Doors are responsible for 11 percent of air leaks in most homes, according to the California Energy Commission. Even well-sealed doors waste energy and are typically not as tightly insulated as walls. Glass in doors is particularly inefficient, but even solid doors with no glass can be significantly improved.
Energy Star-certified doors can boost efficiency and potentially save on energy bills. To be sure, homeowners in mild climates may not be able to recoup the cost of new doors through energy savings. Instead, weather stripping existing doors can solve most leaks, and is more cost-effective. However, new Energy Star doors can be a cost-effective option for new construction, existing homes in severe heating or cooling climates, glass patio doors and other situations where doors must be replaced.
Beyond looking for the Energy Star logo, look for specific ratings and features of energy-efficient doors. There are three main categories of Energy Star doors, and each category has different efficiency requirements.
Solid doors without glass are known in Energy Star lingo as "opaque" doors. The most energy-efficient options have steel or fiberglass frames and insulating polyurethane cores. To earn an Energy Star label, windowless doors must have a U-Factor less than or equal to 0.21.
The U-factor is a rating of heat transfer per hour per square foot. It is the inverse of R-factor insulation ratings. To translate the U-factor to an R-rating, divide 1 by the U-factor. This means windowless Energy Star doors are at least R-5, which is about five times the insulation value of a traditional solid wood door.
Doors that are less than one-third glass are confusingly called 1/2-lite doors. Glass allows more heat transfer than the polyurethane core, so only the most expensive triple-pane glass in a door could be expected to meet the U-factor standard of 0.21. Therefore, Energy Star doors with glass sections must reach a lower U-factor bar of 0.27 (the rough equivalent of R-4). They must also have a solar heat gain coefficient (SHGC) rating of 0.30 or less. The SHGC measures the amount of solar heat blocked by the door, and a lower number means less heat transfer, thus lower cooling bills. Keep in mind that in cold climates, higher SHGC numbers may be advantageous for passive solar heating in the winter. Unlike Energy Star's windows and skylights, Energy Star door rating values do not vary by region.
Doors with more than one-third glass, such as glass patio doors, have still looser standards. The U-factor must be less than or equal to 0.32 (or about R-3). The SHGC must still be 0.30 or less.
Look for double- and triple-layer glass, low-e coatings and argon fills or other low-conductivity gases, all of which increase energy efficiency of the doors.
Even if they have Energy Star labels, all-glass patio doors are still relatively inefficient, particularly sliding doors. They cannot seal as tightly as swinging doors. Look for swinging doors with magnetic strips that create a tight seal and prevent the need for further weather stripping in most cases.
Of course, these complex, efficient doors are more expensive. However, you can get back some of the extra expense with tax credits or rebates. Energy Star-certified doors installed in 2011 on a taxpayer's primary residence are eligible for a federal tax credit. The credit covers up to 10 percent of the purchase price, and applies toward a $500 total tax credit for all energy-efficiency upgrades.
State and local governments and utility companies may also offer rebates or tax credits for Energy Star-certified doors.
Finally, the Energy Star premium is only worth paying if the door is installed properly. Many manufacturers' warranties require buyers to use their certified installers. Check references for your potential installers, and make sure they have experience installing your specific type of Energy Star door.
To maximize savings, install expanding spray-foam insulation around the doorframe, and add airtight weather stripping if necessary.
Steve Graham is a Hometalk.com - http://www.hometalk.com - writer. Read more articles like this one - http://www.networx.com/article/energy-star-certified-exterior-doors- or get help with your home projects on Hometalk.