· Michael Blair
An open masonry fireplace draws a large volume of heated room air up the chimney to feed the fire. The radiant heat you feel in front of it is often less than the heat leaving through the flue.
Why open fireplaces lose heat
Combustion requires air, and an open fire takes it from the room — air you have paid to heat. That air is replaced by cold air drawn in through every gap in the house.
The net effect on a cold night is frequently negative, however pleasant the fire is.
Inserts and stoves
A closed appliance controls its air supply, burns at a higher temperature and radiates heat into the room rather than sending it up the flue. Efficiency is transformed.
An insert fits into an existing fireplace opening; a freestanding stove sits in the room and radiates from all sides, which is more efficient again.
- Open fireplace: pleasant, usually a net heat loss
- Insert: fits the existing opening, much higher efficiency
- Freestanding stove: most efficient, needs floor space and clearances
- Gas insert: convenience without the fuel handling
- All need a correctly sized liner
What installation involves
A correctly sized liner is essentially always required, since the original flue is far too large for a modern appliance. Clearances to combustibles and a suitable hearth are also specified.
It is permitted work, and the inspection is checking exactly the things that cause house fires.
If you keep the open fire
A tight-fitting damper, glass doors and an outside air supply all reduce the losses. Closing the damper fully when not in use is the single largest one, and it is frequently left open.
A chimney balloon or a fitted plug for an unused fireplace stops a permanent hole in the building envelope.