A stove is a closed appliance. Therefore, its air intake is controlled by the user by the means of primary and secondary air flow controls which control how quickly the fuel burns.
What is an open fire ?
An open fire is just that, .. a fire sat within an opening on a grate/ insert into an open flue/ chimney. The only control you have (other than a damper plate in some kinds) over an open fire is the amount of fuel you use in it.
What are the differences in efficiency?
A typical open fire will have an efficiency of approximately 5-35% on a 24-hour cycle; with a maximum of around 60% efficiency.
The efficiency of a stove varies with design but must have a minimum efficiency of 65%. Most modern stoves average around 80% efficiency with some exceeding 95%.
The stove is undoubtedly safer when in use, as the flame is contained within a cast iron or steel box and behind a piece of toughened glass. An open fire has no safety features except for maybe an aftermarket mesh spark guard. Perhaps surprisingly, statistically, chimney fires are much more likely when wood burning stoves are installed. Individual users often over-regulate the air supply causing the fire to slumber or they burn wet wood (>20% moisture).
The initial outlay is more expensive when installing a stove mainly due to the costs of a suitably sized liner but its’ running costs are very much lower due to its’ higher efficiency. This is achieved by being able to regulate the air intake on the appliance and having a physically smaller burning area than most open fires. Also, less fuel is required to get the same heat output from a stove.
The open fire is a clear winner here.
An open fire is seen as a primal thing… you really feel like the fire is in the room with you and it certainly is the focal point of any room. The smell, crackle, and roar of a true open fire simply cannot be beaten. Whilst the stove has a controlled burn for efficiency, toast and melted marshmallows taste better on the open fire.
To put this in perspective open fires burning anything but smokeless coal have been banned from virtually every major city in the UK due to the smog they produced in the 1950’s and 60’s. There is an argument today that wood burning stoves produce particulate emissions similar to that of diesel cars but this is also true of open fires though and in much higher concentrations than in a quality closed appliance.
An open fire must have an air vent somewhere in the room of the appliance and this must have a minimum free air space of 50% of the cross-sectional area of the throated part of the flue. This is indeed a large vent and in most cases brings in lots of cold air. Whereas most stoves under 5 Kw do not require additional ventilation unless installed in a new build property post-2008.
Open fires and stoves work in different ways. Due to the uncontrolled nature of an open fire and the weak draught caused by diluted flue gases from the room. It must have a large air flow in order to evacuate the exhaust fumes from the room.This is accommodated by having a minimum 200 mm diameter sized flue.
A stove, on the other hand, requires a powerful draught to draw air forcefully into the firebox through the small air intakes. This is done by having a much smaller diameter flue, often with a smooth internal surface that often gets hot and is helped by additional insulation around the liner.
The stats clearly show that the stove takes the prize for efficiency and economics but you really can’t beat a natural flame fire for the feeling of home comfort.