Do you choose UPVC or wood? Do you go for partial double glazing? Do you want to replace all your windows and doors and perhaps install a double glazed conservatory? Maybe even Faux Sash Windows could be appealing (find out here: What are Faux Sash Windows?).
the introduction of double glazed windows into many homes; this technology has helped to insulate one of the most vulnerable parts of our homes with regards to heat loss.