Energy Ratings are a measure of thermal performance that provide a good balance between the energy that could be lost through air leakage round the frame of sliding folding doors and that which is gained from the sun that shines through the glass.
Energy Ratings take into account potential heat loss, solar gain, and any air leakage that might apply to a set of doors. Once all these elements are established, the system allots a performance score for the door. This score is on a scale from A+ to G, and it is illustrated using a similar graphic to that used to measure the performance of white goods like washing machines and freezers.
All this information is very useful, but when you’re choosing a set of sliding folding doors you might also want to consider the orientation of your building before making your final decision.
An A-rated glass door will be designed to maximise the energy gained from the sun, but if you are putting big sliding folding doors in a bright south-facing room, you may find that this makes the room uncomfortably warm in the summer.
It may, therefore, be better to specify sliding folding doors with a low U-value, which will mean they’re good at conserving heat in the winter, and not worry so much about having a good energy rating.
Of course, on the north side of the house, where the sun might not be so strong, you may be glad to have a specification that maximises solar gain.