Understanding energy ratings on windows is often seen as a simple yet misunderstood topic, but it doesn't have to be perplexing. Window energy ratings, also known as Window Performance Ratings, measure the amount of heat lost or gained through windows in a building. This measurement is a crucial factor in determining how energy-efficient your windows are.

These ratings are based on a series of tests that assess the energy performance of different window designs and materials. The most common method used in many countries to calculate window energy efficiency is called the 'WERE rating system', which stands for Window Energy Efficiency Scheme. This system provides a unique number or star rating that indicates the overall energy efficiency of the window.

The WERS rating system uses a scale between 0 and 1000 to evaluate the energy performance of windows. This number takes into account various factors such as the U-value of the window (which determines how much heat is lost) and the Heat Transfer Coefficient of the window (which determines how much heat is gained). The U-value is measured in cubic feet per second (W/m2K) and is an inverse measure of the amount of heat that escapes through a window.

Windows with lower U-values are more energy-efficient and will provide better insulation, while windows with higher SHGC values allow more solar heat to pass through. Generally, a window with a U-value of below 1.8 W/m2K is considered to be highly energy-efficient.

In addition to the WERE rating system, windows are also rated based on their numerical rating, which ranges from 1 to 5 stars. The numerical rating system is designed to be more accessible and provide users with a quick and easy way to understand the energy efficiency of windows. The more stars a replace fogged window glass has, the higher its energy efficiency and the better it performs.

It's worth noting that these energy ratings can also vary based on different factors such as the window's composition, support system, gas fill, and treatment. Therefore, it's essential to compare different windows with similar features to get a clear picture of their energy efficiency.

When buying new windows, it's crucial to consider the window energy rating as a key factor in your purchasing decision. This can help you save money on your energy bills in the long run and contribute to reducing your environmental impact.