Close your curtains at 7:45 pm to help lower your heating costs.

With the start of spring, many people are reluctant to turn the heating down, even though the weather is clearly getting milder. As soon as night falls, homes cool quickly and the thermostat clicks back on. A surprisingly simple habit at around 19:45 tackles that exact problem - with no new boiler, no smart-home gadgets and no major renovations.

Why keeping an eye on the clock suddenly matters

In March, the days stretch out, the sun stays up for longer and it naturally warms your rooms. Your windows act a bit like a magnifying glass: they let sunlight in and the indoor air heats up - but once the sun disappears, the glass also becomes a route for heat to escape back outside.

If you close your curtains early enough in the evening, you can significantly slow heat loss through the windows and reduce energy use.

In many parts of the UK, the sun goes down at roughly 19:45 around this time of year. From that point onwards, the benefit flips: windows start cooling fast and the warmth you built up during the day begins to leak away. Leave curtains open and you’re effectively “heating” the outdoors.

The idea is simple: let the sun do the work in daylight, then seal things up at the right moment in the evening. That way, free daytime warmth stays in the room for longer - and your heating either comes on later or not at all.

How much does it really make a difference to heating costs?

Windows are widely seen as one of the weakest points in a building’s fabric. Even modern glazing typically loses far more heat than a well-insulated wall. Curtains are not insulation in the same way, but they do create an extra layer of trapped air.

That air gap has practical, measurable effects:

• The inside surface of the window cools down more slowly.
• Cold air dropping down from the glass is reduced.
• The room feels warmer, even if the thermometer barely moves.

Feeling just 1–2 °C warmer can be enough to nudge the thermostat down slightly. And as a rule of thumb, each degree lower can cut heating energy by around 6% on average. Across a month, that can quickly add up to tens of pounds - and in a poorly insulated home, potentially much more.

The big difference: standard curtains vs thermal curtains (Thermovorhänge)

Not every fabric in front of a window performs the same job. Thin decorative panels may look nice, but they do little to hold warmth in. Thermal curtains (Thermovorhänge), on the other hand, are designed specifically to keep heat indoors in winter - and to keep summer heat out.

Type of curtain	Typical material	Heat-protection effect
Lightweight decorative curtain	Thin cotton, voile	Barely noticeable
Heavy fabric curtain	Thick cotton or polyester blend	Noticeable reduction in draughts
Thermal curtain (Thermovorhang)	Multi-layered, often with fleece or a thermal lining	Clearly reduced heat loss

Thermal curtains are usually built in multiple layers and may include a coating or a lining such as fleece or wool. They create a tighter seal around the window area visually and thermally - which is particularly noticeable with older windows that don’t insulate well.

Thermal curtains (Thermovorhänge): costs and everyday savings potential

A good-quality pair of thermal curtains can easily cost around £100. That can feel steep at first glance, but it makes more sense when you look at the long-term use.

• Lifespan: several years, often far longer than most people leave a heating system unchanged
  
• Usefulness: worthwhile every day of the year - warmth in winter, reduced overheating in summer
  
• Savings: fewer heating hours and less reliance on fans or portable air conditioning
  

In many households, that extra barrier is enough to avoid heating the bedroom at night entirely. Keep that up across a full heating season and the saved kilowatt-hours can gradually pay back the initial spend.

How the 19:45 rule works in real life (curtains and heating)

This only works properly if it becomes routine. If you wait until the room already feels damp and chilly, you’ve missed part of the benefit. The best approach is to build a repeatable habit around sunset.

1. During the day: open curtains wide so as much sunlight as possible reaches the room.
   
2. Early evening: keep an eye on the time - in March it’s often around 19:45.
   
3. By dusk at the latest: close all curtains and, if you have them, close blinds or shutters too.
   
4. Adjust heating: turn the thermostat down slightly and check whether your comfort level stays the same.
   

If you live in a flat with no shutters or external blinds, thick curtains can make an especially noticeable difference. In homes with modern triple glazing, the effect is smaller - but still meaningful, particularly in rooms with large window areas.

Extra comfort win: reducing draughts and condensation

Closing curtains at the right time isn’t only about heating costs. It can also improve comfort by reducing that familiar cold “fall” of air near windows and making seating areas by the glass feel less chilly.

It can also help with condensation control in a practical way: warmer internal surfaces and steadier indoor temperatures can reduce the conditions that encourage moisture to collect on cold panes. The key is balance - seal up at dusk, but still ventilate appropriately at other times of day.

Bonus in summer: keeping heat out instead of cooling it away

Thermal curtains aren’t just a winter tactic. Many designs work in summer in the opposite direction: they help keep outdoor heat from pouring in. The principle is similar - the timing simply shifts.

Air the room briefly in the morning, then close the curtains - and the midday heat stays outside for much longer.

If you ventilate properly early in the day while the air is cooler, then shut windows and close curtains, you reduce how much walls and furniture heat up. That can lower the need for fans or portable air-conditioning units. In that sense, curtains can also influence your electricity bill - indirectly but noticeably.

Common mistakes that cancel out the effect

Plenty of households have curtains, but use them in ways that undermine any energy benefit. These pitfalls are easy to avoid:

• Letting floor-length curtains cover a radiator - heat gets trapped between the curtain and the window.
• Keeping curtains open even though it’s already dark and getting cold outside.
• Using short or narrow curtains that don’t cover the full window area.
• Leaving windows permanently on the latch (tilted open) while expecting better heat retention.

Ideally, your curtain should cover the whole window and slightly overlap the frame, hang down to just above the windowsill, and sit in front of the radiator without completely blocking it.

How to estimate your own savings (roughly)

If you want a simple, low-effort test: pick two evenings with similar outdoor temperatures. On one evening, leave the curtains open; on the other, close them consistently at sunset. A basic indoor thermometer - or a smart thermostat if you already have one - will show how quickly the room temperature drops.

If the temperature falls more slowly with curtains closed, the next step is straightforward: reduce the thermostat slightly further. If the room still feels comfortable, you’ve found a direct way to cut energy use - particularly in spaces you occupy most in the evening, such as the living room or children’s bedrooms.

Why March is the ideal time to adopt the habit

The period around the start of spring is perfect for building this routine. Outdoors, it’s milder; indoors, you often only need modest heat retention to avoid running the heating at full tilt. Learn the 19:45 rule now and it tends to carry over automatically into autumn.

With longer daylight, a heating season that’s still ongoing, and moderate outdoor temperatures, a seemingly minor action becomes a genuine lever against rising energy prices. A pair of Thermovorhänge (thermal curtains) and a glance at the clock - that can be all it takes to turn stored sunshine into a real discount on your next bill.