Choosing windows for cold, mixed and hot climates

USA and Canada are usually roughly divided into four climate zones, while Australia is divided in eight (1- High humid summer, warm winter; 2- Warm humid summer, mild winter; 3- Hot dry summer, warm winter; 4- Warm temperate; 5- Mild temperate; 6- Cool temperate; 7- Alpine…).

You should inform yourself on the exact type of climate on your region and on the windows that better respond to it.

Broadly we can consider three main climate situations in terms of windows and their different SHGCs (Solar Heat Gains Coefficient) and U-values (insulation value).

1) Cold climate zones;
2) Mixed climate zones; and
3) Hot climate zones…

While countries like the USA, or Australia have all these distinct climate zones, others like Canada or UK have basically one type of climate zone.

See also: Best windows rating

Windows for Cold climates

Most of North-America and UK have Northern cold climates, which means that homeowners are primarily interested in heating.

To get that heating, the windows should have a low U-factor, that is, the windows should have a high insulation-value to keep the heat indoors. Windows need to have a U-factor as low as possible (less than 0,3).

As to the Solar Heat Gains Coefficient (SHGC), it should be high or relatively high by obvious reasons: heat gains are beneficial.

Unless you have significant air conditioning costs, the SHGC coefficient should be high, often in the 0.40-0.60 range. Only windows located in parts of the house where they can get unwanted heat gains should have a lower SHGC.

Besides choosing windows with low U-values and high or relatively high SHGC, also locate the majority of them to the south (or north, in the southern hemisphere) to get the winter sun.

Windows for Hot climates

Climates like those of Florida in USA, or those of Northern Australia are typically hot climates, that is, climates where overheating is the main concern and where the windows are basically designed to avoid the heat to enter into the house.

To achieve that goal you should install windows with a very low SHGC (Solar Heat Gain Coefficient): 0,2 or less, if possible.

As for the insulation-value of the window (its U-value), that’s a more controversial issue...

If your home is air-conditioned, bet on windows with low U-value. It's a guarantee that the air conditioning will not be lost to the outside.

Obviously, windows with a low U-value are not important in hot climates where air conditioning is scarcely used (the case of some tropical climates, where cooling is based on natural ventilation or shading strategies).

In hot climates also prefer windows with light colored frames and with designs that provide large ventilation (casement windows, for example). Also locate them on opposite sides of the house to allow cross ventilation, and do not forget overhangs, awnings and other ways of getting shade…

Windows for Mixed climates

Many temperate (and less temperate climates) are mixed climates in the sense that they require both heating and cooling in different parts of the year.

In most cases they require heat gains in winter and solar blocking in the summer, but in some situations cooling is a higher priority while in others it's the opposite - something that can make the selection of windows in these climates a bit more difficult...

A low U-factor will ensure that both air conditioning (in summer) and heated air (in winter) will be kept inside home. That is, a low U-factor is important in almost all mixed climates… So: choose windows with low U-Values, if you live in a mixed climate.

As to the issue of the SHGC, that's more complicated... A moderate SHGC (around 0.40, say) will keep part of the sun’s heat outside, while a lower SGHC (less than 0.30) will mean less free heat in the winter, though also lower cooling costs in the hot time…

To deal with these possible opposite goals, and to maximize the benefits, you may consider south facing windows (or north facing windows, in the southern hemisphere) with a moderate-high SHGC, to receive valuable solar heat in winter… And also a moderate-high SHGC for the windows in the opposite side of the house, where harnessing low levels of natural light and heat provided by the sun is the more important…

As for east- and west facing walls, since they receive more sunlight and heat in summer and hot weather conditions - an undesirable feature -, choosing low-SHGC windows is often the best option.

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USA Four climate zones for Windows

In USA, Energy Star considers four climate zones for qualified windows, doors, and skylights:

Northern: colder climates, demanding mostly heating windows
North/Central: temperate mixed climates
South/Central: temperate mixed climates
Southern: warmer climates, demanding mostly cooling windows

Source: www.energystar.gov

See also: Detailed State US table with climate zones for windows, doors and skylights

U-factor and SHGC values recommended for these American climate zones

Windows:
Northern climates: U-factor: <0,35; SHGC: any
North-Central climates: U-factor: <0,40; SHGC: <0,55
South-Central climates: U-factor: <0,40; SHGC: <0,40
Southern climates: U-factor: <0,65; SHGC: <0,40

Skylights:
Northern climate: U-factor: <0,60; SHGC: any
North-Central climate: U-factor: <0,60; SHGC: <0,40
South-Central climate: U-factor: <0,60; SHGC: <0,40
Southern climate: U-factor: <0,75; SHGC: <0,40

AUSTRALIA
Climate Zones for Windows

Image Source: www.greenhouse.gov.au

Australian Window Energy Rating Scheme (WERS) considers eight Australian climate zones within three main climate zones (cold, hot and mixed). Windows are rated from 0 to 5 stars both for cooling (summer) and heating (winter).

 

CANADA
Climate Zones

The Canadian authorities consider four different types of climates and qualified windows, doors and skylights.

See: ####

 

US climate Zones
for Windows, Doors and Skylights

TYPE OF WINDOWS, DOORS AND SKYLIGHTS
State	Climate Zone Window
Alabama	South/Central or Southern
Alaska	Northern
Arizona	Northern or South/Central
Arkansas	South/Central
California	South/Central
Colorado	Northern or North/Central
Connecticut	Northern
District of Columbia	North/Central
Delaware	North/Central
Florida	Southern
Georgia	South/Central or Southern
Hawaii	Southern
Iowa	Northern
Idaho	Northern
Illinois	Northern or North/Central
Indiana	Northern or North/Central
Kansas	Northern or North/Central
Louisiana	Southern or South/Central
Kentucky	North/Central
Maryland	Northern or North/Central
Massachusetts	Northern
Maine	Northern
Michigan	Northern
Minnesota	Northern
Mississippi	South/Central or Southern
Missouri	Northern or North/Central
Montana	Northern
Nevada	Northern or South/Central
New Jersey	Northern or North/Central
New Mexico	North/Central or Northern
North Carolina	North/Central or South/Central
North Dakota	Northern
Nebraska	Northern
New Hampshire	Northern
New York	Northern
Ohio	Northern or North Central
Oklahoma	South/Central
Oregon	Northern
Pennsylvania	Northern
Rhode Island	Northern
South Carolina	South/Central
South Dakota	Northern
Tennessee	North/Central or South/Central
Texas	South Central or Southern
Utah	Northern or South/Central
Vermont	Northern
Virginia	North/Central
Washington	Northern
West Virginia	Northern or North/Central
Wisconsin	Northern
Wyoming	Northern