Installing a wood burning stove in your home can not only save you money on your heating bills but can also enhance the aesthetic value of your living space. Dennis Milligan of the British Flue & Chimney Manufacturers Association (BFCMA) explains more
Wood burning stoves have always been seen as a positive economic choice in times of high gas and oil prices. The Stove Industry Alliance (SIA) has reported that stove sales in the second quarter of 2022 were 40% up on last year. Households are increasingly choosing a stove as a cost-effective and efficient method of heating their living space. A stove can also be particularly effective in the spring and autumn when it is not cold enough to justify turning on the central heating.
It is clear that homeowners do not just purchase a stove to reduce the cost of heating. They also choose a stove for aesthetic reasons – the cosy, warm feeling that a wood burning stove generates. Interviews with stove owners indicate that the visual impact of wood burning in a stove enhances the feeling of warmth.
A LOW CARBON HEATING CHOICE
The BEIS Heating Strategy is based on sustainable low carbon heating solutions that can be rolled out across the country. Stoves are regarded as secondary heating, and as such are not included in their strategy. Heat pumps work best when they are kept at a constant temperature. A stove can complement a heat pump in cold weather by quickly boosting heat. Heat security has also become an important consideration in severe winter conditions. As a stove is independent of the electricity supply it can keep the house warm when the electricity is out.
Concerns have been raised about particulate emissions (PM) from wood burning. Defra published its new Environment Act last year which sets out more stringent emission limits that wood burning stoves must comply with. The new limit for particulate matter is 55% lower than the previous limit for Defra Exempt stoves. 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 offcuts 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 will produce less carbon than if it was left to decay on the woodland floor.
FLUES AND CHIMNEYS
It has been common practice to include a 200 mm flue and a standard fire opening when building a house. Wood burning stoves require a smaller flue diameter, typically 150 mm. Installing a smaller diameter flue has the benefit of substantially reducing the air loss in the SAP calculation. The general opinion is that new open fires may not be able to meet the new emission limits, and therefore it is worth checking this before deciding to have an open fire.
The stove and the associated flue/chimney should be considered as one system. The purpose of the flue/chimney is to safely conduct the products of combustion into the atmosphere. A straight chimney 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. Also, the angle of the bends should be no greater than 45° from the vertical, so the route of the chimney within the dwelling should be thought about at the design stage.
Another important consideration is consistent insulation along the complete length of the flue (the inner tube within the chimney that transports the flue gases). Clay, concrete and pumice liners require insulation to be prepared and added onsite. Stainless steel and ceramic system chimneys are supplied with effective insulation. Double wall pumice chimney systems have an air gap between the walls of the inner and outer blocks. The air gap combined with the natural insulating properties of pumice provides effective insulation along the length of the chimney. Maintaining the flue gas temperature will enable the flue gases to freely escape into the atmosphere.
CORRECT INSTALLATION
It is worth remembering that installing a stove and flue is not a DIY job. It should only be undertaken by a competent person and the work must be inspected 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.
The Environment Act also recognises the need to burn dry wood, and to regularly maintain the wood burner. Burning dry wood, and regularly sweeping the chimney or flue will reduce the build-up of soot and help keep the flue gases flowing freely. Dry wood, with a moisture content below 20% produces more heat and fewer emissions than wet wood, so the stove owner and the environment both gain from burning dry wood. Logs banded ‘ready to burn’ are guaranteed to have a moisture content of less than 20%. If you prefer to gather your own wood it must be dried before it can be burnt. Typically, drying or seasoning wood can take 18 months.
Installing a wood burning stove may not be at the heart of the government’s heating strategy, but it can enhance the heating of any home. It can complement a heat pump, and provide heat security in severe winters.
Dennis Milligan is vice president of the BFCMA