Energy Efficient Windows

Windows provide a lot value and beauty to our homes. They provide us with light, warmth, and ventilation, but they can also affect a home’s energy efficiency. Energy-efficient windows can reduce energy costs in your home. If you’re on a fixed budget, energy efficiency improvements to existing windows can also make a big difference.

Improving the Energy Efficiency of Existing Windows

In Cold Weather

Storm windows, caulking, weatherstripping, and window treatments or coverings can dramatically impact the efficiency of your existing windows.

Window technologiesStorm windows can cut down on air leakage and improve comfort. Installing exterior or interior storm windows can reduce heat loss through the windows by approximately 10%-20%. Caulking and weatherstripping can reduce air leakage around windows. Caulk is used for stationary cracks, gaps, or joints less than one-quarter-inch wide. Weatherstripping is for building components that move, such as doors and operable windows. Window treatments or coverings can reduce heat loss in the winter and heat gain in the summer. Most window treatments, however, aren’t effective at reducing air leakage or infiltration.

If you’re on a tight budget, you can use a heavy-duty, clear plastic sheet on a frame or tape clear plastic film to the inside of your window frames to reduce drafts. You can install tight-fitting, insulating window shades on windows that feel drafty after weatherizing. Remember to close your curtains and shades at night to protect against cold drafts; open them during the day to let in warming sunlight.

In Warm Weather

Installing white window shades, drapes, or blinds can reflect heat away from the house. Closing curtains or installing awnings on south- and west-facing windows can make also provide relief from the heat. Tinted and other reflective films on south-facing windows can reduce solar heat and glare.

Choosing New Energy Efficient Windows

New, energy-efficient windows eventually pay for themselves by lower heating and cooling costs, and sometimes even lighting costs. The Efficient Windows Collaborative has put together this handy Texas Fact Sheet that explains what types of windows are good for Central Texas.


Before choosing new windows for your home, find out what types of windows will work best and where to improve your home’s energy efficiency. It’s a good idea to understand the energy performance ratings of windows so you’ll know what you will need for your windows based on your local climate and the home’s design. ENERGY STAR® has established minimum energy performance rating criteria by climate. However, these criteria don’t account for a home’s design and window orientation.

Passive solar home design uses the floor plan and orientation to maximize the sun’s available energy in cold climates or minimize it in hot climates for heating, cooling, and lighting for a house. There’s a wide variety of passive solar design strategies according to building location and the regional climate, but the basic window rule of thumb remains the same—select, orient, and size glass to maximize solar heat gain in winter and minimize it in summer.

In hot climates, windows facing south can collect solar heat during the winter when the sun is low in the sky.  When the sun is high overhead in the summer, awnings and other shading devices can prevent excessive heat gain.


Buying New Windows

Low-E coatings are microscopically thin, almost invisible metal or metallic oxide layers deposited directly on the surface of glass that control heat transfer through windows with insulated glazing. Tinted glass will absorb a large amount of the incoming heat and light through a window, reflective coatings reduce the transmission, and spectrally selective coatings filter out 40% to 70% of the heat normally transmitted through insulated window glass while allowing the full amount of light to shine through.

Building a New Home 

If you’re building a new home or undertaking a major remodel, you should also take advantage of the opportunity to use your window design and selection as an integral part of your whole-house design—an approach for building an energy-efficient home.

When selecting windows for energy efficiency, it’s important to first consider their energy performance ratings in relation to your climate and your home’s design. The U-factor is the rate at which a window, door, or skylight conducts non-solar heat flow. The Solar Heat Gain Coefficient (SHGC) is the fraction of solar radiation admitted through a window, door, or skylight — either transmitted directly and absorbed, and then released as heat inside a home.

Look for windows with both low U-factors and low SHGC’s to maximize energy savings in temperate climates with both cold and hot seasons. Look for whole-unit U-factors and SHGC’s, rather than center-of-glass (COG) U-factors and SHGC’s. Whole-unit numbers more accurately reflect the energy performance of the entire product.

Proper Window Maintenance

Proper Window RepairDouble-paned windows can fail over a period of time, especially when exposed to excessive heat and sunlight. That is why the windows on the east, south and west sides of your home are most prone to failing. You do not have to do a total replacement. You can just replace the sealed units of your windows and not the whole windows. There are local services to do window repair for you. Here are some photos of my failed windows and my window repair. You can see the “fog” or moisture inside the windows and then how clear and wonderful they look after replacement of the window inserts. On this photo, you can see the fog that has formed between the double panes on the left and the clarity of the replaced panes on the right.