it will be very vulnerable to damage especially in a public building or where laundry is often hung over the radiator to dry.

The preferred option is to use a material which is basically bubble wrap with a foil coating on both sides. This is more robust and also provides a small amount of insulation to the wall. This material is typically sold by builders merchants for a range of uses. The cheapest source we could find at the time of writing was here, although this does require purchasing a 25m roll. If you are in the Leeds area feel free to get in touch and see if we have any - we've often got a roll.

Method

Set up a work space with a pasting table and plenty of room. Temporarily fit a strip of plastic sheeting to cover the wall from 50mm below the top of the radiator and extending at least 150mm on either side (Fig 3). This sheeting is to protect the wall as the foil is fitted. Measure the radiator and the position of the brackets. Cut out a ‘foil’ piece which allows 10 to 15mm on either side of the brackets (Fig 2). Leave a 50mm gap between the top of the radiator and the top of the foil. Similarly leave a 50mm gap at the sides (Fig 1). This is to make the ‘foil’ less visible.

Figure 1: Foil cut-out.

Figure 2: Cutting out slots for the radiator brackets.

Figure 3: Temporary plastic sheeting attached to wall behind radiator.

Before gluing the foil it is best to test how it sits behind the radiator. Adjustments can be made to the length of the slots and other dimensions if need be.

Cover the complete back of the ‘foil’ with a generous coat of PVA adhesive (Fig 4). For difficult or uneven walls a continuous bead of “Stixall-type” tube adhesive can be applied around the edge of the ‘foil’. With two people hold the foil between you and slide it over the top of the radiator (Fig 5). Line up the slots with the brackets and lower the foil into position. Use the radiator paint brush or roller to apply pressure across the surface of the foil to ensure it is well attached to the wall. Remove the temporary plastic sheeting. Clean up any excess adhesive.

Figure 4: Brushing PVA glue onto the back of the foil.

Figure 5: Sliding the glued foil behind the radiator.

Figure 6: pushing the foil against the wall with a long-handled roller.

If the foil is not staying stuck to the wall then scrunched up paper can be carefully pushed down behind the radiator to hold it in place until the glue dries. Be careful to ensure that you have a means of retrieving the paper afterwards!

An additional benefit can be gained by fitting a shelf above the radiator. The shelf should be at least the length of the radiator, be at least 75mm above the top of the radiator and extend as far as the front edge of the radiator. This will encourage mixing of the rising warm air from the radiator rather than it going straight up to the ceiling. It is recommended to run a bead of sealant along the bottom edge of the shelf where it touches the wall.

Typical usage and task duration

We found that with 5 people it took us 3 hours to fit foil behind 17 radiators of varying size.