Interior surface condensation and frosting are common complaints. Sometimes the problem is light fogging on some windows; at other times, there may be persistent and heavy frost covering the glass. Many homeowners buy new windows only to find that the problem becomes worse because the old, leaky windows actually helped to reduce humidity. The new windows seal the house more tightly, causing a rise in humidity. One solution is to reduce humidity levels in the house.

For more information on moisture and condensation, see "How your house works," and "Comprehensive air leakage control."

Alternatively, you can increase the surface temperature of the window and frame by adding another layer of glazing. New energy-efficient windows are the best solution.

When condensation forms between panes on non-sealed glazing units or storm windows, moist house air has leaked past the inner pane and condensed on the outer pane. Even dry houses can suffer from this type of condensation problem. This problem is common on second storeys where there is more air being pushed out the window because of the stack effect. The solution is to weatherstrip the inner sash to prevent air leakage; make sure that the weep holes on the storm windows, which allow water to escape, are open to the outside.

If condensation occurs inside a sealed double-glazed unit, the problem is best corrected by replacing the glazing unit. Although some specialty companies can refurbish sealed glazing units that have failed, this is considered a temporary fix that will not offer the same original energy efficiency. Check to see if the window is still under warranty.