Windows, Skylights and Doors

Installing energy-efficient windows, skylights, and doors in a home will help reduce heating and cooling costs and save energy. Consumers can buy ENERGY STAR qualified windows, skylights, and doors.

The energy performance of windows, skylights, and doors can be measured in terms of two factors: the U-factor and the solar heat gain coefficient (SHGC). U-factor is defined as the rate at which a window, door, or skylight conducts nonsolar heat flow; the lower the U-factor, the more energy-efficient the window, skylight, or door. SHGC is the fraction of solar radiation admitted through a window, skylight, or glazed door and ultimately released as heat in a home. The lower a product’s SHGC rating, the less solar heat it transmits. Products with a low SHGC rating can effectively reduce cooling loads during the summer by blocking heat gain from the sun, and products with a high SHGC rating can effectively collect solar heat during the winter. For windows, skylights, and doors, climate determines the best U-factor and SHGC rating; appropriate U-factor and SHGC values for U.S. climatic zones are provided here.

In addition to the climate, other factors affecting the choice of new, energy-efficient windows are building design, window orientation, and external shading. Consumers should also consider the type of window frame and the type of glazing or glass desired. Examples of window frame materials include fiberglass, vinyl, wood, composite wood products such as particleboard, and metal. The thermal performance of window glazing or glass can be improved by using reflective coatings, low-emissivity coatings, spectrally selective coatings, and heat absorbing tints or by filling the space between the glass panes with air or inert gases (such as argon) to increase resistance to heat flow.

The energy efficiency of existing windows can be improved by adding storm windows, caulking, and weatherstripping, which can help reduce air leakage and save energy. In addition, window treatments such as awnings, shades, blinds, and draperies can help reduce heat loss in the winter and heat gain in the summer. The U.S. Department of Energy’s (DOE’s) website provides other tips on increasing the energy efficiency of windows.

The selection of skylights depends on the home’s design as well as the local climate. Skylights must be installed properly to maximize their energy performance, giving careful consideration to their specific location on a house’s roof, their slope, and waterproofing measures. The specific location and slope of a skylight affects its daylighting potential and the solar heat gain through it. Skylight glazing is usually made from plastic or glass. Skylights can also have heat-absorbing tints, insulated glazing, and low-emissivity coatings to reduce unwanted solar heat gain in the summer and heat loss in the winter. Typically, the size of the skylight should not exceed 5 to 15 percent of the room’s floor area, depending on the number of windows.

As with windows and skylights, the selection of energy-efficient exterior doors depends on the local climate, building design, and energy performance metrics such as the U-factor and the SHGC for glass portions of the door. Insulated steel and fiberglass doors are generally more energy efficient than wood doors. Because glass is a poor insulator, modern glass doors reduce energy loss through features such as multiple layers of glass, low-emissivity coatings, low-conductivity gases placed between the glass panes, and a plastic insulator between the inner and outer parts of a metallic door frame. If an existing exterior door is old but still in good condition, consumers can consider adding a storm door. Storm door frames are usually made of aluminum, steel, fiberglass, or wood, and they may have low-emissivity glazing. DOE’s webpage on doors provides more information on the different types of doors that are available and offers tips on installing and air sealing doors to minimize energy loss.

Heating and Cooling Systems

When replacing heating and cooling equipment, consumers should consider ENERGY STAR qualified equipment that can help save energy and reduce heating and cooling costs. ENERGY STAR qualified room air conditioners and central air conditioners use about 15 percent less energy than do conventional models. ENERGY STAR qualified ductless heating and cooling systems could reduce home heating and cooling costs by 30 percent. Annual fuel utilization efficiency ratings for ENERGY STAR qualified furnaces and boilers are higher than those for conventional models. Similarly, ENERGY STAR qualified electric air-source and geothermal heat pumps have higher energy-efficiency ratings than do conventional models.

Consumers interested in using space heaters should note that ENERGY STAR qualified space heaters are not available. Portable or space heaters typically are used to heat a room or supplement inadequate heating in a room. Special care should be exercised while using space heaters to prevent burns or fire. The U.S. Department of Energy’s webpage on portable heaters provides detailed information on guidelines to be followed when buying, installing, and operating space heaters.

Programmable Thermostats

Programmable thermostats can be set to reduce heating or air conditioning operations when residents are sleeping or not at home; for maximum efficiency, these periods should last at least four hours. Programmable thermostats can store six or more daily temperature settings that can be manually overridden without affecting the rest of the daily or weekly program.

Maintenance of Heating and Cooling Systems

Proper maintenance of heating systems such as furnaces and boilers is essential for efficiency and good indoor air quality. Consumers should consider retrofitting furnaces and boilers to increase their efficiency or replacing older systems with modern high-efficiency models. Consumers must ensure that chimneys carrying heating systems’ combustion byproducts out of homes are functioning properly and that the heating system is properly ventilated. Detailed information on cleaning air ducts in homes is provided on the U.S. Environmental Protection Agency’s website.

Regular maintenance of an air conditioner's filters and coil can also help save energy and ensure efficient functioning of the unit. During the cooling season, consumers should clean or replace their air conditioner’s filters every one to two months. Clogged and dirty filters obstruct normal airflow, which causes air to bypass the filter and carry dirt into the air conditioner’s evaporator coil; this impairs the coil’s capacity to absorb heat and reduces the air conditioning system’s efficiency. The air conditioner’s evaporator coil should be examined every year and cleaned if necessary.

Additional Measures

Other energy-saving measures include ENERGY STAR Quality Installation of the heating, ventilation, and air conditioning equipment to improve its efficiency; sealing and insulating ducts to minimize energy losses; using ceiling and window fans for cooling; installing cool roofs to reduce heat gain; adding the appropriate amount of insulation to roofs; installing green roofs to insulate buildings and reduce stormwater runoff; and incorporating passive solar design techniques to reduce heating and cooling costs.

To learn more about energy-efficient heating and cooling systems, visit the following links:

• A Guide to Energy-Efficient Heating and Cooling
• Central Air Conditioning
• Room Air Conditioners
• Furnaces and Boilers

Water Heating

Consumers should consider replacing their water heater with an energy-efficient water heater, especially if it is more than seven years old. Several types of ENERGY STAR qualified water heaters are available, including high-efficiency gas storage, high-efficiency electric storage, gas tankless, and solar.

Consumers should also consider installing a drain water heat recovery system to recover heat energy from already used hot water in showers, bathtubs, sinks, dishwashers, and clothes washers, and use it to preheat cold water entering the home’s water heater or other water fixtures.

Proper settings and regular maintenance of water heaters also help save energy and reduce heating costs. A water heater’s thermostat should be set at a maximum of 120° Fahrenheit to save energy while still having water that is comfortably warm for most uses. The water heater’s tank should be cleaned every three months to remove sediment buildup, which can impede heat transfer and reduce the heater’s efficiency. To reduce energy loss, consumers can insulate the water heater’s storage tank and the first six feet of plumbing attached to the storage tank. (The water heater’s top, bottom, thermostat, and burner compartment should not be covered.)

To learn more about water heaters and energy-efficient water heating, visit the following links:

• Selecting a New Water Heater
• Sizing a New Water Heater
• Storage Water Heaters
• Tankless or Demand-Type Water Heaters
• Heat Pump Water Heaters
• Tankless Coil and Indirect Water Heaters
• Solar Water Heaters
• Estimating Costs and Efficiency of Storage, Demand, and Heat Pump Water Heaters
• Water Heating Products and Services

Water Efficient Fixtures

Repairing leaks in water pipes and fixtures and installing low-flow faucets and showerheads are effective ways to conserve water, reduce water heating costs, and save energy. In addition, consumers can also use products bearing the WaterSense label such as showerheads, bathroom faucets, toilets, and irrigation controllers, which meet water efficiency and performance standards set by the U.S. Environmental Protection Agency (EPA). New homes can earn the WaterSense label by incorporating various water efficiency features that are described on EPA’s website.

Appliances and Electronics

Consumers interested in buying new kitchen, laundry, and other home appliances and electronics are encouraged to buy ENERGY STAR qualified products. Appliance shoppers should look for the EnergyGuide label, which shows the appliance’s annual energy consumption and operating cost and makes comparing the energy use of similar models easy.

For more information on energy-efficient home appliances and electronics, visit the following links:

• ENERGY STAR: All Certified Products
• Tips: Kitchen Appliances
• Tips: Laundry
• Tips: Home Office and Electronics

Lighting

Lighting accounts for about 10 percent of an average household's energy bill. Homes can be lit through natural daylight and artificial lighting. To reduce the need for artificial lighting during daylight hours, consumers should use windows and skylights to bring sunlight into their homes.

As of January 2014, a new federal law bans the manufacture and import of traditional 40- and 60-watt incandescent bulbs. For artificial lighting, consumers should instead use energy-efficient light bulbs such as halogen incandescents, compact fluorescent lamps (CFL), and light-emitting diodes (LED). These bulbs are available in a wide range of colors and light levels. Although energy-efficient bulbs typically cost more than traditional incandescents, they use less energy and last longer, saving money over their lifespan.

For example, halogen incandescent light bulbs are about 25 percent more efficient than traditional incandescent bulbs and last up to three times longer. Similarly, ENERGY STAR qualified CFL bulbs use about 75 percent less energy and can last up to 10 times longer than traditional incandescent bulbs. Because CFLs contain a small amount of mercury, they should be disposed of properly if they break or burn out; the U.S. Environmental Protection Agency’s website outlines CFL cleanup and safe disposal steps. ENERGY STAR qualified LEDs use even less energy than CFLs and can last up to 25 times longer than traditional incandescent bulbs. The U.S. Department of Energy’s website compares the energy savings, annual cost savings, and bulb life of a traditional incandescent bulb with those of energy-efficient bulbs.

CFLs and LEDs can also be used for outdoor lighting of pathways, steps, and porches. LEDs are durable and work well in cold climates. Bare spiral CFLs used as outdoor lights should be placed in enclosed fixtures to protect them from inclement weather. CFLs and LEDs can also be used as floodlights in exposed fixtures.

Light bulbs should be placed in ENERGY STAR qualified fixtures, which distribute light more efficiently than do standard fixtures. These fixtures are available in various styles and offer features such as dimming, automatic daytime shutoff, and motion sensors, which help save electricity by lowering light levels or turning lights off when they are not needed.

For more information on energy-efficient lighting, visit the following links:

• ENERGY STAR: Light Bulbs and Light Fixtures
• Tips: Lighting
• Efficient Lighting Strategies
• When to Turn Off Your Lights
• Lighting and Daylighting Products and Services
• Certified Lighting Professionals