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How to Prevent Condensation on Windows

The GGF has provided some of the information on how to prevent condensation in this article. You can download the full leaflet for free.

What is Condensation?

Condensation happens when water vapour in the air turns into liquid. This liquid appears on windows or cooler surfaces.

Our homes always have water vapour in the air. It comes from things like steam from boiling water. The vapour quickly becomes invisible as it mixes with the air.

Warmer air can hold more water vapour. But there is a limit. When the air reaches that limit, we say it is ‘saturated’. Saturated air cools when it touches a colder surface. This releases its extra water vapour onto that surface. At first, it looks like mist, but if there is enough of it, it becomes moisture. We call this condensation.

Condensation occurs on windows and doors when the inside of your home is warmer than the outside.

There are two conditions for condensation to form in your home:

  • The window glass surface is cold.
  • There is a lot of water vapour in the air.

Condensation on the outside of the windows means they are doing their job. The outside pane of glass doesn’t get warmed by heat escaping through the glass, so it stays cooler than the inside. This causes the condensation.

When does condensation become a problem?

If you see condensation between the glass panels of your window, it means your window seals have blown. It may look cloudy or misted and needs to be replaced. You may feel a noticeable draught and your energy bills may increase.

The current Building Regulations, called Approved Document L: Conservation of Fuel and Power, say that new or replacement windows must meet certain standards. To meet these standards, we must install energy efficient windows and doors.

To help save you money on heating, we install A-rated windows as standard. You can upgrade to A+ for even better performance against condensation. These windows capture heat from the sun and prevent heat loss, keeping your room warm.

We offer a 15-year guarantee on the sealed unit. If your window forms condensation between the glass, we will replace it for free. Please call us or request a service visit if you are experiencing this issue.

How double or triple glazing helps prevent condensation

If you heat a room, the inner glass of a double or triple glazed window will be warmer than if it had single glazing. This makes it less likely for condensation to form when warm, moist air in the room touches the inner glass.

Although double and triple glazing can help reduce condensation, it does not control the amount of water vapour in the air. Windows act as insulation, designed to prevent heat loss from outside your home.

Condensation can occur in a room that is not regularly heated for cost-saving reasons. In these cases, the inner glass of the window becomes almost as cold as the outside temperature. Cold air can hold less water vapour, resulting in condensation.

Windows in these rooms are typically kept closed. But if water vapour is generated elsewhere in the house, it will find its way into the room and not be able to escape.

Modern homes are designed to block draughts, reducing natural ventilation. This design feature may lead to increased condensation in modern homes. If your home has cavity wall insulation, loft insulation, double or triple glazing, and draught-proofing, it’s more likely to trap moisture.

In most cases, condensation is a result of poor ventilation. In older buildings, condensation is more likely caused by indoor temperature.

To combat this issue, here are some tips for reducing condensation:

  • Improve natural ventilation in the room by adding an extractor fan, an airbrick, or ensuring that the window trickle vents are open.
  • Open at least one window in each room for a period of time each day to allow for air circulation.
  • Install or clean kitchen and bathroom extractor fans and direct the steam outside.
  • Close bathroom and kitchen doors. It may also help to draught-proof internal doors to prevent the transfer of air with high water vapour from these rooms.
  • Dry clothes outdoors whenever possible.
  • Increase the air temperature in the house.
  • Make sure all radiators are placed under windows to maintain the temperature of the inner glass.
  • Use a portable dehumidifier.

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