68 HEATING, VENTILATION & SERVICES


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  is  lower than for the previous Defra Exempt stoves, which were the gold standard for many years. The tove ndustry lliance has initiated an independently verifi ed scheme called Clear Skies. This scheme identifi es stoves that not only meet the emission limits reuired by efra but also stoves that produce fewer emissions. Increasingly stoves are becoming more effi cient 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 fi re chamber for longer before releasing them into the fl ue. This needs to be factored into a chimneyfl ue design as this can reduce the velocity and temper- ature of the fl ue gases as they enter the fl ue. ost residential chimneysfl ues rely on natural draft, the pressure difference between cold and hot air, to draw the fl ue gases up the chimney to the atmosphere.  potential reduction in velocity and temperature could reduce the draw of the chimney or fl ue.  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 fi re. t has been common practice to include 200 mm fl ues and a standard fi re opening in detached houses, leaving the choice of the appliance to the homeowner. Wood burning stoves reuire a smaller fl ue diameter, typically 150 mm. Installing a smaller diameter fl ue also has the benefi t of substantially reducing the air loss calculated in . The general opinion is that new open fi res will not be able to meet the new emission limits. ET, the largest competent persons scheme provider for solid fuel, have advised their installers to check the emissions test results before installing a new open fi re. The current and future versions of  do not include secondary heating in the ‘notional building.’ This does not mean that a stove with a chimneyfl ue cannot be added to the house design and as already mentioned using a smaller diameter will signifi cantly reduce the air loss calculation. Work is continuing at a pace on replacing natural gas with hydrogen. It will be  before a fi nal decision will be made. In the meantime, a mix of 20%


STOVES CAN COMPLEMENT HEAT PUMPS AS AN EFFICIENT AND SUSTAINABLE WAY TO BOOST HEAT QUICKLY AND GIVE HEAT SECURITY IN A COLD SNAP


hydrogen and 80% natural gas is being trailed. The good news is that the network including fl ues can handle this without modifi cation. oving the percentage of hydrogen beyond  will reuire fl ues to be tested and certifi ed for use. ork has already started on this in the develop- ment of product standards. Wood burning stoves continue to be popular with house buyers and the steps that are being taken to improve effi ciency and lower emissions should mean that they are fi t for future use. They may not be offi cially part of the overnment’s strategy for heating future homes but they can still be part of that euation.


Dennis Milligan is president of the BFCMA


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