Weather is always changing, but the climate you live in will dictate what that weather will be like, so you should select the type of windows that will suit your climate best. The best windows will allow you to control the temperature within your house.

What to Look for in Climate-Friendly Windows

The first thing to look for is the correct type of window frames. Wooden frames are efficient, but tend to be costlier and need a lot of maintenance. Fiberglass and particularly vinyl windows are among the most efficient, while aluminum frames, despite their wide use in new construction, are the least efficient.

Windows will contain at least double panes, and triple pane windows are readily available and extremely efficient at keeping out the cold or heat. The vacuum created between the panes is filled with various gasses to improve insulation. The gas argon is affordable and most typically used, while krypton is used in thin specialty glass.

Know Your Coefficients

Coefficients are numerical ratings of the various aspects of a window’s glazing. They include:

• The CR rating, or condensation resistance
• The U-value, which measures thermal transmittance
• The VT, or visual transmittance
• The SHGC, or solar heat gain coefficient

Simply put, the CR will measure how much moisture is likely to collect on the inside or outside of the window, while the U-value measures the amount of heat transferred through the glass through radiation, conduction, and convection. SHGC indicates the fraction of the amount of the total solar heat that can pass through the glass. All these factors need to be taken into account when choosing the right window for the climate.

The best windows in hotter regions will be those that can block the sun’s heat from coming inside with low emissivity protection. These low-E windows are coated on the inside of the outermost pane with metallic oxide.

Metallic oxide can also be useful in colder areas, but this time the coating must be on the outer side of the innermost pane of glass, completely opposite from its hot cousin. Recommendations for other coefficients are an SHGC of 0.55, or higher on the building’s sunny side, and a U-value that is less than 0.33, or as close to 0.2 as you can find.

Mixed Climates Need a Different Combination

In mixed climates, the coefficient values you will need will depend on the side of the house and whether the area experiences longer periods of cold or hot weather through the year. In general, if the weather is colder for long periods, follow the rules for cold climates, but use a lower SHGC on the sunnier sides to help prevent heat gains that will lead to higher air conditioning bills.

Whatever your climate, experts agree that the best way to select the right window is to look for NFRC-rated windows. The National Fenestration Rating Council is a non-profit organization that provides energy efficiency ratings for windows, skylights, and doors.