Energy Efficient Windows, Doors and Skylights & Climate Zones  
 

New technologies allow a huge diversity of windows, doors and skylights, with different energy performances.

These performances are measured mainly by the U-factor (the rate of non-solar heat loss or gain) and the SHGC (a measure of the solar radiation admitted through a window, door  or skylight).

But the performances of a window, door or skylight shouldn't be considered in abstract. A low SHGC is a good indicator in warm or mild climates, but it isn’t relevant in a very cold climate, where the solar radiation admitted in a home is rarely negative.

In other words: energy efficient windows for UK, Massachusetts, Michigan or Minnesota aren't the same of those for Mexico, most of Australia, or Florida. Efficient windows, doors and skylights should present different U-factor and SHGC... 

Conclusion:
When purchasing a window, a skylight or a door you should demand products that are qualified for your specific climate zone. The Energy Star ratings (or the European BFRC and other ratings) are valid and applied to specific climate zones...


Climate & glasses, frames and sashes

In cold and moderate climates, the most energy efficient windows, skylights and glazed doors use low-E coating glasses, to reduce heat losses through the window.

In hot climates, the most energy efficient windows, skylights and doors use solar control glass, also called Low E2. This type of glass is the best to limit solar heat gains (it blocks the infrared and some ultraviolet rays, more than tinted window coating), besides being a good insulator and transmitter of visible light...

The frames and the sashes of windows, glazed doors and skylights should be made of vinyl, fiberglass or wood. Aluminum fenestration should only be used with insulating thermal breaks.

See for more details:
Glasses and windows, doors and skylights
Frames and sashes 

Climate zones for Windows, Doors & Skylights

Broadly we can consider three big climate types when equating the efficiency of windows, glazed doors and skylights:

- the colder climates (alpine or cool temperate) where energy is mostly used to heat the home. In this climate zones windows, doors and skylights should be selected to keep heat inside them.

- the warmer climates (or tropical, subtropical and hot arid) where energy is mostly used to cool the house. In these climate zones windows, doors and skilights should be selected to keep heat outside.

- the temperate mixed climates where windows, skylights and doors should be selected and designed  for heating in winter and cooling in summer.


USA climate zones:

In the United States of America there are four Climate Zones for Energy Star 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


The U-factor values and the SHGC in the American Climate Zones

Energy Star Windows and doors:

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

Energy Star 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
Northern climate: U-factor: <0,75; SHGC: <0,40


AUSTRALIA Climate Zones



In Australia the predominant climate is equivalent to the American Southern, with the exception of Tasmania and the southeast corner or mainland (cold climates) and the temperate southern coastline and much of NSW.

Australian Window Energy Rating Scheme (WERS) rate windows for the three big Australian climates: rated windows get from 0 to 5 stars for both cooling (summer) and heating (winter).

Image Source: www.greenhouse.gov.au


CANADA Climate Zones

Canada has been divided into four climate zones when choosing windows, doors and skylights energy performance. The scheme is very analogous to the USA system.


















Image Source: Office of Energy Efficiency Canada







US TABLE WITH 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
Mississipi	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

For more information:
  Windows, doors and skylights basics
  Windows, skylights, doors & rating
  Frames and sashes
  Advanced Doors
  Skylights
  Weatherstripping
  Caulking
  Rebates and Tax Credits


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