Window Treatments for Energy Efficiency
Windows transmit energy in two ways: ‘Leaky’ windows allow air drafts (convective heat transfer); while all windows allow radiation heat transfer. Dual panes and ‘low-E’ glass reduce radiation heat transfer. Low-E is low emissivity, and is principally a concern where windows are the cause of heat gain, as in desert climates. Dual panes help prevent warm objects inside a home (including bodies) from radiating heat to cold window surfaces.
There are a number of approaches to re-mediating windows. A combination of approaches may be used in a given home.
Repair
First, repair windows that do not close properly. Often there is an accumulation of old paint that prevents closure. Sometimes other repairs are required in order to get the windows to close completely.
Weatherize
Apply weather-strip and ‘rope’ caulk to windows that you wish to be able to open and close.
Use ‘shrink film’
For fixed windows (those that are not designed to open), apply ‘shrink film’ to the inside window frames where appropriate and feasible. This is an easy and low cost solution and the film can remain in place for years on windows that are out of the way. The film can also be used seasonally and re-applied.
Seal
Most home-owners have operable windows (those that can be opened) that are never actually opened. These can be sealed on the outside with butyl or elastomeric (not silicon) caulk to stop air leaks. Shink film can be applied to the interior frame to reduce radiation loss and further air seal.
Storm windows
Exterior storm windows are a great option where you want to retain the original look of double-hung windows and still be able to open the windows. They can also be used outside of decorative fixed windows. Properly sized and installed storm windows in combination with existing single pane windows perform as well as dual pane windows. Good quality aluminum storm windows outlast vinyl and wood dual pane windows and are less expensive. They can be custom sized to match existing windows. And storm windows can be ordered with low-E glass to cut down on heat gain. Exterior storm windows cannot be used in combination with existing windows that swing outward. Interior storm windows are an option, but the look may be unsatisfactory for some home-owners.
Retrofit with new dual pane
Replacing existing single pane windows with dual pane windows is a great way to go, but is the most expensive. Vinyl performs well. Wood looks better but is more expensive than vinyl. And wood might not perform as well as vinyl, since wood is a better conductor of heat than vinyl.