By Jim Dulley -
Style and type top priority for energy efficiency
What are the most important features to look for when shopping for windows?
It can be extremely difficult to sort through all the marketing hype from salespeople to make the proper replacement window decision. Without telling salespeople who I was, I sat through many sales presentations at my mother’s house. I was appalled at some of the
It’s important to note that because windows are an expensive project, energy efficiency should not be your only reason to purchase new ones. Other efforts will save more money, and you can find ways to make your existing windows more energy efficient. But if you truly need new windows, there are some considerations.
The proper selection not only depends on the characteristic of the window, but also on your specific house and family lifestyle. What is best for your next-door neighbor’s house may not necessarily be best for yours. For example, you may want a view of a particular area outdoors or want springtime ventilation whereas your neighbor may keep their blinds closed and air-condition continuously.
You have mentioned the three main decision criteria for selecting replacement windows: frame material, style of window, and glass type. From the standpoint of energy efficiency, the glass type and style of window are more important than the frame material, which has a greater affect on the functionality, durability, maintenance and appearance.
The four most common frame materials for residential windows are vinyl, fiberglass, wood and clad wood, and each has its own advantages. Vinyl is energy efficient and virtually maintenance free. They also are made to the precise dimensions of the window opening instead of having to shim out standard sizes.
In order to attain adequate rigidity, the vinyl frame extrusions have many webs and chambers inside. These chambers create natural insulation, plus the vinyl material itself is a poor conductor of heat. For greater R-value, several vinyl window manufacturers inject expanding foam insulation inside the chambers as the frame is assembled.
Always look for sash frames that have welded corners for strength. Because the outer window frame is screwed rigidly into the window opening framing, welded corners in it are not as important as with the sash frames. If you select vinyl frames for large windows, especially in hot climates, they should have steel reinforcement internally. When vinyl gets hot in the sun, it loses strength and rigidity.
Fiberglass frames are extremely strong and can be painted any color to match interior or exterior house colors. Because its primary component is glass, fiberglass frames expand and contract with temperature changes about the same rate as the glass panes to minimize stress.
This characteristic is an advantage for dark frame colors exposed to the sun, which can create a substantial temperature range throughout the day and night. The strength of fiberglass frames is also an advantage for smaller windows because narrower frame cross-sections are acceptable. With other frame materials, a thicker frame can reduce the glass area too much.
Wood window frames have been around forever, and when properly maintained, have a very long life. Wood frames are also the most attractive. This is true even if you choose to paint the frames. It’s easier to cut more complex and sharp detail into wood frame surfaces. The drawback of wood is some regular maintenance is required for appearance and energy efficiency.
Exterior vinyl- or aluminum-clad wood frames greatly reduce the maintenance requirements. The natural wood can still be exposed on the indoor surface so they look like wood windows from indoors. Some vinyl and fiberglass frames are available with natural wood indoor cladding to provide the appearance of real wood frames.
The proper style of window depends primarily on the appearance and features you desire more than the energy efficiency characteristics. For example, people often select double-hung windows because they can be tilted in for easy cleaning from indoors. Windows that close on a compression seal, such as casement and awning windows, tend to provide the best long-term airtight seal. Also, casement windows can catch breezes and direct them into the house for natural ventilation.
Because glass is most of the window, the type you choose is the key to its energy efficiency. Double pane-glass with low-E (low-emissivity) coatings and inert gas in the gap between the panes is adequate for most climates. Triple-pane glass may make sense for severely cold climates.
The location of the low-E coating on the various pane surfaces, often more than one, affects whether the glass is better for winter or summer savings. You may end up selecting different glass options for different windows in your house.