Awnings effective for reducing air-conditioning costs

Dear Jim: I like an outdoor view, so I keep shades open, but the sun's heat coming in is intense. I like the way window awnings look. Can you tell me how to determine what sizes I need and what materials are best?--Sean H.
Fabric awnings with sides block sun from the windows throughout the entire day. Notice how it also shades the window air conditioner for greater efficiency. Photo courtesy Aristocrat® Awnings by Craft-Bilt
Fabric awnings with sides block sun from the windows throughout the entire day. Notice how it also shades the window air conditioner for greater efficiency. Photo courtesy Aristocrat® Awnings by Craft-Bilt

Dear Jim: I like an outdoor view, so I keep shades open, but the sun's heat coming in is intense. I like the way window awnings look. Can you tell me how to determine what sizes I need and what materials are best?-Sean H.

Dear Sean: Awnings can be extremely effective for blocking the sun's heat and reducing your air-conditioning costs. Tests have found properly-sized awnings can lower cooling requirements by up to 20 percent. Your actual savings depend upon your climate, location and air-conditioning habits.

Closing shades and curtains can help somewhat by keeping the heat near the window, but the heat is already inside your house. Because of the greenhouse effect, this heat just inside the window does not easily go back outdoors.

Window glass is transparent to the short-wavelength heat energy from the intensely hot sun. This heat energy becomes long-wavelength infrared heat energy once through the glass and inside your house. Since glass is fairly opaque to infrared heat, it gets trapped indoors.

By sizing awnings properly for your area's latitude, they can block the direct sun's heat during summer, yet allow the sun's rays through during winter. With the sun's position lower in the sky during winter, it shines indoors underneath the awning for free passive solar heating.

The size of an awning is more important than its material for energy efficiency. Both fabric and metal, often aluminum, block the sun's direct rays. Fabric may offer more style and color flexibility, but metal is very durable, especially in harsh climates with much snow and storms.

You can calculate the best size of awning using high school trigonometry and a monthly sun-angle chart for your area. When attempting this, keep in mind the sun is lower in the sky during early morning and later afternoon than at noon.

If your house has large roof overhang, that may adequately shade south-facing windows. Also consider the location of trees which may shade some windows at certain times of the year. Good-quality awnings are not cheap, so the fewer your need to install, the better for your budget.

If your math skills are not what they used to be, make up simple cardboard test awnings of various sizes. First shop for the style of awning you like and its angle so you can simulate it with your cardboard ones. The ones for the east- and west-facing windows will be larger.

For the most effective shading, adjustable awnings are a good option. The distance they project out from the window can be changed as the sun's position in the sky changes throughout the summer. Some can even be lowered flat again the window to offer some protection during storms. Awnings with sides can offer an extra hour or two of shade on south-facing windows.

The following companies offer window awnings: Awntech, (800) 200-5997, www.awntech.com; Craft-Bilt, (800) 422-8577, www.craftbilt.com; Durasol Awnings, (888) 387-2765, www.durasol.com; Eastern Awning, (800) 445-4142, www.easternawning.com; and General Awnings, (888) 768-8404, www.generalawnings.com.

Dear Jim: We use a heat pump year-round in our house. It seems like the room temperatures stay more constant if we run the blower continuously. Is doing this saving or wasting more electricity overall?-Mike J.

Dear Mike: There are couple of factors that determine whether you are saving electricity. If running the blower continuously has improved your comfort to the point you set the thermostat several degrees lower during winter and higher during summer, then you will save electricity.

Also, if you have a variable-speed ECM-type of blower motor, it uses much less electricity than a standard blower motor in the slow-speed mode. Check with your HVAC contractor.

Send inquiries to James Dulley, The Forum of Fargo-Moorhead, 6906 Royalgreen Drive, Cincinnati, OH 45244, or visit www.dulley.com