Before switching to any new heating system it is vital to maximise energy efficiency. Measures such as increasing insulation, lagging pipes and draught-proofing will save money on fuel, and also on equipment - as they’ll allow you to specify a smaller boiler. A combination of wood fuel and solar water heating (for hot water in summer), can give renewably-generated heat all year round.
Open fires are a poor choice, financially and environmentally, as they are incredibly inefficient. A simple wood stove is a great improvement; it should need only one-third as much fuel.
Automated pellet stoves are more convenient, and can even have an automatic de-ashing function.
Advanced wood heating systems for larger houses have been common for many years in mainland Europe and the USA, and are as efficient as modern gas boilers - converting well over 80% of the fuel into useful heat.
A ‘batch’ log boiler can be loaded and fired up with logs once a day (or less often) and the heat stored in a large water cylinder called a buffer store or accumulator tank.
Automated pellet boilers make wood fuel almost as convenient as gas. They are more costly, but ease of use is a big plus.
Woodchip boilers tend to be larger and so suitable for groups of domestic dwellings, public buildings and so on.
There are specially designed wood-fired ranges that you can also cook on, but these are less efficient.
Buffer / accumulator tanks:
If your house has underfloor heating, then the buffer tank can be smaller, as you only need to supply water at maybe 30 or 35 degrees C. But if you have radiators that need a high temperature of water, the buffer tank needs to be larger to keep enough water above 50 degrees. The specific size of tank will depend on various factors. A pellet boiler will also benefit from a buffer tank, but the requirement is smaller – maybe only 600 litres. This will enable you to run the pellet boiler flat-out for a longer period, to get the most efficient combustion.
See also: How can I find a wood biomass installer?