The 5 factors affecting the energy efficiency ratings of your windows

UK Home Improvement

The 5 Factors Affecting The Energy Efficiency Ratings of Your Windows

Inefficient windows are the major cause of loss of heat or cool from your home, which directly affects the energy consumption of your home. During winters, we use heaters to keep our house warm and during summers we use air conditioners to keep them cool, but if you have inefficient windows, these temperature-regulating systems will need to work harder and that can significantly increase your energy bill.

Instead of dealing with expensive energy bills every month, you can go for a one-time solution by investing in energy-efficient windows that help you save energy and money. The ratings of your windows energy efficiency also play a role in your savings but very few people are familiar with them. It is important to understand these ratings when buying replacement windows from Expert Window Replacement so that you can make smarter decisions for your home. 

The window rating system is important in educating the homeowners about the transmission of heat and light through a window. The energy performance rating of the window informs us about the air leaks. Having enough information about these ratings proves to be crucial in determining the expectations of your home’s utility bills along with the energy efficiency of your windows.

What Are Energy Performance Ratings?

Energy Performance rating is the scale used for measuring the energy efficiency of windows. The energy performance measurements of your windows are actually determined by the NFRC, which is the National Fenestration Rating Council, an organization authorized to certify windows, skylights, and doors based on their energy performance ratings.

The council has developed an energy performance label for educating contractors and homeowners about how a perfect window should be. And therefore windows that are highly efficient are rated so that consumers can easily compare the products based on their performance. 

Consumers can find a blue and yellow Energy Star label and the National Fenestration Rating Council label on their window’s lower right-hand corner. This can be a huge help in the buying process for the consumers.

According to the NFRC, there are typically five factors that affect that window energy efficiency rating.

Visible Transmittance

Visible Transmittance, abbreviated as VT, is a scale for how much light the window lets in, ranging for 0 to 1. The higher the number on the scale, the lighter the window allows in your homes. A lower number means your home will be relatively dimmer. It can also help you determine the energy efficiency of your home because the less light enters your home, the less solar heat it will have that will significantly reduce the heat in the house.

Condensation Resistance

Condensation resistance is a scale for measuring the amount of moisture building on the surface of windows. It is measured on a scale from 1 to 100. The lower the number on the scale, the more condensation the window allows. Condensation is actually an issue for homeowners as it can cause mould to build up.

Air Leakage

Air Leakage in your windows is important to determine its energy efficiency. Because when they are less functional, they allow the air to enter and interfere with the temperature. Typically, air leakage ranges from the value between 0.1 to 0.3, from which 0.3 is the standard building code. The less is the value, the more effective your windows will be in keeping the air out. The air leakage of the windows can change with time, and the issue can elevate because of various reasons.


The U-factor is a measure to determine how efficient are your windows in preventing heat loss. If your windows are properly insulated this will mean the windows are great in resisting the heat flow. The more the insulation of your windows, the higher will be the resistance. There are various factors measured while determining the U-factor including the frame, spacers, glazing, etc. 

Solar Heat Gain Coefficient (SHGC)

SHGC means how much solar radiation is your windows allowing inside. It can range from 0 to 1. The higher the number, the more heat is coming through the glass. It is recommended to go for the lowest SHFC rating as it can significantly minimise the use of air conditioners. 


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