Close your curtains at 19:45 from mid-March and save on heating costs

During the change of seasons, temperatures can vary sharply, heating bills remain expensive, and many households are looking for ways to cut costs without sacrificing much comfort. One straightforward and often overlooked habit can make homes noticeably warmer while also reducing spending.

Why checking the time becomes important from mid-March

By the middle of March, daylight hours are considerably longer. The afternoon sun sits higher in the sky, warming window areas more effectively and delivering free energy into the home. This effect can be used to advantage, provided you act at the right time.

British money-saving expert Martin Lewis has highlighted the point for years: sunset is the key moment. From around 19:45, once dusk becomes noticeable outside, people in many areas should close their curtains. Around the middle of the month, sunset in central Europe does indeed fall roughly within this timeframe.

“Anyone who consistently draws their curtains at sunset keeps the warmth gained during the day inside for longer – without needing extra heating.”

The principle is straightforward. During the day, sunlight passes through glazing and warms furniture, floors and walls, all of which retain some of that energy. Once temperatures drop outside, however, heat escapes again more quickly than many people expect – particularly through windows.

Curtains as simple insulation: household-level physics

Even double- or triple-glazed windows remain a weak point in a building’s thermal envelope. Glass conducts heat far more readily than a well-insulated wall. On cold evenings, this is immediately apparent: the panes feel cold, there can be a slight draught near the window, and the air in that area feels noticeably cooler.

This is where curtains help. They create an additional layer of air in front of the glass. That still air acts as insulation, slowing the transfer of heat between the room and the cold window surface.

• Open curtains: Warm room air flows directly along the cold glass, cools down and falls towards the floor, creating a draught.
• Closed curtains: The air immediately beside the window is largely “trapped”, so the cooling effect spreads less through the room.
• Thermal curtains: Added coatings or linings make this effect significantly stronger.

Measurements from various studies indicate that, on average, rooms with dense, heavy curtains can be up to one to two degrees warmer in the evening than comparable rooms without this “textile barrier”. That may not sound like much, but at the thermostat it can mean the difference between “heating on” and “heating stays off”.

19:45 as a guide: why this time makes sense

The precise time depends on both your location and the date. Around mid-March, 19:45 is often mentioned because sunset occurs at about this time in many places. Until then, it is worth allowing the sun to do its work.

“During the day: open curtains fully and make the most of every ray of sunshine. From sunset: close the curtains – keep the warmth in.”

A typical spring evening works like this:

• In the afternoon, sunshine comes through the window and gently warms the room.
• Towards evening, the sun disappears behind buildings or below the horizon.
• Outdoor temperatures fall and window surfaces become colder.
• Without action at this point, the stored warmth is lost more quickly than necessary.

Setting a regular time – such as 19:45 from mid-March – therefore establishes a small but effective routine. In practice, the rule is simple: as soon as it is visibly getting dark outside or the sun has just disappeared, the curtains should be closed.

Which curtains provide the best insulation

Not every piece of fabric placed in front of a window has the same effect. Both the material and the way it is hung matter greatly.

Curtains work particularly well when they:

• are woven as densely as possible;
• cover the entire window area, including the frame;
• reach to just above the floor, or even rest lightly on it;
• do not stand far away from the wall at the top, limiting air circulation behind them.

How much can realistically be saved day to day

Naturally, curtains are no replacement for professionally installed insulation. Anyone heating a home with draughty single-glazed windows will still lose energy. Yet even in modern homes with good windows, fabric in front of the glass can slightly reduce the amount of heating required.

According to energy experts, lowering the target temperature by one degree saves around six per cent on heating costs. If consistently closed curtains keep a room one degree warmer in the evening, the heating system needs to run for less time – or may not need to top up the heat at all. This is especially useful during the hours when many people are watching television or are already in bed.

At a time of high energy prices, households notice every saving. Many user reports from the UK and other countries suggest that people who consistently follow a curtain routine have kept evening temperatures stable without repeatedly turning up the thermostat.

How to make the “curtain rule” part of your routine

A small ritual helps turn a recommendation into a lasting habit. Here are several ways to make it work:

• Set a phone reminder for 19:45 – after a few days, it will usually become automatic.
• Close the curtains when you finish kitchen tasks after dinner.
• Link the routine to children’s bedtime: make “curtain time” just before the bedtime story.
• Use smart-home technology: timer plugs or electric curtain tracks can be programmed.

“The more windows a home has, the greater the effect of curtains – especially with large glazed areas and patio doors.”

Common mistakes that reduce the benefit

Small mistakes, often made unknowingly, can substantially reduce the benefit. These include:

• Completely hiding radiators behind thick curtains, which causes heat to build up only at the window.
• Leaving curtains half closed during the day, meaning free solar energy is lost.
• Buying curtains that are too short, allowing warm air to move quickly upwards along the window from below.
• Leaving windows draughty – gaps and cracks should first be improved with sealing tape.

The ideal approach is a combination of dense, long curtains, windows sealed as effectively as possible, and a sensibly adjusted thermostat. Then a moderate level of heating is often enough to maintain comfortable temperatures.

What this trick means for indoor air and mould

Closing everything up in the evening naturally raises concerns about humidity and mould. The concern is not unfounded, but proper ventilation avoids any disadvantage.

The rule is to ventilate briefly and thoroughly before closing the curtains. Airing the home once or twice for five to ten minutes allows humid air from the kitchen, bathroom and living spaces to escape. Only then should the curtains be fully drawn. Leaving windows permanently tilted open behind dense curtains, on the other hand, is a poor idea because it makes the window reveal extremely cold.

For extra reassurance, use a hygrometer. It shows the humidity level in the room. Readings between 40 and 60 per cent are generally considered comfortable and unlikely to encourage mould growth.

When thermal curtains are particularly worthwhile

Thermal curtains cost more than standard fabrics, but in certain living situations they can quickly pay for themselves. Examples include:

• older flats with ageing or only moderately insulated windows;
• top-floor flats with large glazed areas;
• ground-floor flats with patio doors and cold air from outside;
• bedrooms that are only rarely heated strongly.

Anyone who does not want to invest in new curtains immediately can improvise. Sew a second layer of fabric onto the back of existing curtains, hang fleece blankets, or use specialist thermal linings. The appearance may not be perfect, but the thermal protection will still improve.

At its heart, the idea follows one simple principle: let daylight in and keep evening cold out. Anyone who consistently closes their curtains at around 19:45 from mid-March uses that principle to best effect – and saves on heating costs without giving up comfort.