There are many forms of biomass. This document covers wood chips and pellets for use in boilers in commercial developments. The application of wood-fired boilers to building developments, where there is a significant space heating or domestic hot water demand, offers the possibility of considerable reductions in carbon dioxide emissions, generally greater than any other currently available on-site renewable technology. This document covers biomass installations that could satisfy a peak heating demand of between about 50 kW and 5000 kW with operation of the boiler assumed to be essentially automatic, i.e. a viable alternative to gas-fired plant in a modern commercial development. For 30 years or more, natural gas-fired boilers have been the preferred choice of most building services engineers and most engineers are familiar with the design of gas-fired systems. The design of wood-burning boiler installations is very different. Combined heat and power (CHP) fired by biomass is also an emerging renewable energy source for buildings. This is briefly discussed in that it can utilise wood as a fuel. --