What is a Biomass Boiler?

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Last updated: October 31, 2023

Biomass boilers burn a sustainable, renewable and carbon-neutral fuel in the form of recycled or directly felled wood. While burning wood logs, pellets and chips may seem like an ancient and perhaps outdated way of producing heat, it is still the most reliable, and surprisingly to some, one of the most eco-friendly ways of heating. Available in various models and sizes, biomass boilers can meet the heating needs of most homes and businesses. Despite all this, there is quite a bit of confusion around biomass boilers, especially with questions about whether they’re truly cost-effective and environmentally-friendly. To dispel myths and confusion around biomass boilers and help you decide if this is the right type of heating for your home, we’ve put together this comprehensive guide to biomass boilers. Here, we cover everything you need to know about wood boilers, including exactly how they work, what types of fuel they can use, how much they cost, and more.

What Is a Biomass Boiler?

A biomass boiler is similar to a gas boiler or oil boiler, as it provides heating and hot water for the entire home by burning fuel. However, instead of burning fossil fuel like oil and gas boilers do, a biomass boiler burns organic matter, also known as ‘biomass’ (hence the name), which can come in the form of felled or recycled wood, as well as plant material.

Because a biomass boiler burns fuel that is obtained from natural, organic matter, it is more environmentally-friendly and sustainable than boilers that work on fossil fuels. This renewable heating system is available in several types, with capabilities and prices varying between each. We’ll go over each variation a bit later, but for now, suffice to say that biomass boilers are versatile, long-lasting and cost-effective. They’re a fantastic option for people looking for sustainable and renewable heating, as well as for homes with no mains gas supply.

How Do Biomass Boilers Work?

A biomass boiler works by burning biomass in its combustion chamber that is either being fed into it by hand or automatically. The hot gas and air produced then travel through a flue and are passed through a heat exchanger, which in turn transfers the heat to the water that is used in a property’s central heating system.

While biomass boilers work in a similar way to oil boilers, they are, of course, different. Unlike gas or oil boilers, these heating systems burn biomass fuel, which comes in the form of wood pellets, wood chips, logs and other plant material. Whatever kind of biomass fuel is intended for your specific heating system, your boiler will have to be fed that fuel either manually or automatically on a regular basis. Whether you choose to purchase an automatically fed boiler or a manually fed one, the great news is that there is relatively little maintenance necessary for your biomass heating system to function aside from cleaning the boiler and removing the built-up ash every once in a while. Depending on the technology of your boiler, this can be once every four weeks to twice a year. Of course, annually servicing your biomass boiler is also recommended.

If you choose to go down the automatic feeding route (which most folks do as it’s more efficient and easier to use), you’ll need to install an automatic feed hopper, which requires an additional room. This automatic mechanism stores large amounts of biomass fuel which is automatically fed into the boiler as required. This means that you’ll have to top up the feed hopper very infrequently.

All in all, a modern biomass boiler can achieve an energy efficiency of around 90%, which is equivalent to the efficiency of both gas and oil boilers.

What Fuel Does a Biomass Boiler Use?

There are several fuel types that can be used in biomass boilers, including wood fuel and non-wood biomass. When thinking about which biomass boiler fuel will work best for your needs, it’s important to think not only about the costs of the fuel but also the logistics of sourcing it on a regular basis.

  • Wood chips

Wood chips are small pieces of logs and other wood waste. Simple to produce (wood is fed through wood chipping machines), wood chips are the cheapest type of biomass fuel (around 2.5p per kWh) that is best suited to medium and large boilers (50kW).

While very affordable, this type of wood fuel is not necessarily the best choice for a domestic boiler because it does take up quite a lot of space. Importantly, wood chips also have a pretty high moisture content (around 30%), which means that they should be used relatively quickly and not stored for long periods of time as they can begin to degrade. This is a problem because the degradation process causes something called the germination of fungal spores, which can cause serious health problems in humans. To be more precise, large quantities of these fungal spores can cause farmer’s lung disease, which is incurable. The good news is, even if you have to store your wood chips for longer periods of time, you can prevent microbial activity by agitating the wood chips often and keeping the storing room well-ventilated so they can dry.

  • Wood pellets

Wood pellets are made from sawdust, wood shavings and other waste material from wood manufacturing. Dry and dense, they are the most efficient form of biomass fuel (and a bit more expensive than chips at around 4p per kWh), and as a bonus, the easiest to store as well. Wood pellets are also uniform in size, meaning they’re perfect for automated pellet boilers as they can be automatically fed from the fuel store through a hopper, reducing the workload for you.

On the negative side, there are safety issues concerning the dust produced from wood pellets when they are being transferred through a hopper. To minimize dust, it’s advisable to use smooth pipes with a large radius, as well as a hopper with an installed impact baffle. This prevents the wood pellet from shattering upon entry, thus avoiding dust which can be a problem for people with respiratory issues and asthma. Another thing to keep in mind with wood pellets is that because they’re so dry, they’re also highly flammable. Great news for your pellet boiler, but can be dangerous if you happen to have open electrics near the hopper.

  • Logs

Logs are another type of wood fuel that can be used for some biomass boilers. They’re a good choice for people with access to waste wood (no fuel costs!) who also have larger properties as logs do require suitable storage space.

Like wood pellets chips, logs have a high moisture content, so they don’t make for a highly energy-efficient fuel. However, this can be remedied by seasoning: to remain as dry as possible, logs should be kept in a dry place for at least a year before they can be burnt. This is important not only because dry logs are much more energy-efficient, but also because damp logs produce smoke and tar when burnt. Another downside to wood logs is that they cannot be automatically fed into a log boiler by a hopper – you can only feed them by hand.

  • Plant material

Finally, plant material such as agricultural waste can also be used as fuel for some boilers. This typically includes straw and wheat husk, although other non-wood biomass can also be used in certain boilers, such as paper pulp.

While biomass boilers that run on non-wood biomass fuel are no that common, they can be a great choice for people looking to reduce their carbon footprint. Utilizing waste plant material for heating offers quite a few environmental benefits, including conservation of fossil fuel resources and emissions reduction. However, it should be noted that boilers that run on agricultural residues usually require daily topping up, which can be too much work for some.

Wood pellets

Different Types of Biomass Boilers?

There are a few types of biomass boilers available on the market, with varying costs, sizes and efficiencies.

  • Fully automated biomass boiler

These are the most efficient and easiest to use biomass boilers. In this type of boiler, wood – usually in the form of wood chip or wood pellet – is automatically thrown into the combustion chamber from a hopper. Fully automated boilers can keep a very large amount of biomass fuel in their holding tank, so topping them up is necessary only every once in a while. These boilers can be both industrial and domestic biomass boilers.

  • Semi-automated biomass boiler

Similar to fully automated boilers, except they require more work on your part to keep operational, semi-automated biomass boilers can also store relatively large amounts of fuel. Nowadays, semi-automatic domestic biomass boilers are compact in size as they are designed specifically for homes. For this reason, they don’t take up much space, plus they look good, making them highly popular among consumers. As for the industrial semi-automated biomass boilers, they’re much larger and are better suited to larger properties such as farms.

  • Combined heat and power biomass system

As the name suggests, combined heat and power (CHP) systems generate both heat and electricity by burning biomass. While extremely useful, CHP systems are very expensive, so they’re not suitable for domestic and small business properties. But for larger buildings and properties, they can be excellent. The great thing about the CHP biomass systems is that since they produce both heat and electricity, they may be eligible for Renewable Heat Incentive. For those unaware, the Renewable Heat Incentive scheme has been extended to run until 31 March 2022.

What Does a Biomass Boiler Cost?

Like a lot of boiler options out there, the cost of a biomass boiler can be tricky to pin down. This is because there are a lot of different biomass boilers available, including log boilers, wood pellet boilers, wood chip boilers, fully automatic, semi-automatic, domestic and industrial boilers. Of course, there are also different boiler sizes available, and there are installation costs to think about as well.

Roughly speaking, you can expect to pay anywhere between £14,000 and £19,000 for a domestic fully automatic pellet boiler, which includes installation costs. An individual pellet stove is cheaper, of course, ranging between £4,000 and £5,000. As for log boilers, the price ranges between around £11,000 and £23,000. In general, fully automatic and semi-automatic boilers cost more than manually-fed options. As for the costs of running a biomass boiler, they are centred around the fuel type you use.

It’s important to keep in mind that the installation costs vary widely, based on the installation company you hire, your location, the type of your boiler, and so on. So, when installing a biomass boiler, we highly suggest getting multiple boiler quotes.

Is a Biomass Boiler Right For My Home?

Biomass boilers are a great choice for people looking for renewable heating options. Unlike oil and gas, which are fossil fuels, biomass is a carbon-neutral and renewable energy source.

While chopping down trees in order to burn them for biomass heating may seem the opposite of eco-friendly, most of the felled wood is sustainably grown and replanted as soon as possible. In essence, carbon dioxide emissions from trees that are burned are cancelled out by the planting of new trees (if not completely offsetting the carbon dioxide emissions, this greatly helps reduce them). On top of that, tonnes upon tonnes of wood waste ends up in landfills each year, so burning it to heat homes takes the strain of the landfills as well.

This all said, biomass boilers are not suitable for every property as many types require quite a bit of space compared to standard fossil fuel boilers. So, flats and most small urban and suburban properties are simply not able to accommodate larger biomass boilers (however, some may be able to accommodate smaller semi-automated boilers).

For homes and businesses with plenty of space, however, these boilers can be fantastic heating options. They’re particularly attractive for properties that are not connected to a gas network.