Do Thermal Curtains Work in the UK? Heat Loss, Savings & When They Help

How do thermal curtains reduce heat loss?

Windows are often one of the colder surfaces in a room. Energy Saving Trust says around 18% of the heat in a typical uninsulated home can be lost through windows. Thermal curtains add another layer between the warm room and the cold glass, slowing heat transfer and reducing the cold air movement that can make the area around a window feel uncomfortable.

The lining matters because it increases thickness and reduces air movement through the fabric. The trapped air between the curtain and the window also acts as an extra insulating layer when the curtain is closed.

When do thermal curtains make the biggest difference?

They are most useful when the window itself is a noticeable cold point in the room. Typical examples include:

• single-glazed windows;
• older double glazing that still feels cold at night;
• large glazed areas such as patio doors;
• bedrooms where people sit or sleep close to the window;
• rented homes where replacing windows is not realistic;
• rooms where draught-proofing has already been done but the glass still feels cold.

If you can actually feel moving cold air around the frame, deal with the draught first. See How to Draught-Proof Doors and Windows UK for the correct approach.

How much can thermal curtains save on heating?

There is no reliable UK-wide figure that tells you how many pounds a year thermal curtains alone will save. The result depends on the glazing, curtain size and fit, how long they stay closed, outside temperature, heating schedule and the amount of heat the window was losing in the first place.

Energy Saving Trust recommends heavy, lined curtains as an affordable quick fix for helping a home retain heat, but does not give a standard annual saving for curtains alone.

The more realistic benefit is that the room may feel less cold near the window, which can reduce the temptation to run the heating harder simply to compensate for a cold surface.

How to use thermal curtains effectively

Close them when the outside temperature drops

In winter, close curtains around dusk or when the window surface starts becoming noticeably cold. Open them again in daylight when useful solar gain is available.

Cover the full window area

A curtain that barely covers the glass leaves more room for warm air to circulate behind it. A wider pair with good overlap at the centre and enough coverage at the sides generally creates a more useful insulating layer.

Keep the top gap small where practical

Warm room air can rise behind a curtain, cool against the glass and fall back into the room. A pelmet, close-fitting track or other arrangement that limits this air loop can improve comfort, provided it is safe and practical.

Choose a substantial lining

Heavy lined curtains, blackout linings and dedicated thermal linings all add thickness. The label “thermal” matters less than the overall construction, fit and how consistently the curtains are used.

Should thermal curtains cover a radiator?

No. Energy Saving Trust specifically advises against blocking radiators with curtains because the heat then struggles to circulate into the room.

If the radiator sits below the window, the curtain should ideally finish above it or be arranged so warm air can flow freely into the room. Long curtains hanging directly in front of the radiator can trap heat between the fabric and the window instead of letting it warm the space.

Do thermal curtains help keep a room cool in summer?

They can also reduce unwanted solar heat gain when closed before strong sunlight reaches the room. Energy Saving Trust recommends closing blinds and curtains when the sun is shining through a window, especially during hot weather.

The key is timing: close them on the sunny side of the home before the room heats up, then reopen them when the sun has moved away or when outside air becomes cooler than indoors.

Thermal curtains vs other ways to reduce window heat loss

For a cold room, curtains are best treated as one layer in a wider plan. Start with How to Stop Heat Loss in a Room UK so you can identify whether the main problem is windows, draughts, floors, walls or heating distribution.

Who should consider thermal curtains?

• Renters: useful when permanent window upgrades are not an option.
• Bedrooms: helpful where cold glass creates discomfort near the bed.
• Older homes: especially where windows remain a cold surface after draught-proofing.
• Large glazed doors: useful for reducing night-time chill from wide glass areas.
• Budget improvements: a relatively low-cost step before major window replacement.

Ready to compare current options? See Best Thermal Curtains UK 2026 for thermal-lined, blackout, pencil-pleat and large-window picks. Prioritise good fit, substantial lining and safe clearance from radiators over marketing labels alone.