Why does condensation form on my windows in the winter?

This depends on the types of windows installed and the relative humidity levels in the home.

1. The condensation is forming on the room side of the glass.

This is caused by a combination of high interior air humidity and a large temperature difference between the window and the indoor air. When warm interior air hits the cold window, it decreases in temperature. Cold air cannot hold as much moisture as warm air, which is why the condensation forms. If the condensation forms in large quantities and runs down the glass, the windowsill or underlying wall materials may become moldy or moisture damaged, and could require repairs.

Remedies for reducing the formation of condensation include:

•  Lowering the humidity (removing plants, hanging laundry, storing wood outside to dry, installing an exhaust fan, etc.)

•  Installing heat sources below windows to reduce the formation of condensation by flowing warm air across the glass.

•  Installing storm windows on single-pane windows, and keeping blinds or curtains slightly away from the windows to allow airflow in front of the windows.

2. The window installed is doubleglazed (two panes of glass separated by a sealed spacer), or triple-glazed (three panes of glass separated by sealed spacers), which is also known as a thermopane window.

The seals between the panes have deteriorated, which allows condensation to form between the panes of glass. Although it cannot be cleaned and is often considered inconvenient to look through, this diminishes the insulating capacity of the window only slightly. However, it is often considered inconvenient to look through. Correction of the problem typically involves having the window replaced.

3. The following are some of the main features that are available in new energy-efficient windows:

• Double or triple-glazed glass (i.e. thermopiles). These are two or three panes of glass manufactured as one window with a very thin separation between the panes. This separation width provides less convective heat loss than the typical separation width of 2-4 inches, which is often observed on standard thermopane or singlepane windows equipped with a storm window.

• Low-E coatings. Installing heat sources below windows to reduce the formation of condensation by flowing warm air across the glass.

• Inert gas fills. Another big advancement in window technology has been the introduction of inert gas fills into the space between the glazings. Argon and krypton are the usual choices, with argon being the most common. Filling the space between the glazing with these heavier gases reduces heat loss due to convection and conduction.

• Low-conductivity spacers. The spacer between the glazing at the perimeter of the window has historically been made out of aluminium, which is not only lightweight and durable, but also provides considerable heat loss. Newer non-metallic spacers are now available to reduce heat loss at this location.

The cost for the inclusion of the energy efficiency features described above varies, but can be 10-15 percent more than standard double-glazed units. However, many window manufacturers are converting their production lines to produce only high-performance units. Some super high-performance windows that are using cutting-edge technology for even more energy savings than those described above are available, but at considerably higher costs.

Proper installation is especially important with high-performance windows because poor installation techniques can negate their performance. Installation should be completed in accordance with manufacturer’s recommendations and should reflect current industry standards. Be sure to check out your contractor’s qualifications to ensure proper installation.

Completion of an energy efficiency assessment is recommended prior to upgrading in order to determine the feasibility of upgrading windows.

Contact AmeriSpec Inspection Services to learn more.

This article appeared as a newsletter from AmeriSpec Inspection Services in December of 2015.