The new Document Part L 1a gives a greater role for wood burning stoves in the overall heating of a house, writes Dennis Milligan of Schiedel Rite-Vent.
When government embarked on the journey to the goal of carbon zero, energy efficient buildings, it set milestones in place, when it would seek incremental changes in energy efficiency and the production of carbon dioxide; 2010 is the first milestone and the new version of Document Part L is seeking a 25 per cent improvement in performance. The use of renewable energy sources, like biomass, are more vital than ever if this improvement is to be achieved.

Part L 1a deals with new dwellings. The most significant development is the ability to use wood burning stoves as primary heating so long as the stove can heat more than one room. The new SAP 2009, which will apply initially to new homes, caters for the specification of more than one source of primary heating. A typical example could be two primary heating systems consisting of a condensing boiler, heat pump or pellet boiler, with a linked stove system responsible for say 30 per cent of the heat load of the house. This will allow a stove to provide a significant contribution to the renewable energy sources of the house, while providing many house owners with the aesthetic feel they want their house to have.

It is in the self-build sector that homeowners have the final say in what goes into their houses and it is in this sector that most people choose to have a biomass appliance. Historically this was an open fire but increasingly it is becoming a wood burning stove, because of the higher efficiencies and low carbon output of wood burning stoves.

In recent years, when the cost of oil and gas was spiralling upwards many home owners were turning to linked stove and boiler systems to reduce their heating costs. Stove manufacturers have reported stoves with an integral boiler is the fastest growing product sector. The changes in Part L should give greater momentum to this trend.

There is no longer a requirement to specify secondary heating in a house if the house can be heated adequately with the primary heating source. When secondary heating is specified it accounts for 10 per cent of the overall heating of the house, if the house is on the gas main and 20 per cent if it is in an area without natural gas. Secondary heating is defined as a room heater, so a stand-alone stove can also contribute to the efficiency of heating the house and lower the CO₂ emissions in this way.

Fundamental to an energy efficient house is the need to retain air that has been heated. Traditionally stoves have taken their combustion air from the room so the SAP software calculates that the air loss is 20m³ per hour. However, room-sealed stoves draw combustion air from outside the house and chimney systems like the Schiedel Swift Air that can deliver the air directly to the appliance are now appearing on the market. The Schiedel Swift Air combines a well-insulated chimney shaft with an air duct that channels the combustion air directly to the stove. As no air is taken from the room the air loss for SAP is zero. From the view point of ventilation, it is as if there was no chimney in the house. The Schiedel Swift Air is suitable for all bio mass appliances - stoves, inserts and boilers.

Document L was published in April and will come into effect in England and Wales in October 2010. Sap 2009 will then be used to calculate the efficiency and CO₂ output of new dwellings. Existing houses will continue to be accessed using the current SAP 2005.