Should you open or close windows in a heatwave?

Windows let the world into your workplace. They offer views, light and fresh air. But in a heatwave, all that changes. Windows can heat up a room and bring hot air inside, instead of keeping you cool. So as the summer heats up, many of us have been wondering – should you keep your windows open or closed in a heatwave?

August heatwave

Here in Berlin, as elsewhere around Europe, the heat has had the Spacebase team gasping for fresh air. Temperatures have risen to new highs: The German Weather Service (DWD) confirmed a new record just last week in Lingen, Lower Saxony, where Germany’s highest ever temperature (a sweltering 42.6° Celsius) was recorded.

Which is lovely if you’re at the beach, your toes dipped in the surf, but if you’re at work then the heatwave is a battle to stay cool. Moreso than ever now that many people are working from home rather than a large, cool, air-conditioned office with well-stocked fridge. 

Effects of working in the heat

We all know how high temperatures can make you feel sluggish and studies have shown that heat reduces our brain performance.

A 2018 paper from the Harvard T.H Chan School of Public Health found that students who lived in dormitories without air conditioning in a heat wave had lower scores in cognitive tests than others students who lived in air-conditioned dorms.

Heatwaves also affect productivity on a bigger scale. Economic output has been shown to fall during bouts of extreme heat, with one estimate suggesting that productivity falls 4% for every degree above 27° Celsius. Patterns of spending and consumption are also disrupted, with wide-ranging economic effects. Overheating carries big costs for business.

So how should you keep cool?

Your windows are one of the key ways you can regulate temperature in your workplace.

Firstly, close the curtains to keep the direct sunlight out (unless you have especially thick, dark materials as these may in fact capture the heat). Then you need to decide whether to keep the window open or closed.

The argument in favour of opening your windows is that fresh air will circulate. This prevents it from getting intolerably stuffy, as CO2 and heat build up in the room. Even better, you can open windows and doors on the otherside of the building to allow a cooling current of air to run through your room.

But others argue this is a mistake. By opening windows, you might be losing the cool air inside your shaded office, which instead is filled with hot air from outside, heated by the sun. Instead, you should keep everything closed during the daytime and only open up early morning and at night.

Open or closed?

The short answer: it depends.

Official advice can be conflicted and a survey of different sources found advantages and disadvantages for both approaches. A lot depends on the insulation of the building:

  • If your walls are well insulated, they are likely to keep the air inside cooler than the outside temperature – so you should keep windows closed.
  • If the walls are not well insulated, the outside heat will be creeping into your workspace anyway and so by opening the windows, you won’t be losing much.

As a basic principle, it’s good to open up for ventilation until the point at which it gets hotter outside than inside. Then closing your windows makes sense.

Another cool tip is to create your own air-conditioning. Freezing a bottle of water, and then standing it in front of a fan, will blow cool air towards you for some fresh relief from the heat.

COVID and heatwaves

A new factor in the discussion is COVID-19. As an EU report reminds us, “transmission of COVID-19 commonly occurs in closed indoor spaces.”

According to a professor from TU, speaking about the reopening of schools in Germany, the key to keeping classrooms safe for pupils is more effective ventilation: “Every day, at least once per hour of class as well as every break, the room has to be aired out with fully open windows and an air current set up (for example, through an open door) for a few minutes”.

If open windows is how to keep pupils at school safe, then the same principle applies for the workplace and for meeting rooms. In hot conditions, although the science of cooling might still divide opinion, opening windows for better safety. Especially if you are sharing your workspace with other people.

And if the heat of your office gets too much, you could try renting a workspace with a stunning rooftop terrace, or a boat to keep cool on the waves.