Wood fuel heating systems are best suited to providing a continuous heat load and burn most cleanly and efficiently when working at their maximum output. Therefore, it is best not to over-specify a wood fuel boiler but to choose one which is sized to meet your average heating requirements with additional heating sources to provide extra heat on the coldest days.
A good way to achieve optimum firing is to use an accumulator tank which allows the boiler to operate at maximum output to heat a large reservoir of water that is stored in an insulated container until required.
Unlike oil and gas, wood, in whatever form, does not achieve an optimum burn instantaneously and wood fuel boilers are not designed to continually cycle on and off. Therefore, if a continuous, low-level heat output is routinely required biomass may be the best choice.