Biomass Heating - Is it suitable for everyone?

Choosing Biomass as a heating solution which requires careful consideration for a number of reasons; Firstly is it sustainable? Building with trees and subsequently locking up the embodied carbon for 60 plus years is far better than releasing it into the atmosphere through burning, so what makes biomass sustainable? Scale is the key, building biomass power stations and importing wood stock from around the world and using UK wood destined for sheet material production (for example OSB in Scotland) to generate electrical power is relatively inefficient once you allow for grid losses and isn’t that sustainable. However, domestic scale heating at the point of use and located in areas near woodland can help stimulate micro businesses managing woodland that might have been uneconomic without the demand for logs. The production of pellets & chip from wood waste could also be putting recycled timber to good use.

Wood fired heating of an autonomous house can be sustainable if the fuel is harvested on site, assuming the house is low energy and the burner is active (over 90% efficient). This, in combination with on site electrical generation by wind, solar PV, hydro etc would eliminate the need for importing energy to site and is probably the ambition of many eco-self sufficiency people such as me! But the real key is limit the need; Make sure your building is as energy efficient as possible, ideally to passive  house (passiv Haus) standards. If you can then your heat load & running costs through the year will be minimal. Putting a biomass boiler into a typical semi-detached house in town and buying ready dried logs will cost more to run than a condensing boiler and take up time every day in loading, so it certainly doesn’t suit everyone and every location. It is best suited to remote housing farms and small businesses near woodland. A perfect example is Kent where there are many acres of chestnut coppice which have been uneconomic to manage since the downturn in the wood pulp market following the closure of large paper mills. Managing chestnut coppice is now becoming more viable with an increase in use of wood fired heating.

In terms of buying logs it’s best to assume they are too wet to burn until you’ve owned them for at least a year. If you haven’t got adequate storage space to hold up to 2 years worth of logs on site, then consider kiln dried wood as long as it’s been dried as secondary activity, ie saw mill offcuts, or where the heat to operate the kiln is waste energy from another activity or best of all from a solar kiln, dried by the power of the sun, for example in poly-tunnels with vented sides. Which ever solution you choose, make sure your logs are near to 15% moisture content as the higher the moisture content the lower the amount of heat the fuel will generate and excessive moisture in burners and flues can shorten their design life significantly. As a general rule if you cannot rely upon the moisture content in your fuel then buy a basic wood boiler that will be less susceptible to moisture, although you will get through a lot more wood, you can load it with a greater variety of timbers including pallets but avoid painted or treated wood as they will give off harmful toxins. If you can ensure your fuel supply is very dry then an active wood burner, ie a fan assisted solution, makes more sense as you will get through a lot less wood and generate more heat (over 90% efficiencies).

Pellets should to be dry enough from source but it’s worth trying a few suppliers to work out which burn best as some have higher moisture content and as a result the pellet boilers don’t achieve their optimum output. Storage tends to be less of an issue because the drying process should have occurred off site so this makes more sense for homeowners with limited storage space.

Wood Chip boilers are an ideal solution for farm scale or small community heating schemes as the process can be automated like pellet, but be cheaper to run, however controlling the moisture content can be more difficult so the efficiencies can vary.

For optimal use, you also need a Thermal Storage Tank so that the hot water you produce from whichever boiler you choose can be stored for later use. You also need to think about where you are going to install the Thermal Storage Tank and how you are going to get them into the area as they can be wider than a normal door opening. In summary, don’t just research biomass boilers. Do your homework on your fuel, size of room and access point as it could cost you dearly in the long run if you get it wrong.