Passive Solar Heating

The six basic principles of good passive solar design

Site planning

Orientation of windows is the most important component in passive solar design. Because southerly exposures receive the most sun light in winter, south-facing glazing should be maximized to allow the free energy from the sun to enter and heat your home.

For maximum gains, south-facing glazing can be oriented up to 15 degrees off of due south. Glazing up to 30 degrees off of due south can still provide substantial solar gains.

Windows intended for solar gains should be unshaded by trees, soffit overhangs and adjoining building structures during the winter months.

Windows

For most locations in Manitoba, the optimum area of south facing windows should be between 6% to 10% of the heated floor area. This assumes that adequate air circulation exists to distribute the solar heat gains and that thermal storage is limited to conventional building materials.

As windows are the most important component of passive solar design, they should include high performance glazing. Triple glazed windows incorporating a low-E coating, argon gas, and insulated spacer bars are highly recommended. With the wide range of low emmissivity window coatings available on the market, it is critical that the correct coating be selected. In general, it must be a solar gain, not a solar blocking coating. Within the range of solar gain low-E window coatings, each allows varying degrees of solar energy to pass through into the home. A window’s Solar Heat Gain Coefficient (SHGC) refers to the amount of solar energy it transmits. The bigger the SHGC number the better.

Correctly selected high performance, low emissivity coated windows not only maximize solar gains but in addition, keep the majority of that heat in the house, increase condensation resistance, and improve internal comfort.

To optimize south facing glazing, the design of a few bigger windows is better than numerous smaller ones with the same area.

Skylights should be avoided as a means to collect solar energy as they are difficult to shade in summer months and end up serving as areas of high summer heat gain.

Because of their low SHGC and R-value, glass blocks tend to be a poor passive solar heat gain performer.