Low-emittance – or Low-E – windows are an increasingly common way to control temperature within the building envelope. Traditionally, windows were accepted as being “energy losers” – they lacked the insulation found in the rest of the building frame, so they were prime locations for heat to escape in winter or for cool air to escape in summer (either being conducted through the glass or slipping through cracks in the window frame).

But in the last 20 years low-E window coating has changed that. The coating is a thin film that can be applied to a normal window – at first the result was a green- or blue-tinted window, but now low-e windows can look just like traditional ones. Originally the coating was applied to the interior side of windows in cold-climate homes, because its properties prevented the conduction of heat. At the time, the technology could not be put to use in warm climates, to keep heat on the outside of the window, because the coating would have blocked transmission not only of the sun’s thermal radiation but also of its light.

Modern low-E windows, however, can be used to save energy in all climates, because the coating can now distinguish between light rays and thermal rays, permitting the sunlight to enter the building envelope while bouncing the heat back. About half of all new homes are built with low-emittance windows. When you’re in the market for a new home, be sure to look for a house with low-E windows – whether you live in a cool or warm climate, they will reduce heat transfer and energy bills, making a traditional energy loser into an environmental triumph.

Check out this site for more information.

One of the most immediately appealing ways to conserve energy in your home is through passive solar heating. It is a method completely distinct from the use of solar cells; passive solar designs don’t convert energy – they just make better use of the stuff that’s already there! To take full advantage of the ways you can use the sun to heat your home, it’s best if you can design it from the ground up, so passive solar heating is most useful for buildings in the planning stages. But through moderate re-modeling you can help your existing home make much better use of natural light and heat.

When you have a great deal of sunlight entering your home through windows, you have provided yourself with a sufficient amount of heat when the sun is shining. But on cloudy days and at night, you will still need to rely completely on your traditional heating system – unless your home has a built-in way to store the sun’s heat. There are several home designs that can achieve this.

Passive heat storage systems absorb and store the excess thermal energy that enters a well-designed passive solar home during the day. In most cases the heat is stored in the masonry of a house, or its walls, floors and ceilings, which can be made of a number of heat-conducting materials.

For more thorough information on passive heat storage systems, please visit:

Arizona Solar Center – a very thorough list and description of several heat storage systems

In buildings that use the sun as a heating source, the most important element of design is a southerly exposure, and windows are the most common form.

Window Position

Your windows must face south so the sun has maximum exposure into the house, although you will lose only about 10% of the potential solar radiation by placing solar windows up to 25 degrees to the east or west of true south.

Window Size

The size of your windows is very important: if they are too small your home will miss out on the full benefit of the sun, but windows can also be too big, leading to overheating, even in winter. The recommended size ranges for windows in passive solar homes vary according to climate and latitude. For Pittsburgh, whose average temperature in January is 27 degrees and whose latitude is 40.440 N, the recommended ratio is .25 square feet of window for every 1 square foot of space floor area. Therefore a 200-square-foot space will need 50 square feet of south-facing windows. This ratio will keep your space at an average temperature of 65-70 degrees during the day.

Window Alternatives

If your wall space is otherwise occupied, or if you’d like to mix things up a bit, try using skylights, Sola Tubes or clerestories throughout your home as well. The passive-solar-heating principles are similar. In fact, clerestories offer some benefits over windows in that, if they’re designed correctly, they can accept “low angle” winter sun while preventing “high angle” summer sun from entering and overheating your home.