Uppermost in the requirements for modern heating systems are energy efficiency and low carbon emissions.
Wood burning stoves meet both criteria and these efficient stoves can help householders meet the current and future energy efficiency requirements.
Wood Logs as Fuel
Wood is one of the most environmentally friendly fuels that can be used. It is a sustainable renewable energy and virtually carbon neutral.
The natural cycle of planting and harvesting trees has created a sustainable process that will provide carbon neutral solid fuel far into the future. CO2
is taken out of the atmosphere by growing trees at the same time as it is released by the combustion of the previous harvest. To reflect this closed loop CO2
cycle the carbon factor for wood logs in the official software used to measure the energy efficiency of homes (SAP) is 0.008kg of carbon per kwatt compared with 0.198kg for gas, 0.274kg for oil and 0.517kg for electricity.
Stoves as secondary heating
Many people choose to have a room heater to provide heating when the outside temperatures don’t justify the use of the central heating system or to create a focal point in a living room.
Until now, the most popular forms of room heating have been open fires or room open gas effect fires. Neither room heater is particularly efficient. An open fire has an efficiency of 32% and a room open gas effect fire in the region of 55%. The low efficiency with the carbon content of the fuel increasingly makes these options difficult to install in an energy efficient house. A wood burning stove ticks all the energy efficiency & carbon saving boxes. The average efficiency of a modern efficient stove is in excess of 70% with the more efficient stoves achieving 80% plus. This level of efficiency combined with the low CO2
output makes wood burning stoves very environmentally friendly.
When secondary heating is specified it accounts for 10% of the overall heating of the house, if the house is on the gas main and 20% if the house is in an area without natural gas.
Stoves as primary heating
One of the most significant developments in Document L is the ability to use a wood burning stove as primary heating so long as the stove can heat more than one room.
The SAP energy efficiency software caters for the specification of more than one source of primary heating.
A typical example could be 2 primary heating systems consisting of a condensing boiler, heat pump or pellet boiler, with a linked stove system responsible for heating the living rooms.
This will allow a wood burning stove to provide a significant contribution to the renewable energy sources of the house, while providing house owners with the aesthetic feel they want their house to have.
An oil boiler, for example, will struggle to meet the carbon output requirements of SAP and will need to rely on other features of the house to meet the SAP requirements.
The low level of CO2
produced by burning wood makes a wood burning stove an ideal and affordable method of doing this.
The chimney plays an important role in the heating system as an efficient heating appliance requires a well and consistently insulated chimney to perform efficiently.
Chimneys are available in a range of materials. Clay and concrete liner systems require insulation to be fitted at the time of installation.
Prefabricated chimney systems in stainless steel, pumice and clay include the insulation as part of the system. Stainless steel tends to be used in existing houses because it is light-weight and does not require a specially constructed foundation.
A new chimney can be easily installed in a house that does not have one and an existing chimney can be relined with flexible stainless steel to create a suitably sized flue for a stove.
Further information on chimneys & flues can be found on the BFCMA (British Flue & Chimney Manufacturers Association) web site www.bfcma.co.uk
SAP is the Standard Assessment Procedure used to calculate the overall energy efficiency and carbon output of a house.
The program produces a single value for the energy efficiency of the house and for the amount of CO2
given out. The energy efficiency and CO2
output of the components of the house are combined to produce an overall result for the house.
A more efficient or less carbon intensive component can be used to compensate for a less efficient/more carbon intensive one.
This method of 'carbon trading' within the house means that a less carbon intensive appliance like a wood burning stove can be used to compensate for a more carbon intensive appliance.