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What is a Biomass Boiler Heating System?

Becky Mckay
By: Becky Mckay
Updated: 10th August 2023

biomass boiler heating systems
Biomass systems are combination of our earliest heating systems with modern day technology; they heat homes by burning various types of wood and natural materials rather than fossil fuels like gas or oil.

What is biomass fuel?

Biomass boilers are an alternative to gas and oil, burning wood to heat homes. In domestic settings, biomass fuel is made up of 3 different types of wood; pellets, chips or logs but it can also include biological material from plants and plant-based organisms.

Burning wood rather than gas or oil is much more sustainable as we can plant and grow new trees but we can't replace the gas or oil we're currently burning for fuel without waiting a few million years.

Wood pellets

The most popular fuel for biomass boilers is wood pellets which are made up of compacted sawdust and wood shavings. Thanks to their size, they're easier to transport and store than wood chips or logs and they can be automatically fed to the burner through a hopper, which means they don't require as much manual work.

If you're looking to make your biomass boiler as efficient as possible then wood pellets are the best choice out of the 3 as they have a higher calorific content.

Wood chips

Wood chips come from logs that have been passed through wood chipping machines and are cheaper to buy than wood pellets as they're much simpler to produce.

While they may be cheaper than wood pellets, they do have their disadvantages as they take up more space, making them harder to store, and their size increases the cost of transportation so expect fairly large delivery fees. Wood chips also have a higher moisture content than wood pellets which will have an impact on the heat being generated.

Wood logs

If you have access to waste wood at home or in the surrounding area then it's well worth considering a biomass boiler that can be fuelled by logs. Doing so could dramatically reduce your fuel costs or even remove them completely. It's worth bearing in mind that not all biomass boilers can be fuelled by wood logs so it's important to check you get the right model.

You will need a lot of logs to keep a whole home warm so having somewhere to store them is essential. As wood logs are fairly large, they can't be fed into a boiler automatically, so this job will have to be done manually.

How does a biomass boiler work?

A biomass boiler does exactly the same job as more conventional gas and oil boilers of heating the water supplied to your radiators, baths and taps. It's just that rather than burning gas or oil, they burn wood.

A gas boiler will be automatically fed gas from the mains but a biomass boiler needs to be topped up manually or via an automatic mechanism called a hopper. Having to keep filling the boiler with fuel yourself isn't exactly ideal so a hopper will take away this job, storing a large amount of fuel and then automatically refuelling the boiler as and when needed.

While a hopper will save you the job of filling the boiler, it can't empty all of the ash which will have to be manually cleaned out from time to time.

Note: Biomass boilers may burn a carbon neutral fuel but they can still produce carbon monoxide so you should still have a carbon monoxide detector installed nearby.

Why choose biomass?

The boilers in the vast majority of homes are fuelled by either gas or oil which may work well in terms of providing heat but they do emit carbon dioxide into the atmosphere. Burning wood is an alternative way of heating your home and, unlike gas or oil, it's a carbon neutral process. This is because trees are absorbing carbon dioxide as they grow, then when the wood is burnt, it only releases that very same carbon dioxide.

As well as being carbon neutral, wood is a much more sustainable fuel than the likes of coal, as it doesn't take millions of years to form.

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Why does wood chip moisture matter?

The amount of moisture within the wood you're burning will greatly affect the amount of heating being generated for your home. The higher the moisture content of the wood the less efficient it will be. Moisture within a piece of wood is determined by several things such as the weather, time of year and species of tree.

Wood chips that are too low in moisture will burn too quickly while wood chips containing too much moisture could cause the boiler to stop working. Moisture content is measured with a percentage and tends to range from about 25-60%, normally sitting at around 35%

How efficient is a biomass boiler?

In terms of energy usage, biomass boilers are just as efficient as a gas, oil or electric boiler with an efficiency rating of around 88-91%. So for every £1 you spend on energy, only 9-12p is being wasted.

How to maintain a biomass boiler

It could be easy to think that biomass boilers require lots of maintenance but that's only really the case with the manual models as they require regular checking and cleaning. You'll need to be aware of the ash level which needs emptying almost weekly and the fuel will need topping up every few days.

Automated boilers, on the other hand, don't require the same level of maintenance as they're able to self-clean and refuel via the hopper.

As is the case with any boiler, it's highly recommended to have an annual service by a qualified professional to ensure its running safely and efficiently.

Is a biomass boiler right for your home?

A biomass boiler is likely to take up more space in your home than a gas, oil or electric boiler and you'll not only need space for the appliance but somewhere to store the fuel too. Smaller systems are available, but these are hand-fed and fuel will need to be added more regularly so you'll need to consider whether this is feasible before investing.

In terms of the fuel, you will need plenty of storage space and may even require easy access for delivery trucks. To save space, many homeowners choose to store their fuel in a garage or an outdoor space protected from the weather to keep it dry, which is essential.

Your home will also need to have a high chimney that's suitable for wood burning. You may be able to convert an existing chimney by adding the right flue materials but this is likely to add to the initial costs.

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Biomass Boilers: Advantages & Disadvantages

See if biomass could bring more benefits to your home than an electric, gas or oil boiler.

Find out more


Becky Mckay

About the author

Becky Mckay

Becky has been a writer at Boiler Guide since 2021. Her vast boiler knowledge means she’s ready to help with any home heating query, big or small!

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