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Firmfix quality BSi kitemarks for manufacture and installation of windows, doors & conservatories

Firmfix Energy Ratings Explained

An energy rating certificate will always display the holders’ company name and the name of the window at the head of the certificate. Our window names are Efficiency for our C rated; Efficiency Extra for our B rated and for our A rated Efficiency Plus.

The energy index number can be a positive or a negative number. This indicates how much energy the window will save or lose. A positive value means the window will enable more energy to pass through the glass into the room than is going to be lost.

Thermal Transmittance (U value) measures how well a product prevents heat escaping. The lower the number the better the U value is.

Solar Factor measures how well a product blocks heat caused by sunlight.

Effective Air Leakage relates to the volume or air leakage from a window.

Energy ratings are not calculated just on the glass, the window frame is also part of the calculation.

In simple terms, A is the best at conserving energy and the higher the index number is the better. So our +8 A rated windows are amongst the best energy saving windows on the market.

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