Specifications

The ash pan needs to be emptied on a regular basis. The frequency will depend on the boiler type, the
fuel and also the amount of time the boiler is used. Wood ash can be used in the garden but care must
be taken that the ash contains no toxic elements.
Controls – control of any boiler system is crucial to the ecient operation of the system. A wood
boiler is no dierent – many higher quality boilers come with integrated control panels that are able to
enhance the eciency of the system. Characteristics of a best practice control system include:
Zoning of the heated spaces, for example living and sleeping areas*
Separate zone for the hot water tank*
Thermostatic control of space heating and hot water (i.e. boiler interlock to prevent the boiler ring
up when no heat is demanded from the hot water or space heating zones
Weather compensation
Delayed start thermostats or optimisers
Multi-channel controller capable of setting on-o times for each zone independently
End-user time and temperature strategy for the week (this depends on the occupancy patterns of
the homeowners)
*Note: See section 1.4.3 of the Technical guidance document of Part L of the 2008 Building Regulations for
guidance on “zoning” of a dwelling.
Heat Storage
For boilers without automatic ignition, for example wood log boilers that would burn a chamber of fuel in
a single burning period, it is important that the heat is used eciently. The heat must therefore be stored
somewhere so that it is available when required. A buer (or accumulator) tank is a heat storage vessel that
is connected to the boiler for this purpose. The buer tank is then connected to the heating and hot water
systems in the dwelling.
Some technical considerations include:
Compared to oil or gas, wood boilers take a little longer to start up and shut down, for example ve to
10 minutes. Boilers do not operate as eciently during start up and shut down. By using a buer tank
the number of start ups and shut downs is considerably reduced thus increasing eciency. Some wood
pellet boilers can vary their heat output to match the heat demand of the dwelling, so a buer tank
might not be necessary in these situations.
A buer tank eectively increases the heat load the boiler can cope with for example a 10 kW boiler
can cope with the design heat loads of a 13 kW boiler. This is because the heat can be stored up over
a relatively long period of time. As the name suggests, the tank “buers” the system against peak
demands. In a direct acting system the boiler needs to be capable of dealing with all demand at the
same time, for example heating and sudden demand for hot water.
As the buer tank needs to maintain temperature of the water over a long period of time, it should be well
insulated, for example 75mm–100mm of factory tted insulation.