Specifications
The size of the buer cylinder depends on the capacity of the boiler. It is recommended that for every
kiloWatt (kW) of boiler power output you have 55 litres of buer cylinder storage. For example for a 15 kW
wood log gasication boiler, the recommended buer tank size would be approximately 15 kW x 55 = 825
litres. Manufacturers / suppliers may recommend a variation on these numbers depending on the system.
Burn back Protection
Burn back refers to the spread of re back through the fuel line and into the fuel store. This phenomenon is a
risk (if no prevention measures are in place) in boilers with auger fed fuel (most commonly chip and pellet).
Burn back protection refers to measures put in place between the fuel store and the burn chamber to prevent
a re spreading between the two areas.
Higher quality systems would often use two or three devices to ensure a high degree of safety. There are two
main types of measure to prevent burnback:
Physical measures
Interruption such as a “drop” (see below)
Shutters - these clamp shut and block the re path
Rotary pocket feeders - similar to a revolving door principle highlighted below
“Designed to fail” measures
Melting tubes - designed to melt in the event of re spreading through the fuel line (see below)
Water dousing systems in the fuel feed line and fuel store (designed to quench re)
All boiler systems have temperature limit thermostats which act as a rst line of defence against burnback.
However, these limit thermostats on their own do not provide sucient protection against burn back.
Wood boiler (left) and buer tank (right)