Window Condensation – Where the Water Vapour come from?

Acknowledging and managing the sources of water vapour inside a house can assist to decrease the probability of condensation forming on windows and doors.

Water Vapour and Condensation

Condensation occurs when a gas or vapour modifications to a liquid. In the house, this occurs when water vapour condenses onto surfaces such as windows, doors and mirrors.

When air filled with water vapour meets a surface area– such as a window pane– which is cooler than itself, it will shed surplus water vapour on that surface area, initially as a great mist or, if in fantastic enough amounts, as beads of water.

One method to lower the amount of condensation that occurs in the house is to offer adequate ventilation for wet air. Another is to make efforts– where practicable– to reduce the formation of water vapour in the first place.

Sources of water vapour inside a home


  • Two sleeping adults produce around one litre of wetness in 8 hours.


  • Steam clouds from heating water in saucepans and kettles. The gas in a cooker contains some water and average gas cooker can produce approximately one litre of moisture per hour.

Washing up

  • Through vapour clouds, released by the warm water.

Bathing, laundry, and damp outer clothing

  • These prevail major sources of water vapour in the house.

Heating systems

  • A flueless gas heating system can produce up to 350cc of wetness per hour.

Indoor plants

  • The life processes of plants are a substantial source of water vapour.

New homes

  • The bricks, lumber, concrete and other materials in an average 3 bedroomed house soak up about 7,000 litres of water during building and construction. Much of this is dissipated inside later throughout the drying out duration.

Sources of water vapour outside a house

Water vapour is always present in the outside air and levels depend on atmospheric conditions (temperature level and humidity).

A case in point is the formation of condensation on the whole surface area of a car, including the glazing, when left in an exposed location. This condensation would generally be gotten rid of using both the wipers blades and a squeegee.

As double and triple glazing becomes more efficient, heat is less able to pass through the window and warm the outer pane. This suggests that the external pane surface area remains cold producing the conditions that may permit condensation to form.

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