Dennis Milligan of the BFCMA explores the efficiency benefits of wood-burning stoves, how they work with heat pumps, and installation essentials
Heat pumps work best when they are running at a constant temperature. A stove can complement a heat pump in cold weather by quickly boosting heat. Wood burning stoves can also provide comfortable heating for the whole house in autumn, and spring when it is not cold enough to turn on the central heating.
Heat security has also become an important consideration in severe winters. As a stove is independent of the electricity supply, it can keep the house warm when the electricity is off. Stoves are regarded as secondary heating and as such are not included in the government’s heating strategy.
Top on the list of reasons why people choose a wood burning stove is the visible warmth and comfort it creates. For many the stove is the focus of the room, with chairs and sofas arranged around it. Stove owners often talk about just how much they love the feel of the heat that comes from their stove. Another important reason, however, is financial. With the cost-of-living crisis and high energy prices being experienced, homeowners are also choosing wood burning as a cheaper alternative.
When choosing to have a wood burning stove, it is important to remember that a stove requires a chimney/flue to transport the ‘products of combustion’ to the atmosphere. At the design stage, the route of the chimney/flue within the dwelling might not appear as one of the key considerations, but it is important to plan how the chimney/flue will be incorporated in the house
at this stage. The flue gases require a clear path to the top of the flue. A straight chimney/flue is always the best solution but where this is not possible, due to the construction of the dwelling, the number of bends should be kept to a minimum and not exceed more than four. The angle of the bends should be no greater than 45° from the vertical.
(The words chimney and flue are often used interchangeably. It is the inner tube that transports the flue gases. This is the flue. The chimney is the combined inner tube and the outer casing. A clear example is a brick chimney with a stainless steel liner).
Keeping the temperature of the flue gases above the dew point is really important to allow the flue gases to freely escape to the atmosphere. Clay, concrete and pumice liners require insulation to be prepared and added onsite. Stainless steel system flues are supplied with effective insulation. Double wall pumice chimney systems have an air gap between the walls of the inner and outer blocks. This air gap combined with the natural insulating properties of pumice provides effective insulation along the length of the chimney.
Installing a stove and flue is not a DIY job. It should only be undertaken by a competent person, and the work must be approved by Building Control. England and Wales operate competent schemes which allow the registered installer to self-certify the installation. HETAS and OFTEC are two of the main companies running such schemes. Scotland and N. Ireland need to have competent person schemes and Building Control must inspect the installation.
Once installed, it is important to regularly sweep the flue. The frequency of sweeping depends on the usage of the appliance. However, as a minimum the chimney should be swept at the
start of the heating season. A build up in soot can impede the flow of the flue gases and increase the risk of a chimney fire. Remember that it is necessary to fit a carbon monoxide detector in the room where the stove is installed.
Burning dry wood not only gives more heat into the room, it also reduces soot deposits in the flue and the amount of particle emissions (PM). The Ready to Burn logo guarantees that the wood is dry enough to burn.
Concerns have been raised about particulate emissions (PM) from wood burning. The Environment Act sets out the emission limits that wood burning stoves must comply with. Many stoves already produce lower particulate levels than the Defra limits and that is where the independently verified scheme, Clear Skies, can be of assistance when purchasing a stove. The Clear Skies scheme identifies stoves that not only meet the emission limits required by Defra but also stoves that produce fewer emissions.
Wood burning is a low carbon form of heating. Logs are generally the off cuts that come from pruning trees. Woodlands need to be managed to stay healthy and part of that management is pruning. Interestingly, burning wood in a modern stove can produce less carbon than if it were left to decay on the woodland floor.
The BFCMA is the UK’s only Trade Association representing the chimney and flue industry and works closely with the Government, public bodies and other organisations to further the interest of the industry.
Dennis Milligan is president of the BFCMA