Understanding Energy Efficiency Ratings: What They Mean for Your Windows and Doors

Window Efficiency Ratings… What Are They?

Understanding Energy Efficiency Ratings: What They Mean for Your Windows and Doors

Energy efficiency ratings or energy performance ratings are grades, if you will, to determine how energy-saving a window, door, or skylight is. According to the NFRC, the average American will spend $1,500-$2,500 on Energy Bills, and 45% of that number is the cost of heating and cooling.

What is the NFRC?

The National Fenestration Rating Council or the NFRC is a third-party organization that tests, certifies, and labels windows, doors, and skylights in energy performance.

Energy Efficiency 101

Energy Efficiency ratings fall into four main categories: U-Factor, Solar Heat Gain Coefficient, Visual Transmittance, and Air Leakage. The NFRC has chosen these categories based on how a window, door, or skylight might lose or gain heat including direct heat transfer, thermal radiation, solar radiation, and, of course, air leakage.


U-factor is a measurement of the rate at which your window, door, or skylight transfers non-solar heat flow. That means that the U factor is the category that correlates with direct heat transfer and thermal radiation. U-factor can only apply to the glass and glazing, but the NFRC takes the whole window unit into account. The lower this measurement is the better your window, door, or skylight is at keeping heat from escaping.

Solar Heat Gain Coefficient

Solar Heat Gain Coefficient (SHGC) correlates to, you guessed it, solar radiation. The SHGC measures how well your window, door, or skylight can resist unwanted heat gain. This number is especially important for us here in the South, as we want those Georgia summer temperatures to remain outside of our homes. The lower the number for this category means less unwanted heat gain, therefore you’ll spend less on your air conditioning.

Visual Transmittance

Visual Transmittance(VT) measures how well your window, door, or skylight effectively lights up your home with natural light. This measurement is expressed as a number between 0 and 1. The higher the number, the more natural light is let into your home. The lower the number, the less natural light is let in.

Bonus Rating: Light-to-Solar Gain

Light-to-solar gain is a number that shows the correlation between visual transmittance(VT) and solar heat gain coefficient(SHGC). It offers a measure of how the different glasses or glazes of a window, door, or skylight bring light in while also keeping heat gain low. This energy performance rating isn’t always provided, but knowledge is power is time is money. The higher this number is the more light comes through your window without adding large amounts of heat.

Air Leakage

Air leakage is the amount of air movement(drafts) that will enter a room through your window, door, or skylight. This is where it becomes really handy to have people you can trust to install your replacement windows and doors because if they aren’t installed properly, air leakage will kill your bank account via high energy bills. You want this air leakage number to be low because that means fewer drafts. Fewer drafts mean your window sits tighter in your fittings like a bug snug in a rug.

Bonus Rating: Condensation

Condensation, as we know, is when your window looks like it has its own little rainstorm happening between the panes of glass. The NFRC does have a rating for this that is an optional rating for manufacturers to include and it measures how resistant a window, door, or skylight is to condensation. The higher the number, the better the resistance.

NFRC Rating Vs. Energy Star Rating

The NFRC’s mission is to provide you with measurable data to compare different ratings across multiple products. Energy Star is a company that uses the NFRC ratings to set standards that make all of its products energy-efficient. They even break it down by climate, so no matter where you live you’re getting the best product for your location.

Great Lakes Windows and Doors

Our manufacturer is Great Lakes Window. They are an Energy Star partner and build all of their windows and doors to the Energy Star standards. Each of the products we order is custom-made, so they fill your fittings perfectly. Then, each product when they are delivered will already be labeled with the NFRC sticker that shows all of the ratings of that product. To schedule your free estimate today you can contact us here, or call us at (470) 275-5159.

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