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Condensation

Condensation is the dampness formed when air laden with water vapour is cooled by contact with a cold surface.  Here you can find out how to identify and treat condensation.

  • Why do you get condensation?
  • When is it a problem?
  • How can you tell it’s condensation?
  • What can you do about it?
  • Heat recovery fans
  • Dealing with mould growth
 

Why do you get condensation?

The air we breathe can hold varying amounts of water vapour, depending on its temperature. If warm moist air is cooled by a cold surface, such as a window or external wall, it is then no longer able to hold the same amount of water vapour. The air-borne moisture turns into droplets of water and collects on the cold surface. This is called condensation.

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When is it a problem?

Every home gets condensation at some time – usually when lots of moisture and steam are being produced – for example, at bath times, when a main meal is being cooked or when clothes are being washed.

It is quite normal to find your bedroom windows misted up in the morning after a cold night. There is nothing much you can do to stop this.

However, if your home never seems to be free from condensation, read on.

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How can you tell it’s condensation?

Are you sure it is condensation? Dampness in your home may not be caused by condensation at all. It could be caused by leaking pipes, a leaking roof or rising damp.

Leaks often result in patches of damp coming through the plaster and wallpaper near where the leak is. Rising damp can be identified by a damp 'tidemark' low down on the walls indoors.

Condensation, on the other hand, is surface dampness. It mainly occurs on cold walls indoors and other cold surfaces such as tiles and cold water supply pipes under sinks and hand basins.

Condensation is usually at its worst during the winter. It often results in black mould growing on walls and other surfaces.

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What can you do about it?

The four main ways to deal with condensation are:
1) Produce less water vapour or steam in your home.
2) Don't let the water vapour and steam that is produced spread all round the house.
3) Keep your home ventilated
4) Keep your home warm.
To deal with a condensation problem effectively, you will probably need to do all four, though the first three are the most important and can be done at no cost.
 
1) Produce less water vapour

The amount of condensation depends on how much water vapour is in the air.

Many everyday activities add to the water vapour level in your home, but their effect can be kept to a minimum.

Cooking
  • Cover pans when you’re cooking.
  • Don't leave kettles and pans boiling longer than necessary.

Drying clothes
  • Hang washing outside to dry whenever you can.
  • If you have to use a tumble dryer make sure it's vented to the outside.
  • If you have to dry washing indoors use the bathroom and keep the door shut and the room well ventilated.
Do not hang wet washing on radiators all round your home – doing so is very likely to cause condensation problems.

Bathing
Keep the bathroom door shut and the room well ventilated.

Paraffin and some types of gas heaters
  • Avoid using these sorts of heaters - they are one of the main causes of major condensation problems.
  • Paraffin heaters, portable bottled gas heaters and fixed flueless gas heaters all produce heat, but at the same time they also put a lot of water vapour into the air.
  • One gallon of water is produced by one gallon of gas or paraffin burning. Paraffin and portable bottled gas heaters can also be dangerous and very expensive to run. They can cost as much as, or even more than, heating using peak rate electricity.
 
2) Don't let it spread

  • Confine wet air to just a few rooms
  • Your bathroom and kitchen are 'wet rooms' - keep these doors shut so the wet air can't spread to the rest of your home.
  • Keep the door shut to stop the moist air spreading into the rest of your home, especially when you're washing, cooking or taking a shower or bath,
  • At the same time make sure your bathroom and kitchen are well ventilated so the water vapour can escape outside.
  • This is even more important if some of the other rooms are very cold. If rooms are not being used and are unheated it's a good idea to keep their doors shut.
  • Don't completely draught-proof kitchens, bathrooms and other rooms where condensation is already a problem - you could make it far worse.
 
3) Keep your home ventilated

  • Let wet air out
  • The best way to remove water vapour is by providing adequate ventilation. Nobody likes draughts, but some ventilation is vital.
  • Keep a small window ajar, or a trickle ventilator open, in each occupied room to give background ventilation, (but make sure your home is still secure).
  • Open the windows to let the water vapour out, especially when you're doing the washing or cooking.
  • Windows near the ceiling are more effective at letting water vapour out than ones lower down.
  • Heat recovery fans are very good for ventilating 'wet rooms' such as bathrooms and kitchens. They are more effective than ordinary fans, since they get rid of the moisture from the air and let fresh air in, and also recycle the heat back into your home.

But don’t forget to keep your home secure!

  • If you open windows, make sure you shut them again when you go out.
  • If you leave small windows open for background ventilation, make sure they're not accessible from the outside, for example, from a garage or shed roof.
  • Leaflets on home security are available from the city council's Community Safety Team - contact them on 0116 252 6005.
 
4) Keep your home warm

  • Heating your home can help solve a condensation problem, but only if it’s used in addition to the other three steps already described.
  • However, first of all it needs to be ‘dry heat’, such as central heating or gas fires, not paraffin or portable gas heaters.
  • Secondly, simply heating your home will tend to warm the air. Warmer air holds more water vapour, so the air in your home could become even wetter. There’ll be more water to condense out onto any cold surfaces.
  • This is more likely to be a problem if you only put the heating on for an hour in the morning and an hour at night. In this case only the air is warmed, and building fabric itself stays cold, so there’s more chance of warm wet air being in contact with cold surfaces.
  • The best approach to heating in order to reduce condensation, assuming you have taken the other three steps, is to heat your home at a low level for a long time.

Keep the heating on, but set it to provide just a minimum of background heating. This will warm the whole building up and keep it warm, so there are no cold surfaces.

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Heat recovery fans

Heat recovery fans are expensive, but can be a very good investment. They cost about £250 to buy and install.

Heat recovery fans are very effective since they:
  • get rid of the moisture (and smells) in the air, especially from kitchens and bathrooms
  • recycle the heat at the same time
  • bring fresh, filtered air into your home
  • improve the health of your home.
Heat recovery fans are designed to be left running continuously on a low speed setting.

De-humidifiers

Installing a de-humidifier may not be the best way of tackling condensation. They are expensive to buy (£200 to £300) and must be emptied every day. However, they are useful for drying damp buildings out, for example after leak damage, or for specific rooms.

De-humidifiers are no substitute for the vital, no-cost measures of reducing the amount of water vapour put into the air and keeping rooms well ventilated.

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Dealing with mould growth

The best way of tackling mould is to reduce the condensation levels and prevent it growing in the first place.

Dampness from condensation often causes the growth of black mould on walls and other cold surfaces such as tiles. Mould and mildew can also grow on furnishings, curtains and even clothes in wardrobes. It may first appear in corners or behind cupboards, but it can spread across entire walls.

Mould can spoil wallpaper and furnishings and can make your home unhealthy.

Mould on washable surfaces can be removed by wiping down with detergents or proprietary mould removers. It can be washed out of fabrics, but may leave stains or spoil colours.

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