Understanding Window and Door Energy Performance

Especially here in the tri-state area, you often hear terms like energy efficiency, Energy Star, and R-value when researching energy saving windows and doors. In fact, if you shop for doors and windows long enough, you may hear so many terms that it can get overwhelming.

Replacing your windows and doors is one of the best home improvement projects you can do to increase the value of your home and see a return on investment. The best windows will have the perfect combination of high performance, beauty, and durability. Windows and doors usually show signs they need some TLC, so if it’s time for replacement, understanding energy performance will help you decide what to look for.

Now let’s discuss window and door energy performance using common terms, and explore important topics like glass (also known as glazing), designs, and installation.

What Does Door and Window Energy Performance Mean?

In the US, the National Fenestration Rating Council (NFRC) makes certain criteria available to consumers regarding the overall energy efficiency of a door or window. The information the NFRC has compiled is typically available on window with an Energy Star rating.

The Department of Energy, along with the Environmental Protection Agency (EPA), conducted the necessary research to determine the Energy Star rating system. 

Between the NFRC, EPA, and DOE, this set of criteria to measure energy efficiency was implemented. To qualify, doors and windows must be manufactured by Energy Star partners, independently tested by the NFRC, and pass the strict criteria required by the Energy Star rating.

How Can You Tell If a Window or Door is Energy Efficient?

Energy efficiency is usually judged by product features like low-e glass and the quality of the installation. The performance of the product is determined by the manufacturer. However, installation may be the most important because the quality of any window or door is irrelevant if not installed properly.

Door, Window, and Skylight Frames

The frame design and construction greatly affects the performance. The frames must be square, plumb, and level or the functionality will be compromised. The most energy efficient windows will be built from fiberglass, wood, or vinyl. 

Green Seal, a non-profit organization that provides labeling for consumers concerned with environmental impact from manufacturing, honored Andersen with their seal of approval. 

High Performance Glass or Glazing

Most doors and windows use a double paned, insulated glass known in the industry as low-e. This resists energy transfer and keeps your home comfortable.

Efficiency By the Numbers

The energy efficiency numbers you want to look for describe how much energy (heat or cold) the door or window lets pass through.

U-Factor

The first energy efficiency number you will encounter is the U-factor, which is an indication of how much energy the product is transferring. You will want a low number, usually between .25 and 1.25, with a lower number transmitting less energy.

Solar Heat Gain Coefficient

The solar heat gain coefficient (SHGC) number, usually between 0.0 and 1.0, indicates how much energy in the form of solar radiation the product will transfer. The lower the number, the less solar heat gain will occur.

Air Leakage, or AL

Using a formula based on how much air a door, window, or skylight will allow to pass, the AL number should be low. Most building codes will approve doors and windows with an AL number of 0.3 or less.

Visible Transmittance, or VT

VT is a simple measure of the amount of light in the visible spectrum the glass will transfer. The higher the VT number, the more light the glass will permit. You can still let the light in while limiting the harmful UV rays that can fade furniture, draperies, and carpet.

Condensation Resistance Level

Condensation or fog is usually caused by moisture that cannot evaporate, such as occurs in old windows whose seal has failed. Since the Condensation Resistance Level is measuring resistance and not transfer, you want the number to be high. Generally, look for a score higher than 50.

Where Do I Find Energy Efficient Doors and Windows in the Tri-State Area?

Ready to upgrade your home? Visit WindowRama’s virtual showroom to get inspired. We only carry brands we believe in and will work with you to get the job done right. Request a consultation with us today. 

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