Anti-Cold Trick: Use Daylight, Thermal Mass and Thermal Curtains Without Heating

On cold days, it is tempting to turn up the thermostat and hope the bill will not hurt too much at the end of the month. But what if there were another way? This simple trick makes use of daylight, thermal mass and dense fabrics to make your home feel noticeably warmer, without heating. It works not only in the milder months but on dull winter days too. It may sound a little like a DIY project, yet it delivers a quiet boost in comfort.

Indoors, there is silence: no clanking radiator and no hum from a fan. Sitting on the rug, I look towards the south-facing side, where the glass has turned a pale gold. Dark water containers stand in front of the window, lined up neatly like small guards. A thick curtain hangs beside them, still open. Once dusk arrives, I will draw it, as though asking the warmth to stay indoors. We all know the point when cold gradually creeps through a flat, and a single movement changes the feeling entirely. The thermometer falls in the evening, but the room does not cool as quickly. It is an unassuming trick with a surprisingly effective result, and it changes the way a winter day feels. That is the point.

Why this anti-cold trick works at all

The principle is almost obvious: let solar warmth in while it is available, then reduce heat loss as much as possible afterwards. During the day, a window acts like a small greenhouse surface. Dark materials such as water, stone and ceramic absorb radiation and retain it. The more slowly a material responds to temperature changes, the longer it holds on to that heat. Then comes the second stage: thermal curtains and seals slow down the loss. The difference is noticeable not as a blast of heat, but as a persistent mildness. There is no magic involved, simply a clever combination of light, material and timing.

One example comes from a period kitchen in Leipzig, with south-facing windows, high ceilings and draughty gaps. During winter, five 10-litre containers, painted dark, stood on a simple wooden bench directly in front of the window. The curtain remained open during the day so that sunlight could reach the containers. At around 16:00, the heavy curtain was drawn and a draught excluder reduced the airflow beneath the door. Over one week, the room’s average evening temperature was 1.5 to 2.5 degrees higher than in previous years, without heating. It was not sauna-like. However, the living space did not cool immediately while the water quietly released its residual warmth. You could sit at the table longer without a coat on. That is exactly what matters.

The physics is straightforward. Water has a high heat capacity, so it moderates temperature fluctuations. A 100-litre store warmed by 5 to 8 degrees during the day holds roughly 0.6 to 0.9 kWh. That will not last a whole night, but it provides a meaningful buffer during the colder hours. Glass lets short-wave radiation pass through readily; the dark store absorbs it, and the energy later moves into the room air as heat. Since curtains, sealing tape and a tightly closed evening setup reduce losses through windows and gaps, the small store lasts longer. Store heat and keep cold out – that is all it takes to shift the curve.

How to use the anti-cold trick step by step

During the day, clear anything that could block the sun. Place 50 to 150 litres of water in dark containers or glass demijohns directly in front of south- or west-facing windows. A shelf, bench or even bricks used as a base can help. Pull pale curtains aside and keep the windows clean. In the evening, close thick thermal curtains, fit draught excluders to door gaps and apply adhesive seals around frames. If you wish, attach a layer of transparent bubble wrap to the inside of the glass – removable, inexpensive and noticeably effective. Open everything again in the morning, and briefly air the room to let moisture out. The routine takes only minutes and works like a discreet heat buffer that you recharge every day.

The potential mistakes are remarkably human. A curtain sealed too tightly to the floor can trap humidity in the window gap, so leave a few centimetres of clearance or air the room occasionally. Do not press water containers directly against the frame, as condensation can drip where there is no air circulation. Avoid cramming the area full: the sunlight needs some space to reach the surfaces. And, honestly, nobody will do this perfectly every day. Set fixed prompts instead – curtains open in the morning and closed at night – just like brushing your teeth. A small routine can have a big effect. When it becomes very cold, add rugs and create an internal “airlock” in the hallway: a curtain that separates the cold from the stairwell.

You do not need a workshop, only a willingness to try a simple everyday hack. Sometimes it feels like a small victory when the room stays warmer in the evening although nothing is humming.

“We tried the containers in November. The difference may be only two degrees – but those two degrees decide whether you put on a coat or spend the evening relaxed at the table.” - Karin, 58, rented flat

• 10–20-litre water containers, dark or covered in a dark material
• Thermal curtain (heavy, close to the floor and guided tightly at the sides)
• Self-adhesive sealing strips for windows and doors
• Draught excluder for the door to a cold hallway
• Optional: bubble wrap for the window and a hygrometer to monitor moisture

What is realistic, and where are the limits?

Do not expect summer conditions. This trick is most effective during the milder months and on sunny winter days, while on overcast days it slows the rate at which the room cools. In a 20–25 m² room with 1.5–2 m² of south-facing window, an extra 1–3 degrees in the evening is possible, sometimes more. That may sound modest, but it feels significant. Across several weeks, it reduces the need to switch on the heating, saving money and frustration. During a prolonged freezing spell, you will need additional measures: rugs for cold floors, closed internal doors and perhaps a small, efficient spot heater for times when you are seated. The key remains the same: let warmth in during the day, then seal up at night. And yes, it can be almost enjoyable to watch a room hold on to its warmth.

Key point	Detail	Benefit for the reader
Solar trap at the window	Dark thermal mass (water, stone) directly behind glass	Use free radiation rather than electricity or gas
Sealed evening routine	Close the thermal curtain; reduce gaps with sealing tape and draught excluders	Significantly reduce heat loss so the room cools more slowly
Moisture management	Air briefly, leave space from the glass and use a hygrometer	Comfort without mould risk, with clear-headed rather than stuffy air

FAQ

• Does this work without south- or west-facing windows? Yes, although the gain will be smaller. With north-facing windows, focus more strongly on sealing and curtains. Make use of every minute of diffuse light and add more mass.
• Can it cause mould? The risk rises if moisture becomes trapped. Leave a little gap between the curtain and the glass, air the room briefly and thoroughly, and check with a hygrometer. That keeps things manageable.
• Which containers are suitable? Food-safe 10–20-litre containers or glass demijohns. Paint them dark or cover them with fabric so that they absorb radiation effectively. Position them securely so that they cannot tip over.
• How much can you really save? It varies. Test households recorded 5–15 per cent fewer heating start-ups during the milder months. The aim is noticeable comfort alongside smaller, recurring savings.
• Does bubble wrap on windows help? Yes, as temporary internal insulation. It is a simple option for older single glazing: less heat loss and a more comfortable radiant feel in the room.

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