Saving energy at home? Why 19 degrees is not an ideal indoor temperature

Nineteen degrees the perfect indoor temperature? “There’s no scientific evidence for that,” he said. ‘The ideal temperature differs from person to person and from room to room.’

In recent weeks, B.’s family has been arguing about the temperature. While her teenage son is gaming in his unheated bedroom in a T-shirt, she nestles in a thick sweater under a blanket in the living room. It’s 19 degrees there all day – anything but warm, B thinks. ‘Are you sick or something?’ asks her son when he finds her like this. “It’s here to die from the heat.”

That’s not so strange. One person gets cold much faster than the other. Age, weight and gender in particular play a role in this. Women are generally more affected by cold than men. ‘That’s why it doesn’t really make sense to maintain the same temperature everywhere and at all times,’ says Wouter van Marken Lichtenbelt, professor of ecological energetics and health at Maastricht University. ‘Nevertheless, we have become increasingly accustomed to this over the past fifty years. Until energy prices went up, we thought it was quite normal for our houses and offices to be heated to 21 to 22 degrees in winter.’

Even now that we all want to save money, we continue to swear by a constant temperature. Not only in government buildings, but also in many offices and living rooms it will be 19 degrees in the coming months. That would be the ideal ambient temperature for the human body. ‘I don’t know what that is based on, but certainly not on science,’ says Van Marken Lichtenbelt. ’19 degrees is a good indoor temperature, but 17 or 18 degrees is just as good. Only there would probably be more protest against that.’

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In any case, it is not wise to heat every room of a house or office equally. It drives up heating costs and, moreover, one person will feel very comfortable with it, while the other will be too hot or too cold. ‘We can save a lot of energy by taking individual needs into account’, says Van Marken Lichtenbelt. ‘In an office garden where the temperature is not the same everywhere, employees who quickly get cold can sit in a well-heated corner. Colleagues who find 19 degrees warm, choose a cooler place. If the infrastructure doesn’t allow that, you could also install a number of workplaces with a heated desktop, for example.’

There is also no need to set the thermostat to the same level all year round. ‘Since the 1970s we have been aiming for the same temperature everywhere and in all seasons,’ says Van Marken Lichtenbelt. ‘However, research has shown that people also need much higher temperatures indoors in the summer to feel good than in the winter. So let the temperature fluctuate a little. Is it very cold outside? Then it can also be a bit cooler inside.’

Nice appetite

Setting the thermostat a few degrees lower this winter is good for the energy bill and for health. ‘If the heating is set to 21 or 22 degrees, our body doesn’t have to make much effort to keep its temperature at 37 degrees,’ says Van Marken Lichtenbelt. ‘If it’s less warm inside, the body has to work harder for that. That has a positive effect on blood flow and the functioning of the heart and blood vessels, and it also improves sugar balance.’

In a room where it is a bit cooler, we should also be able to concentrate better. But that benefit is by no means certain. According to some studies, we can indeed work or study better if the heating is lower, but there are also those that show just the opposite. For example, research from the Helsinki University of Technology shows that employees perform best at a temperature of 22 degrees. According to researchers at Cornell University, we are even most productive when it is three degrees warmer. Perhaps that also differs from person to person.

One thing is certain: just turning down the heating won’t make you lose any pounds. ‘That is often said because your heat production increases when you are cold. So you use more energy’, explains Van Marken Lichtenbelt. But unfortunately not enough to lose weight. In many cases, that energy consumption is compensated afterwards because you get an appetite for something tasty.’

Mold on the wall

However, there are also disadvantages to burning less. The indoor temperature not only has an impact on our bodies, but also on our homes and buildings. ‘The fact that it is a few degrees colder in the house does not have to be a problem in itself,’ says civil engineer-architect Jelle Laverge (UGent). ‘But in combination with other energy-saving choices, it can have harmful consequences. This also happened during the energy crisis in the 1970s. Due to ill-considered heating strategies, serious moisture problems arose in many places. Once again, the newspapers are full of tips for a lower energy bill that almost have to end badly.’

How humid the air becomes in the house depends on the moisture production and the ventilation. We are largely responsible for this moisture production ourselves. Every time we cook, wash dishes, clean, shower, make tea, sleep or even breathe, moisture is released. Now that we are more often in the living room or kitchen with the whole family because many other rooms are not heated, the moisture production there can be very high. If there is good ventilation, that is not really a problem. Only we do that less than before. To prevent heat from escaping, we no longer open the windows and buy insulation strips and trendy draft dogs to close all the cracks and crevices. ‘As a result, the moisture content in the air can increase enormously,’ says Laverge. ‘If the limit of 70 percent is exceeded for a while, you risk mold formation. At an even higher percentage you can suffer from wood rot.’

It is no coincidence that twice as many people have already died from CO poisoning compared to last year.

Jelle Laverge, Ghent University

So avoid that there is so much water vapor in the air that it will condense. From what value this happens depends on the temperature. In other words: you can prevent condensation by keeping the temperature in the room high enough. How high exactly? That is always different. Just as there is no ideal temperature for humans, there is no one for rooms either. ‘Actually, you have to check for each room in your house how much it is used, what the moisture production is, how often it is ventilated and how high the degree of insulation is. You can then choose the appropriate temperature based on that,’ says Laverge.

And what if you no longer heat a number of rooms in the house in the winter? ‘That’s not a problem in a house that is empty and where there is no moisture production,’ says Laverge. ‘But rooms in a house that are being used are better heated to 10 to 16 degrees. Even if you don’t come there often, there is always some moisture production. If a room cools down to the temperature of the outside environment, the humidity can rise very high. In a few months, such a room becomes completely moldy. Solving that is anything but easy.’

So heat your bedroom a little. Moisture also accumulates there, because people sweat in their sleep. ‘Moreover, moisture flows to the coldest places’, says Marianne Stranger, air quality expert at the Flemish Institute for Technological Research (VITO). ‘If your whole family has showered in the morning, the humidity level also rises in adjacent rooms where it is very cold. Especially now that people are less inclined to turn on the mechanical ventilation in their bathroom or open a window immediately after taking a shower to save money. That’s why it’s important to keep the temperature in the bedrooms at an acceptable level and to ventilate them for fifteen minutes every morning.’

Flower pot heaters

Air that is too humid is harmful to your health. Your airways in particular can suffer. Mold on walls, ceilings or less visible places can cause skin rashes, a runny nose, sore throat, cough and even bronchitis or an asthma attack. Those who are exposed to it for a longer period of time can suffer from fatigue, headache, muscle pain, nausea and fever.

But perhaps even more dangerous than mold growth are the alternative heat sources that some people are experimenting with at home, from fire bowls or barbecues to home-made flowerpot stoves. “Because of the fire hazard alone, it’s a very bad idea to light an open fire or burn anything indoors,” Laverge warns. ‘In addition, all kinds of harmful substances are released during combustion. This can be very dangerous, especially in combination with a lack of ventilation. It is no coincidence that twice as many people have already died from CO poisoning compared to last year.’

Our fear of letting precious warmth escape has even more damaging consequences. By ventilating less, a lot of unhealthy substances accumulate in the house. ‘They can be found in air fresheners and cleaning products, for example, or in the grill pan you use to fry a piece of meat,’ explains Stranger. ‘When you vacuum, dust is inevitably blown around and when you use a gas stove, nitrogen dioxide is released. You have to try to keep the concentrations of all those substances low. This can be done by using as few products as possible with harmful substances and by regularly ventilating well.’ It is therefore best to open the window even after cleaning. Many cleaning products contain, among other things, the fragrance limonene. If those molecules in the air come into contact with ozone, a gas that is also released by screens, eyes or airways can become irritated.

So it will be quite a balancing act in the coming months: keep it relatively warm inside, don’t let the energy bill rise even higher and make sure it all stays a bit healthy. “Enough ventilation is key,” says Stranger. ‘During the covid pandemic, we learned good habits in that area, but that is now threatening to undo the energy crisis. If we want to keep it healthy and pleasantly warm indoors, we have to learn how to dose properly. In the coming months we must therefore not air too little. But not too much either.’


– Heating one workplace more than the other

– Allow the indoor temperature to move along with the outdoor temperature

– Buy a humidity meter

– Ventilate the house for at least 15 minutes every morning and evening

– Heat rooms that are rarely used to 10 to 16 degrees

– Open the bathroom window after showering


– Heating the entire office to 19 degrees

– Completely mask off all holes and cracks

– Lower the heating to lose weight

– Keep windows and doors closed at all times

– Never heat the bedrooms

– Use a flower pot stove or fire bowl in the house