Summary: Home window design is important. Some types home windows have lower air leakage rates than others.
When buying new windows for your new home or when remodeling it's important to consider how they open and close.
The way the window sash closes against the window frame can help improve your home's energy efficiency. The sash is the wood, vinyl, or metal frame around the glass.
There are basically six traditional operating window sashes to consider. I have them listed below in the order of increasing air leakage.
Image Courtesy of the U.S. Department of Energy
· Awning Widows
Because the window sash closes firmly against the frame, awing widows generally have lower air leakage rates than sliding windows. The sash is hinged at the top and can open outward or inward.
· Casement Widows
Casement windows also have low air leakage because the sash closes by being mechanically cranked in against the frame.The sash can be hinged on either side.
· Fixed Glass or Fixed Glass Window
Fixed panes don't open. They are airtight and they provide no ventilation.
· Hopper Widows
A Hopper window is an awning window hinged at the bottom.
· Single and Double Hung windows
Since the sash has to be able to slide vertically in a double-hung window, there is more of an opportunity for air leaks. Both the upper and lower sash operate with a double hung window, while just the lower sash operates with a single hung window.
· Single and Double Sliding Widows
These widows are like miniature sliding glass patio doors with either one sash or both operable.
It should also be noted that window sashes that open outward prevent the use of exterior storm windows. Interior storm windows would have to be used for outward opening windows.
Be sure to read my page on Which Window is Best.