Understanding Condensation

A guide to answering questions regarding condensation, indoor humidity and exterior condensation.

How to Understand Condensation and Windows

12 May 2017

 What causes condensation?

Condensation on windows and other cool surfaces in the home can both be annoying and possibly injurious to your home. Because the most often visible condensation is seen on windows, it’s easy to blame condensation as being a window fault.This is not true in most cases. Any cool surface will cause excess humidity to condense on it.

If there is condensation on windows, you may be assured there is condensation on walls. This is more serious since that can penetrate the walls and cause internal problems. The cause of condensation is air saturated with too much humidity or water. When this happens, air cannot hold the excess humidity. It gets rid of it by condensing it on the most convenient cool surface.

Understanding Condensation Diagram


How can I reduce condensation in my home?

The obvious answer is to reduce the humidity and decrease the number of cool surfaces in your home. Your first step is to find what the humidity level in your home is. This will need to be monitored regularly as the temperature outside varies. Devices that measure humidity are called hygrometers. You can buy one at most reliable hardware and home centre stores.

Here are a few things you can do to control humidity:

  • Make sure your humidifier is working correctly. Turn it down as the weather becomes colder.
  • Vent all appliances and vents to the outside.
  • Vent attic and crawl spaces.
  • Cover the earth in your crawl space
  • Make sure your humidifier is working correctly. Turn it down as the weather becomes colder.
  • If you have a forced air furnace, make sure your home is properly ventilated by installing a fresh intake.
  • Clothes dryer vented into the living space.
  • Don’t store firewood inside
  • As a temporary solution, you may want to try opening your windows a little each day to allow the exchange of colder drier air with warmer more humid air. This should not affect your energy bill in any substantial manner.
  • Install energy efficient windows.

What is an energy efficient window and why will it help?

Windows, doors, and skylights have become an important part of the energy savings plan. They don’t allow cold air to enter around a window, thus cooling the surface. Spacers between glazing in double or triple glazed windows are more energy efficient and do not allow cold air to migrate through them causing the glazing to cool.

Special metallic coatings have been developed (known as LowE or low emissivity) which reflects radiant heat and restricts its flow through glass. During cold weather, it will keep heat inside. In hot weather, it keeps heat outside.

low e II diagram

Using energy efficient windows will keep the interior glass surfaces warmer and thus reduce the interior cool surfaces on which moisture can condense.

Summary to reduce condensation:

  1. Reduce the amount of moisture in the air as the outside temperature gets colder.
  2. Make sure your home is properly ventilated.
  3. Use exhaust fans.
  4. Use vapour barriers on the earth in your crawl space.
  5. Use a hygrometer to measure and regulate your humidity level.
  6. Use energy efficient windows (Installing a storm window in an older home may help.)
  7. If building a new home, make sure your builder is using only kiln-dried lumber and make sure he places heat vents beneath patio doors.

Remember, there’s always a possibility that in very cold, unusual circumstances, you may still have some temporary condensation. But if the humidity level is proper and the home correctly vented, this will be short lived.

Always Choose Certified Windows

Marvin windows and doors are certified and have undergone rigorous structural, air, and water infiltration testing and energy efficiency evaluation.

Certified Windows


Do you want to learn more about condensation, its causes and cures? We’ve created this guide to help you along the way:



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