An estimate of the thermal performance of differing window systems can be obtained from the American Society of Heating, Refrigeration and Air-Conditioning Engineers Handbook. Condensation can form on window glazing and frames when warm air meets a colder surface. Condensation lowers a window's thermal capacity. Condensation can also result in water damage to interior surfaces and materials. Sound deadening is another important issue in window selection.
Windows are an important part of a building's sound barrier.
In general, the more airtight the window, the less noise transmitted. The type of glass and air space between panes of glass in an insulated unit also affect sound transmission. Windows are rated by sound transmission class, which is measured in decibels. It may be desirable for certain types of buildings, such as schools or hospitals or for buildings near an airport or busy highway, to use windows that have a higher resistance to sound transmission than standard windows. Long-term serviceability and maintenance requirements are important considerations for building owners who will own the property for many years.