Your Skylight Looks Cool, but is it Wasting Energy?

Because there’s nothing like natural light for indoor illumination, a skylight is an important addition to many homes. Available in a variety of configurations, skylights perform like windows, admitting light and heat energy from sunlight during the day and radiating heat energy from the house at night.

Homeowners can choose from either plastic or glass glazing with these characteristics:

Plastic is less expensive and less likely to be broken than glass. However, the clarity and strength of crystal clear plastic may degrade after years of exposure to UV rays.

Glass is the more costly option but maintains clarity very well. While standard glass may be more likely to shatter than plastic, tempered or laminated glass is rated to resist common impacts. Heat gain and heat loss from skylights may waste energy as your A/C or furnace runs longer and works harder to compensate. Consider these energy-conserving factors when selecting a skylight:

• Heat-absorbing tints applied to glass reduce the infiltration of solar heat but also reduce visible light transmission.
• Insulated skylights feature two or more sandwiched panes of glass with the gap between the panes filled with an inert gas to decrease heat gain and loss.
• Low-emissivity (low-E) coatings apply a microscopic layer of metallic oxide to lower the amount of heat gain through the window by 40 to 60%, while still maintaining light transmission.

Two specifications are useful to evaluate the energy efficiency of skylights:

• U-factor expresses the rate of non-solar heat flow. The lower the U-factor rating, the less heat is transmitted through the skylight glazing.
• Solar heat gain coefficent (SHGC) is a fraction that expresses solar radiation passing through a skylight. A lower SHGC around 0.27 means it reduces solar heat gain in summer, while a high SHGC of 0.60 or more tends to hold more heat inside the house on cold days.

At Sobieski Services, Inc., our goal is to help our customers in Delaware, Pennsylvania, Maryland and New Jersey learn more about energy and home comfort issues — especially HVAC and plumbing issues — so that they can save money and live in healthier, more comfortable homes.

Photo Credit: wingerjohanne via Compfight cc