Glass fronted gas fires restrict the escape of heat up the chimney .
As well as cutting heat loss up the chimney all these gas fires are convector fires and return hot air from the back of the firechamber into the room.
The overall result is a gas fire with very high efficiencies up to 87%
They need to be front fitted to allow for removal for servicing.
The heat output of the manual version is 4.4 kW