I am sure that the Energy Star program is not going to help me.
The USA Energy Star program helps people find energy efficient windows. It guides us to prefer windows with low U-Factor and low solar heat gain coefficient. This is good in two circumstances:
- In a climate with more cooling days than heating days, such as the southern climate zone.
- In a perfectly insulated house, in winter, that retains generated heat so well that heat from sunlight isn't welcome.
But in an old house with mediocre insulation, sunlight is welcome in winter. Windows with a higher heat gain coefficient allow the sunlight to warm the interior of the house. This can save energy, in a climate with more heating days than cooling days.
To mitigate the higher heat gain coefficient on a hot summer day, the sunlight can be blocked with a blind. This can be done very efficiently using a blind on the exterior of the window or embedded within the window (i.e. between two panes of a multi-pane window).
The USA Energy Star program steers people away from using windows in this way. As a result, homeowners in the northern climate zone, in older houses, are installing windows that help them in summer months. But many of these people might really benefit financially from windows that help them in the winter instead.
If you compare the USA Energy Star program to the Canada Energy Star program, you'll see a difference in priorities. As a result, certain windows (with higher heat gain coefficient) that are Energy Star certified in Quebec are not certified in Maine.
There are parts of the USA where heating costs are relatively higher, because passive cooling is relatively easy and effective. In these parts, costs can be reduced more effectively using windows with high heat gain coefficient.
Update: Please do not turn this into a political discussion.
I think the answer has to do with the subtlety of cost savings versus comfort, as benefits of windows' technical properties. It appears that the USA Energy Star program places full weight on cost savings, while in Canada the cold is so extreme that a balance between cost savings and comfort must be struck. I was hoping to find a window engineer on this forum who could explain authoritatively.
As an example of a window rating system that goes way beyond Energy Star's yes/no binary value, check the Energy Calculator provided by Canadian glass manufacturer Cardinal. It gives results of different glass products in terms of both savings and comfort. Comfort is further broken down into seasons. This level of information should be available to end consumers of framed windows, and should be incorporated into location-based government certifications.
Update 2: Efficient Windows Collaborative
I found a website, sponsored by major window manufacturers and suppliers, and originally founded by the Department of Energy, which helps consumers choose the right windows based on building location and design. It directs users to specific window types that are offered by various manufacturers.
This is much more useful than the Energy Star yes/no rating system. In addition to cost savings and comfort as attributes of window performance, it discusses condensation on window surface as well.