Heating with biomass
alive or dead at the time of harvest, it will take up to two years to air-dry the wood to below 20% moisture content. You will need to have space for three piles of wood: ready for this year, ready next year and ready the year after.
Biomass boilers qualify for the renewable heat incentive (RHI), the government scheme whereby those with renewable heating technologies are paid back for the heat they generate (normal rules around MSc accreditation apply). As do wood pellet fuelled stoves or stove-boilers. Log burning stoves do not qualify.
The current tariff is 6.74p/kWh and might only be considered as a bonus. If we assume a heating demand of 20,000kWh per year – about the minimum for a biomass boiler – the running cost would be around £1,200 per year with an RHI return of around £1,350 per year. This is a ‘profit’ of around £150 per year for seven years. But gaining that ‘profit’ will require an investment in excess of £10,000 for the boiler. A wood pellet stove-boiler could be as little as £2,000 and would return the same ‘profit’. An oil boiler, by comparison, might cost £5,000 including an oil storage tank, and will cost around £1,100 per year to run (for now) — obviously with no RHI return.
hoW to choose a model choosing between a stove and a boiler is relatively straightforward. In situations with a lowish heat demand, a wood pellet stove boiler can be a good option but otherwise a stove has to be considered as highlight heating.
If a boiler is needed then choose the preferred fuel first. Economically there is little justification for a log boiler, unless you have an abundance of free or low-cost fuel available. (In the 20,000kWh situation outlined above, about seven tonnes would be needed each year — and adequate space to store this volume of wood.)
As to choosing the specific boiler, find a good installer. Biomass boilers tend to last more than 20 years. A good installer can be relied on to install it properly in the first place and to maintain it — and is highly likely to recommend and install a good boiler, too.