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Should you open windows in winter?

Posted by Alex Barrett on 7 November 2016 at 11:15 am

When it comes to energy saving the less heat your house loses the better. One of the best ways to accomplish this is by draught proofing. By stopping warm air from leaking out of your house you prevent heat loss and so reduce the amount of energy you have to use for heating. This suggests that for a perfectly energy efficient house you should avoid opening windows unless you absolutely have to.

However indoor air quality is important as well. Indoor air can easily become stale, and strong smells from cooking and chemical cleaners need to be dispersed. So should you open windows in order to let in some fresh air? Or is it best to keep your house as airtight as possible?

The answer is that it depends. A perfectly energy efficient house would be completely airtight, with no draughts or leaks. This is one of the principles behind the Passivhaus [1] standard where heat loss is reduced to such an extent that very little heating is needed. In an airtight house you need mechanical ventilation to keep the air fresh. This can be combined with a heat recovery system (MVHR) which keeps as much heat as possible inside the building. In such a house it is inefficient to open windows in winter, as it would undo all of the good work done by the heat recovery system.

However most buildings aren’t built to such a high standard. Older houses were built at a time when insulation and energy efficiency weren’t a concern. They were designed to have a leaky envelope so that the house would “breathe”. Opening windows for a few minutes (or leaving extractor fans on longer) might be the answer to remove stale air in winter in an older home. One good trick for airing the house is simply to open windows or doors at opposite ends of the living space to create a through draft for a few minutes. If you do this before you lock up and leave for work you should come back to a fresh home. If your heating is programmed to come on a little before you arrive home if will also be a nice warm home.

Energy losses build up when doors or windows are left open for extended periods. This is particularly a problem in commercial buildings. Many shops leave their doors open throughout the winter, in order to attract customers. This loses a vast amount of heat, as the temperature inside the shop must be maintained the entire time. It has been estimated that leaving a shop door open can emit 91 kg of CO2 per week. The Close the Door campaign [2, 3] has been set up to promote door closing, both to save on energy for space heating and to improve the air quality inside shops, many of which are likely to be located on busy streets with a lot of traffic fumes in the air.

In conclusion, most people will want to use their windows for ventilation, even in the depths of winter for a short time. The best way for most people to cut down on ventilation heat loss is to use extractor fans (ideally with heat recovery) and make sure that your draught proofing is up to standard. Make sure that a window isn’t leaking air when it is closed. That way you will be in control of whether you are allowing heat to escape or not. Constant heat loss through leaks around windows can quickly add up to far more wasted energy than opening a window from time to time to clear a room of stale moist air.


  1. Passivhaus Institute
  2. The Guardian
  3. Close the Door

Image Credit: WashtheBowl via flickr

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1 comments - read them below or add one


allenspComment left on: 30 November 2016 at 6:52 pm

No mention of trickle vents I note! Open or not?

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