The efficiency of a fireplace is its ability to transfer heat, efficient use of fuel energy, and a high efficiency factor (the same one that is studied in physics classes at school). Conventional wood fireplaces have an efficiency of 20-30%.
This is not much, good indicators are from 35% to 40%. Some fireboxes can produce values twice as high – up to 80%. But a fireplace is not limited to just a firebox; it is a complex structure, a whole complex of different elements. The entire structure will definitely suffer from heat loss. It is important to know what objective and subjective factors will affect the overall productivity of the heating device.
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What Determines The Efficiency Of A fireplace?
So, here’s what affects the heat generation in a fireplace and makes it productive or unproductive in the difficult task of heating your home:
1. The firebox is a niche made of refractory bricks and is the main element in the heating system. Its depth affects efficiency – a firebox that is too deep reduces heat transfer, but its shallow depth can lead to smoke in the heated room. If the firebox is equipped with a double combustion system, its energy efficiency increases by approximately 15-20%. You can also increase heat transfer by providing the casing with convection holes: they will increase air circulation inside the chamber.
2. Lining and material for it. How is the inside of the firebox finished? According to professionals, the best option is heat-intensive fireclay stone: it is strong and durable and creates optimal conditions for burning fuel in the chamber, as it maintains a constant high temperature in it. It will also create an additional fire protection circuit and protect the furnace structure from exposure to extreme heat. Potted stone, or soapstone, has similar qualities.
3. Arrangement of a beveled plane in the rear part of the firebox – a plane located at an angle will act as a reflector of thermal radiation into the room.
4. A well-designed and constructed chimney that provides a strong draft. The intensity of heat transfer directly depends on the rate of removal of combustion products from the combustion chamber. A clogged chimney with poor air circulation from bottom to top is a real devourer of thermal energy and is fraught with the effect of an overturned draft – the release of toxic carbon monoxide into the room.
5. The airtight door allows the well-heated wall to retain heat all night. An open firebox quickly gives off heat without having time to warm up the adjacent surfaces, and the heated air easily cools down or leaves the room due to drafts. In the case of an open firebox without a damper, it is recommended to use a fireplace screen.
6. Correctly selected fuel. Over-dried firewood will burn quickly, like brushwood, and excessively wet firewood smokes more than it heats. There is a lot of smoke and sparks from resinous softwood firewood, which is why most fireplaces are designed for heating with hardwood. Birch burns cleanly, but its combustion produces a lot of soot. Firewood from alder and aspen promotes the combustion of soot, so a mixture of different types of firewood – from birch, aspen and alder – will be optimal.
7. Decorative cladding material. It should not work as a battery and heat emitter, but a fireplace portal made of soapstone or brick will increase the thermal output of heating equipment. Which devices have the maximum efficiency? These are so-called fireplace stoves . They are often operated without external decoration, and their body is made of a material that retains heat excellently and cools extremely slowly – boiler cast iron. The chimney pipe of such stoves is an additional source of thermal energy. It heats up greatly due to the hot gasses rushing upward.
About Power Indicators
The power of a fireplace or other heating equipment is determined by two types of indicators:
- The maximum is the amount of heat generated during the first half hour of operation.
- nominal is the amount of thermal energy released by a working device in 3 hours.
When purchasing a firebox for a fireplace-stove in finished form, be sure to check with the seller exactly what values are indicated in the data sheet. Sometimes manufacturers use a trick, writing more impressive maximum power figures into the technical data sheet. But the nominal value is more important if you are purchasing a heating element for your home, not a decorative element. The rated power will show the energy efficiency of the device during long-term operation.