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Understanding Window Energy Ratings

A window’s energy rating should be the first thing you look out for when shopping for new windows. You can thus use the rating indicated on each window to compare different products and preferably choose the best rated of them all. Although you might know this already, the window you choose to buy will have a direct impact on your home’s energy efficiency and security.

Investing in the most energy-efficient windows you can afford and ensure they are installed correctly, can significantly improve your home’s thermal performance and energy efficiency. Windows with the highest energy ratings have superior thermal performance that helps keep your home warm during winter and cool in summer, improving your HVAC’s performance significantly. This translates to even more energy savings in the long run. However, poorly rated windows will force your HVAC systems to work harder to keep your home comfortable, hence higher energy bills.

Energy Rating

Always check the window’s energy rating label whenever shopping for new windows. These labels will be colour-coded for easier translation, with the best performing going more to the greener zone and worst on the red zone. In other words, the window energy ratings have the same rainbow colour design as you’d find on washing machines and refrigerators.

Window manufacturers typically use a number of energy rating schemes, with the British Fenestration Rating Council (above left), CERTASS (above right), and British Standards Institute (above centre) being the most commonly used. These, however, work the same way, hence no reason for concern.

Manufacturers such as KJM Group assign a letter rating based on the window’s energy performance. All factors (frame design, material, type of glass used, an inert gas used) must be considered when measuring the windows performance. The best-performing windows have an A+ rating, with subsequent letters used progressively on lower-performing ones.

Manufacturers use a formula that takes all the aspects of the window into account to calculate the window’s letter rating. This includes solar gain, air leakage, and thermal efficiency.

Energy-Efficient Windows and Consequent Energy Savings

The window energy ratings only indicate how efficient the window itself is. Additional factors, including where the window will be located, the building’s orientation, your HVAC’s efficiency, and overall insulation, will also need to be considered before doing the installations.

Frequently Asked Questions on Window Energy Ratings

Which is the best Window Energy Rating to go for?

Manufacturers use complex computer simulations (awfully accurate) to determine each window’s energy ratings. That said, the best-rated windows (A+) will perform much better in your home than low-rated ones. Investing in these should see you record significant energy savings in the long run.

Several factors also ought to be considered when shopping for the best energy-efficient windows for your home. Material preferences, design requirements, planning restrictions, your budget will, of course, determine what windows you can go for.

What is WER (Window Energy Rating)?

This is the method used to determine a window’s overall energy performance. A strict criterion followed by computer simulations determines the most accurate rating for every type of window. Some of the factors used to determine a Window Energy Rating include:

  • Air leakage
  • Type of glass used
  • Solar gain
  • Frame material used (timber, aluminium, PVC, etc.)

At KJM, we offer a variety of high-performing and rated windows for you to choose from. We, however, only offer windows with at least a C-rating to A-rated windows. The price difference between the two is almost insignificant, a reason we often recommend A-rated windows for all our customers.

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