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Around half of your heating could be lost through your walls

David Farmer is a research fellow at the University of Salford who manages the Salford Energy House – an actual, fully-furnished house that sits inside a giant environmental chamber. By changing the temperature and even weather around the house, he and his team have been able to test factors that affect heating loss from a home.

The Energy House is designed to mimic a house at the end of a terrace, and 55% of its total heat loss is through its walls. Any typical uninsulated end-of-terrace or semi-detached home might similarly see around half its energy lost this way. For a mid-terrace single-glazed home you might lose more heat through the windows. In general, the crucial factor is going to be heat loss through the largest uninsulated outside-facing part of your home.

Another factor is how airtight your home is. However, we always need to maintain ventilation. David explains: “Some ventilation is specifically for indoor air quality purposes or if you’ve got an open fire.” We also generate a lot of moisture – through cooking, showers and drying clothes – and without ventilation the condensation can cause mould growth. When insulating, it’s important never to block up intentional ventilation points like fans.

A third factor is how efficient your heating system is.

Adding insulation to the inside and outside of your house is very expensive

For an old house like Robin’s, with solid walls, cavity wall insulation isn’t an option.

“You’ve either got to put insulation on the inside or the outside, and that becomes quite expensive,” explains David. Done to building regulation standards, it can reduce the heat loss of your house by about 40% – but could set you back around £10,000.

“The reduction in heat loss of double-glazing windows is over 50%,” says David. But again, replacing windows can be very pricey. So what are the more affordable options?

Thermal window film is a fiddly but cheaper option

Thermal films are thin, flexible sheets of plastic that you pull over your window, stick to the frame and then heat with a hairdryer to remove wrinkles and create a seal.

There are countless versions available online, with the cheapest costing only £1 to £2 per square metre.

“Effectively it does two things,” David explains. “It creates that seal, which prevents drafts coming through the window frame itself, and you get very still layers of air on each side of that plastic and that actually reduces the heat transfer through the window.” The Energy House team measured reductions in heat transfer, through a single-glazed window, of around 25%.

Though fiddly to install, it could be worth the effort. “When we’ve looked at the actual reductions in energy loss resulting from these films, we found a 3% reduction on a winter's day,” says David. It could pay for itself.”

However, he suggests you give it a miss if your windows are double-glazed: “Double glazing is relatively well performing so those big savings that we measured for single glazing aren’t necessarily going to apply.”

Magnetic glazing may not be any better than plastic film

An alternative is secondary magnetic glazing, where a large acrylic sheet covers the window and is magnetically attached to the window frame.

This option is more expensive. One company quoted £40 per square metre, depending on the thickness of the plastic, plus £25 for a roll of magnetic tape.

However, it may not be more beneficial than plastic film. “Even though it’s going to be a lot thicker, most of the heavy lifting in terms of reducing heat loss is by creating that still air between the actual secondary glazing and the window itself,” states David. “Also, those thin films of air that are on either side of the plastic will be pretty much the same for both products.”

“What it might provide though is a more robust and long-term method of actually sealing that window,” he says. It’s easier to remove and replace, which is helpful come summer or if you need extra ventilation.

However, a thermal blind like this costs in the range of £300 per square metre so this is an expensive option.

Radiator backings reflect heat back into your room

Thick curtains and thermal blinds can similarly reduce the air infiltration around windows, says David, and create extra resistance in terms of the passage of heat.

“We have measured blinds that have thermal properties and they have reduced the heat transfer through our single-glaze test window by a factor of four,” or over 75%. When the blind’s closed there’s a quarter of the amount of heat that’s passing through the window, compared with when its open.” So, when the nights are long, you could be making some savings. “Heavy curtains would certainly do a similar job,” he suggests.

David says that even a traditional roller blind, on a double-glazed window, could incur a 10% saving (compared to when the window has no covering at all).

A range of draught-proofing products can make a difference

There are a vast range of draft-excluding products on the market: tapes for as low as £1 per metre, £10 per metre silicone draught excluders and door brush seals for around the £6 mark. There are even inflatable bags that you can put up your chimney.

A lot of simple, DIY interventions can make a difference, says David. For homes with suspended timber floors, where there’s a draft between the skirting board and the carpet itself, a draft-proofing strip can certainly help.

“We’ve done some draft-proofing work and reduced the air infiltration rate by about 40%,” he says.

Carpet underlay helps to add airtightness to your floors

A carpet underlay will help reduce air movements through wooden floorboards, says David. Fit it right into the corners of the rooms, to provide some airtightness.

It could also be worth investing in a better-quality carpet. Tests in the Energy House showed that ordinary carpets reduced the heat loss of the house by about 3%. When they laid a new, higher-quality carpet, that figure increased to 5%.

Thermal wallpaper and paint are costly but not that effective

David’s team tested a 10mm, latex sponge thermal wallpaper and found it reduced the heat transfer through the wall by over 30%. However, it’s not cheap at around £50 for a 10-metre roll. “The payback times are likely to be quite long,” says the researcher.

Thermal paints (around £25 a litre) should be avoided. Some claim to be highly heat reflective but David and his team found no evidence of this: “I think we’re more inclined to call them magic paints because they don’t work!”

Small incremental gains can add up

“It’s about these marginal gains and the accumulative marginal gains that we can get through some of these measures,” David stresses. With all these small hacks done correctly, you could be looking at between a 5 and 15% reduction in energy use. “If you’re planning on staying somewhere for a little while, these products will probably pay for themselves after a couple of heating seasons.”

Although, not the thermal paint: “That’s definitely BS!”

To find out which insulation methods Robin is going to try out, listen to the full episode on 91Èȱ¬ Sounds.