Looking at the Government’s consultation on the proposed Future Homes Standard and also the Heat and Buildings Strategy, Dennis Milligan of the British Flue & Chimney Manufacturers Association says that it’s easy – but incorrect – to assume that there is no place for wood burning stoves and fireplaces in the homes of the future.
By 2025, the Government plans to introduce the Future Homes Standard for new build homes to be futureproofed with low carbon heating and world leading levels of energy efficiency, as part of the journey to achieve net zero by 2050.
The recent consultation set out what the government thinks a home built to the Future Homes Standard will be like. They want an average home built to the Standard to have 75-80% less carbon emissions than one built to current energy efficiency requirements (Approved Document L 2013). The plan is that this will be achieved through very high fabric standards and a low carbon heating system. The focus is on heat pumps, triple glazing and standards for walls, floors and roofs that significantly limit any heat loss.
A low carbon heating system will be integral to specification to the Future Homes Standard and the anticipation is that heat pumps will become the primary heating technology for new homes. BEIS is looking for sustainable low carbon heating solutions that can be rolled out across the country. Stoves are regarded as secondary heating and not scalable at the national level. For many homeowners stoves are a source of primary heating, particularly in the spring and autumn when it is not cold enough to justify turning on the central heating. Heat pumps work best when they are used in a steady state. Stoves can complement heat pumps as an efficient and sustainable way to boost heat quickly and give heat security in a cold snap.
BEIS is not opposed to wood burning stoves and believes that their use should be governed by Defra’s policy on emission limits. The Environment Act, published last year, sets out more stringent emission limits for wood burning stoves. All new appliances must now comply with the new efficiency and emission limits. There is always a proviso and that is appliances placed on the market for sale before 1st January, 2022 can still be sold. The new limit for particulate matter (PM) is 55% lower than for the previous Defra Exempt stoves, which were the gold standard for many years. The Stove Industry Alliance has initiated an independently verified scheme called Clear Skies. This scheme identifies stoves that not only meet the emission limits required by Defra but also stoves that produce fewer emissions. Increasingly stoves are becoming more efficient and are producing fewer emissions.
One of the ways in which stove manufacturers have reduced emissions is to retain the ‘products of combustion’ in the fire chamber for longer before releasing them into the flue. This needs to be factored into a chimney/flue design as this can reduce the velocity and temperature of the flue gases as they enter the flue. Most residential chimneys/flues rely on natural draft, the pressure difference between cold and hot air, to draw the flue gases up the chimney to the atmosphere. A potential reduction in velocity and temperature could reduce the draw of the chimney or flue. 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. The angle of the bends should be no greater than 45° from
the vertical.
The lower emission limits could spell the end of the traditional open fire. It has been common practice to include 200 mm flues and a standard fire opening in detached houses, leaving the choice of the appliance to the homeowner. Wood burning stoves require a smaller flue diameter, typically 150 mm. Installing a smaller diameter flue also has the benefit of substantially reducing the air loss calculated in SAP. The general opinion is that new open fires will not be able to meet the new emission limits. HETAS, the largest competent persons scheme provider for solid fuel, have advised their installers to check the emissions test results before installing a new open fire.
The current and future versions of SAP do not include secondary heating in the ‘notional building.’ This does not mean that a stove with a chimney/flue cannot be added to the house design and as already mentioned using a smaller diameter will significantly reduce the air loss calculation.
Work is continuing at a pace on replacing natural gas with hydrogen. It will be 2030 before a final decision will be made. In the meantime, a mix of 20% hydrogen and 80% natural gas is being trailed. The good news is that the network including flues can handle this without modification. Moving the percentage of hydrogen beyond 20% will require flues to be tested and certified for use. Work has already started on this in the development of product standards.
Wood burning stoves continue to be popular with house buyers and the steps that are being taken to improve efficiency and lower emissions should mean that they are fit for future use. They may not be officially part of the Government’s strategy for heating future homes but they can still be part of that equation.
Dennis Milligan is president of the BFCMA