What is an open fireplace?
An open fireplace is a built or prefabricated hearth in which an open fire burns, with a direct connection to the flue. There is no door in front of it, so combustion air is drawn from the room without restriction.
That is exactly what makes an open fireplace atmospheric and inefficient at the same time. To carry the smoke away reliably it needs a strong draught, and that draught removes not only smoke but also large quantities of heated room air. The efficiency of an open fireplace is therefore in the order of 10 to 15 per cent: by far the greatest part of the heat disappears up the chimney. In a well-insulated, airtight house an open fireplace can even cost heat on balance, because the air drawn out is replaced by cold outside air that the heating then has to warm up again.
Open fireplace versus closed stove
A closed wood stove or an inset with a glass door achieves several times that efficiency, because the air supply can be controlled and the heat stays in the appliance. If you want heat, choose a closed appliance; if you want atmosphere, choose an open fire. An existing open fireplace can often be converted with an insert cassette fitted into the existing hearth.
Points to note
- Combustion air supply. An open fire needs a lot of air. Combined with an extractor hood or mechanical ventilation, negative pressure can occur and smoke will spill into the room. A dedicated air supply from outside solves this.
- Sweep annually. With wood burning, have the flue swept and the appliance checked at least once a year. Soot and creosote deposits are the cause of chimney fires.
- Burn dry wood only. Untreated timber, seasoned for at least two years, with a moisture content below about 20 per cent. Wet wood, painted wood, chipboard and waste timber produce a great deal of smoke, soot and harmful substances.
- Build the fire small and burn briskly rather than letting it smoulder; smouldering produces the most emissions and the heaviest deposits.
- Consider the neighbours. Smoke causes nuisance; avoid burning in still or foggy weather.
- A fire-safe surround — a non-combustible hearth plate in front and sufficient distance to combustible materials.
Related terms
- Flue
- Fire resistance
- Balanced ventilation
- Airtight construction
- Stove insert
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