Direct Line magazine

Crack down on condensation

Updated on: 22 May 2020

Condensation forms on a window.

You may have fallen asleep in chemistry class, but condensation can’t be ignored.

Excess condensation can cause damp, which in turn can lead to structural problems and even illness.

Day-to-day activities, such as cooking, drying washing, burning fuel - even breathing! - all produce water vapour. And in the winter, when temperatures drop, cold surfaces like single-glazed windows allow this water vapour to condense back into water, which then fogs up glass and, in severe cases, can produce a seemingly never-ending flow of rivulets.

What's condensation?

Now for the chemistry lesson, but we’ll keep it brief so you don’t doze off.

To tackle condensation, first you have to understand it. It can get pretty complicated, but we’re going to keep it simple.

Condensation on a window

Air can "hold" different amounts of water vapour depending on how warm it is. This is known as relative humidity. As a rough guide, a cubic metre of air at 20°C can hold about three times as much moisture as the same volume at 5°C.

Therefore, even if it’s damp outside, the water will probably be less than in a room where people have been going about their daily lives — so open a window! If you air a room for about 15 minutes a day, you’ll get a reasonable exchange of air without cooling the house too much.

Still with us? Congratulations — you passed chemistry!

Five simple ways to reduce condensation

  • Keep lids on pans when you cook

  • Install extractor fans in the kitchen, bathroom and utility room

  • Tumble-dry clothes instead of drying them inside the house

  • Keep the bathroom/kitchen door shut as much as possible

  • Cover stone floors with carpets or rugs (make sure you have attached them securely so they don’t slip)

And some more extensive options

  • Install double glazing or secondary glazing throughout

  • Install underfloor heating

  • Insulate your external walls

  • Convert to an electric hob/oven

Did you know, you can measure relative humidity?

A hygrometer (often part of a home weather station) is very useful for keeping an eye on the relative humidity in your home. Broadly speaking, humans feel comfortable in environments with a relative humidity of about 50% at 20°C.

A hygrometer showing just under 80%

Home hygrometers aren’t always accurate, but they can give you a good idea. If you’re getting readings much higher than 50% at 20°C you definitely have a problem with the level of humidity in your home.

As well as improving ventilation, you could consider running a dehumidifier, but make sure you don’t let the humidity drop below about 30% at 20°C. Overly dry air is bad for furniture and will irritate noses and throats, as well as causing dry skin and being dangerous for asthma sufferers.

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