Why is the door glass small?
Big door glass = big waste of heat
Glass is a very poor insulator, which is not ideal when it comes to wood fires!
The original Pyroclassic fire did not even have a glass as the scientists wanted the fire to be as efficient as possible. Over time, consumers expressed their desire for a window into the fire which has resulted in the glass getting larger with each version.
The Pyroclassic IV has the largest door glass that can be fitted to the front of the fire as the glass retaining strips fit just inside the front opening of the fire chamber.