Question: what is the difference between a and c rated windows?
Answer: A 'C' Rated window is still very energy efficient and could save you up to as much as £425 on your house hold bills (according to GGF). A window energy rating 'C' would be far more energy efficient than an 'E' rated window. ... Whereas a 'C' Rated window may only have a U value of 1.9W/M²K and just lots of solar gain.