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.

An essential component of conserving energy is keeping conditioned air in your house and keeping unconditioned air out, meaning that in the winter hot air doesn’t escape and in the summer cool air doesn’t escape. Insulation plays a role in keeping your house warm too, but regular fiberglass insulation does not stop the flow of air. Typically insulation is effective at preventing heat transfer through materials (limiting your home’s ability to conduct heat), it cannot prevent air from actually sneaking in and out through holes and cracks. (The exception to this is sprayed-in Cellulose and some foam insulations that can both air seal and insulate)

The most significant air leakage occurs at cracks in drywall, most often at barriers between the conditioned area of the house and the attic, basement and crawlspace. Cracks along the sides of windows, doors and outside walls are also significant sources of leakage. Many steps toward sealing your home are best done during construction, but some improvements can be made to an existing home structure – and are relatively inexpensively. According to the EPA’s Energy Star Program, air leakage accounts for between 25 to 40 percent of heat loss, so air sealing can really pay off. A good first step toward air sealing is to perform a blower-door test to determine where your home’s leaks are.

When you are air sealing your home, keep in mind that all enclosed spaces also need ventilation. Circulation between stale air from the house, which contains carbon dioxide, household chemicals and other pollutants, and outside air is crucial. But installing a ventilation system is both more effective and more energy-efficient than allowing drafts to sweep through your home whenever it happens to be windy.

For more information, please visit:
A Fact Sheet from the Department of Energy’s Web Site for Energy Efficiency and Renewable Resources

The EPA’s Guide to Home Ventilation

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