Biomass boilers and stoves

Biomass boilers and stoves

Biomass boilers are a direct alternative to gas boilers but are very unlikely to fit in the same space so will require some changes in your home. 

The carbon dioxide emitted when wood is burned will be the same quantity which was absorbed when the plant was growing, thus making the process sustainable. Other biomass fuels include animal, food and industrial waste and it’s worth looking into who can deliver biomass fuels to your location before deciding on a biomass boiler because it’s not always possible to find a secure supply of biomass throughout the UK. 

Biomass boilers and stoves do require regular cleaning to remove ash, although some have self-cleaning systems. Wood burning stove and boiler owners must ensure that the chimney and flue pipes are swept professionally each year.

Biomass boilers are larger than gas or oil equivalents. You will also need space to store the fuel and a flue which complies with regulations – either an existing lined chimney or a new insulated stainless-steel pipe. All new wood heating systems have to comply with building regulations, so it’s best to check with your local planning authority to find out if planning permission is required. Although set up costs can be pricey, biomass boilers are superb alternatives to gas boilers and offer returns that more than justify the initial expense.

How do biomass boilers work?

Biomass boilers burn wood pellets, chips or logs to provide warmth in a single room or to power central heating and hot water systems. A biomass stove burns logs or pellets to heat a single room and may be fitted with a ‘back boiler’ to provide water heating as well. The heated water from a biomass boiler or stove with a back boiler is then circulated around an underfloor heating system or conventional radiator system to heat the home.

biomass boiler diagram

Biomass boilers efficiency

Burning wood is not a very efficient process as it is hard to avoid a lot of the heat disappearing up the chimney. However, wood burning stoves are far more efficient than an open fire because they heat the metal box containing the fire which then radiates heat into the room. Biomass boilers which burn wood pellets are another step up in efficiency again and are probably the most efficient form of wood burner for the home. Some pellet boilers claim 80 to 90% efficiency, but we have yet to see empirical evidence for these claims.

Advantages

Biomass is sustainable

The main advantage of a biomass boiler is that it offers a sustainable form of heating that can provide an entire home’s heating or hot water without requiring gas or oil. If you can’t or don’t want to use renewable electricity to heat your home, biomass is pretty much the only other option, apart from solar thermal, which is unlikely to meet your heating demands in the winter.

Biomass can be sourced from multiple suppliers

Biomass can, in theory, come from many different sources, in the form of logs, wood chips, and pellets made from sawdust – and since there are several different suppliers of these fuels, using biomass to heat your home and hot water will not lock you in to one supplier. However, we have found in practice that it can be hard to secure biomass fuel, and to get it where you need it on the date you need it, which is not very practical.

Escape the Big Six

It might sound a bit Orwelian but with gas and electricity you really are locked into ‘the system’. You can choose who supplies you but not much else and you will simply have to put up with deals you are offered and whatever price rises global politics and war dictate. With biomass however, you’re free of all that. OK, the price of biomass may vary but you are not locked into the national energy grid and are therefore much more independent. If you have your own source of biomass fuel the advantages of switching to biomass heating are considerable.

Biomass boilers work with conventional radiators

Another advantage of switching to a biomass boiler is that it may be compatible with your existing radiator system so, unlike with ground or air source heat pumps, you are less likely to need to completely reconfigure your heating system.

Disadvantages

High upfront costs

Biomass boilers have a high upfront cost, similar to a ground source heat pump. The final price will vary based on your specific circumstances but don’t expect to switch to a biomass boiler system for much under £10,000 – and that’s after you’ve benefited from the £5,000 available from the boiler upgrade scheme.

Biomass pellet boilers can be noisy

It’s not a major drawback but it is worth recognising that pellet boilers, which use self-loading systems to deposit pellets into the burning chamber and motors to drive fans, are not silent – in fact, they probably make more noise than a gas boiler. 

Biomass boilers require regular maintenance

Like any system with moving parts a biomass boiler will need regular maintenance, especially systems which use archimedes screws to lift pellets from a store and drop them into a hopper. In our experience, although these systems sound great, they invariably go wrong or get stuck and will need some regular TLC. Biomass boilers and flues also need cleaning which, if you don’t want to do yourself, will be an additional cost.

Biomass pellet boilers use electricity too

This point only applies to pellet boilers with fans, electric controls and pellet feeders, not wood burning stoves, but it is worth mentioning because, if your biomass boiler does use electricity it will not work in a power cut. The cost of the electricity is practically negligible for any biomass boiler (unlike for ground or air source heating) and will rarely be more than a tiny fraction of your annual bill, but the reliability issue is real. If you don’t have backup power it is very frustrating to lose your biomass heating when the electricity goes off – after all, the whole point of biomass is that it frees you from being reliant on the power grid and power companies.

Biomass availability and fuel price can vary

Transporting biomass is costly, and normally requires a diesel truck. So this aspect of biomass heating is definitely not zero carbon, unless your pellets arrive in an electric or biodiesel powered vehicle. Transportation also makes up a significant part of the cost of the fuel so, depending on where you live, this can make biomass prohibitively expensive. If you live in an area without much biomass you will end up paying to have it brought to you, or to collect it.

Biomass fuel requires space

You will need somewhere to store your biomass fuel – either a log shed or a purpose built hopper for pellets.

Space for a compliant flue

A biomass boiler must also have a flue that meets the regulations. These can be fitted inside an existing chimney but in most situations this will mean a big fat shiny pipe running up the outside of your house, all the way to above the gutters.

Biomass boilers costs

Biomass boilers and stoves are not cheap – and costs vary considerably depending on what you choose and how much additional installation work is required for the flu and integration with your radiators or underfloor heating system. It is possible to buy a basic wood burning stove from as little as £600 but this will not be a suitable replacement for gas central heating as it will only heat one room and not hot water.

If you’re looking for a biomass boiler to replace a gas boiler and which will provide you with heating and hot water all year around the cost will be between £14,000 and £20,000 for an average 3 bed home.

Fuel prices can also vary considerably – having practically doubled in the last year! At the time of writing in early 2023 you can expect to pay the guide prices below for a tonne of the different types of biomass:

  • Wood chips £200 / tonne
  • Logs £400 / tonne
  • Pellets    £600 / tonne

On average, a tonne of wood pellets produces around 4,800kWh of heat. This means that it will take around two to three tonnes of pellets to heat an average 3 bed home throughout the year. But, if your home is big or poorly insulated, you will end up burning more than this to stay warm.

Is a biomass boiler worth it?

If you have your own source of biomass fuel then switching from any other form of heating to biomass is definitely worth it. If you don’t have a free supply of biomass then it’s a hard decision. Without a reliable fuel source at predictable prices it’s hard to feel confident that you will always be able to heat your home at an affordable price with biomass. Recent price rises have made logs and pellets so much more expensive that it is now not cheaper to use biomass than gas. The Energy Saving Trust states that if you currently have a modern condensing gas boiler, a biomass boiler is likely to cost you more to run than your current system.

Biomass boilers are eligible for the Boiler Upgrade Scheme, to the tune of £5000, so the final installation cost will be less than the price quoted by the supplier. And let’s not forget that biomass (if it is not brought to you using fossil fuels) is carbon-neutral, so has significant advantages over gas. 

To find an accredited installer in your area, pick one that is part of the Microgeneration Certification Scheme from the list on the MCS website.

Check out the other alternatives to gas boilers in our energy guide.