Why You're Cold At Home At 20°C (and How To Stop Shivering Without Blowing The Bill)

So what is really going on? Why does 20°C inside never feel like 20°C outside in spring? In fact, the number on your thermostat only tells a small part of the story. The rest ? It’s physics, a little biology and a few little details that we forget.

It’s not the air temperature that matters…it’s how your skin feels

Our body does not have an ultra-precise internal thermometer capable of accurately measuring the air around us. In reality, it relies primarily on skin receptors sensitive to two main things: the rate at which we lose heat, and the temperature of the surfaces around us.

This is where there can be confusion: we sometimes think we are cold because of the air temperature, but very often it is the walls, the floor, the windows, and even the furniture that can cause us to lose heat through the principle of radiation. Indeed, the human body functions like a hot spring. When a nearby surface is colder than our body, we reflect part of our body heat back to that surface.

Let’s take an example: you are in a living room where the air is at 20°C, a seemingly comfortable temperature. However, a poorly insulated wall behind you is at 12°C, and the tiles on the floor are at 16°C. Your skin, even without directly touching these surfaces, is “aware” of their colder temperature and, by radiation, or sometimes by direct contact (if you are barefoot on the tiles for example), transfers heat to these elements. Your brain immediately interprets this rapid heat loss as a feeling of intense cold.

Average radiant temperature

To better judge the thermal sensation in a room, we must take into account the notion of average radiant temperature (MRT). This corresponds to the average temperature of everything around you: walls, floor, ceiling, furniture, windows, etc. It strongly influences thermal sensation, that is, how your body actually feels heat or cold.

Even if the air is at 20°C, a low MRT can make the atmosphere feel as if it were 17 or 18°C. Consequence: to find the same comfort, you must increase the heating to 22 or 23°C, only to compensate for the cold of nearby surfaces. Result: discomfort and a higher electricity bill.

And the humidity in all this?

We often hear that it is colder when there is humidity. This is partly true, but too dry air is also a factor.

When air is too humid, it conducts heat better than dry air. This means your skin loses heat more quickly, your clothes take longer to dry, and cold surfaces feel even colder. Result: a humid 19°C can seem freezing, while the same temperature in drier air seems quite bearable.

Conversely, very dry air does not lower the temperature, but it can create a small sensation of freshness: the moisture in the skin evaporates more quickly, and this evaporation consumes some of your heat. The effect is more moderate, but can make the atmosphere less comfortable if the room is already not very warm.

Ultimately, the ideal humidity level for good thermal comfort is generally between 40 and 55%. To measure it at home, check if your thermostat has this information. If this is not the case, a small, inexpensive hygrometer may be useful.

Drafts also have a lot to do with it

An air current of 0.2 m/s (the equivalent of a light interior breeze) can reduce the thermal sensation by 2 to 3°C. It’s huge! Where do they come from? Most often, worn window seals, poorly sealed sockets, or a poorly sealed chimney.

In less well insulated homes, cold windows also cause a form of convection which can accentuate the feeling of cold. The hot air in the room rises then cools as it passes in front of the glazing, before descending along the window like a fine fall of fresh air. This slight current, often imperceptible, can increase heat loss and reduce thermal sensation.

Little tips that can increase comfort by 2 to 3°C

Each winter, you can implement a few simple habits that can really improve comfort at home. A rug underfoot, thick curtains to cut out the cold coming from the windows at night, and reflective panels behind the radiators to reflect heat back into the room: these small adjustments are often enough to make the atmosphere warmer without touching the thermostat.

As for clothing, good socks or warm slippers, and dressing in three layers even indoors (t-shirt, thin sweater, vest) allow the body to retain heat effortlessly. With these simple actions, many people go from “I’m cold at 20°C” to “I’m fine at 19°C”, or even lower. Over a full season, this is a gain in comfort, but also several euros saved on heating.