Wood pellet boilers

What are wood pellets?

Wood pellets are a biomass fuel made from compressed sawdust, produced as a waste product from sawmills and used in wood pellet burners. Their shape is achieved by compression at the pellet processing plant and their shiny surface is from the natural glues found in the sawdust. As well as the significant environmental benefits, wood pellets are also cheaper than the fossil fuel alternatives for heating. More information on wood pellets can be found in our fuel section of the website.

What are wood pellet biomass boilers and why choose one?

Wood pellet biomass boilers are simply boilers that run solely on burning wood pellets and can provide all of your heating and hot water requirements. They are the most popular type in the UK and pellet heaters can be used effectively to heat domestic buildings all the way up to large factories. The vast majority of domestic installations will use wood pellet boilers. They are also the most popular type of commercial and industrial systems making up around 45% of those installed, with the next highest being wood chip that makes up around 40%.

Most modern wood pellet boilers will be over 90% efficient, sufficiently higher than most conventional fossil fuel systems which will typically be 70 to 80%. They are also far more environmentally friendly and burning wood pellets can significantly reduce your carbon emissions in comparison to using a fossil fuel alternative for heating e.g. a 3 bedroom home run on pellets will have CO2 emissions of just under a tonne a year if heated using pellets, in comparison to 4.5 tonnes if on mains gas, 6.5 tonnes if on oil, and 13 tonnes if heated by electric.

Much like wood chip systems, pellet boilers can also have a bulk fuel store which allows them to be automated so removes the day to day interaction that is required with log boilers which require frequent fills by the owner. In the majority of cases the main body of a wood pellet boiler where the combustion process takes place is almost identical to their wood chip counterparts. They do however differ greatly in the fuel delivery system that transports the fuel to the boiler and this offers them greater flexibility in terms of the positioning of equipment. Due to the bulk density and calorific value, a given volume of wood pellets will hold around 3.5 times the energy of the same volume that chip will give. This offers more flexibility to wood pellet heating systems once again as users can get away with much smaller fuel stores than they would be able to if they had a wood chip system.

Along with the potential for fuel savings, having a wood pellet heating system can make you eligible for the the governments Renewable Heat Incentive (RHI) which pays you to generate renewable heat for 20 years. These two combined can typically see the capital expenditure for a project paid back in around 5 years, with large gains then seen over the remaining lifetime of the pellet boilers installation.

More information about biomass boilers can be found on our Biomass Boiler page.

Fuel feed delivery options

Manual feed

A small day hopper is attached to the pellet boiler which is large enough to hold a few days worth of fuel in winter when the usage is highest. When the hopper starts to run low on fuel, it is manually topped up by pouring 15kg bags of pellets in. For ease of use and to keep fuel costs down it is recommended that a pallet full of bags of pellets is ordered at a time, with these then stored within a short distance from the boiler to make life easier when it is time to fill the hopper. This setup has the smallest footprint of all the fuel delivery methods. These are typically only used in domestic properties, as the heating requirements in larger commercial ones is too high and would therefore require the small hopper to be filled far too often. One of the boilers we sell and install with this as an option is the Froling PE1 (7 to 35kW).

Suction system

Suction system - This is a feed delivery system that can be attached to a bulk fuel store, which is filled with pellets by a fuel company, so it removes the requirement for the customer to manually load the boiler. Much like with the manual feed option, there will be a day hopper attached to the boiler which holds an amount of pellets that is then fed into the boiler. Within the hopper there is a proximity sensor that monitors the fuel level, as well as a suction turbine. Suction tube runs from the day hopper of the boiler and connects it to the bulk fuel store. When the proximity sensor records low fuel level in the day hopper, the suction turbine is automatically switched on and pellets are sucked from the bulk store into the day hopper until it is full. If the bulk fuel store is a silo then the suction tube will connect straight on to the base. Purpose built fuel stores are also very common and in these cases multiple suction cups are placed along the floor of the store to allow pellets to be sucked from a wider area. One of the boilers we sell and install with this as an option is the Froling P4 (15 to 105kW).

Pellet auger

Pellet auger - In part this is very similar to the suction system, in that there is a day hopper with a proximity sensor and suction turbine. Suction tube then again runs from the hopper, but instead of connecting directly to the bulk pellet store it connects on to a pellet auger. The pellet auger is positioned on the floor of the fuel store and runs down its centre. Sloping walls are installed that run from the pellet auger at 45° and direct pellets to the auger. When the proximity sensor registers the fuel is low, a signal is sent that switches the auger and suction turbine on. The auger turns and takes pellets to one end of it which are then sucked into the day hopper. The three main types of boilers that we sell with this type of feed system is the Guntamatic Pro (175 to 250kW) and Biocom (50 to 100kW), as well as the Froling P4 (15 to 105kW) .

Auger agitator

Auger and agitator - Unlike the other three feed systems, this is a multi-fuel system that allows a boiler to use both wood pellet and wood chip, so provides an element of fuel flexibility should people wish to change what there system is run on. Much like the suction system and pellet auger, this is a bulk fuel system so does not need to be manually fed. Unlike the other fuel delivery systems discussed, there is no day hopper which stores a small amount of fuel immediately adjacent to the boiler. With this method there is an auger that runs straight from the boiler into the centre of the fuel store. There is then a hub in the centre of the fuel store with 2 arms that stretch across the diameter of the store which are called agitators. When the boiler has a requirement for fuel both the auger and the agitator arms turn, with the latter pushing the fuel into the auger which then takes it to the boiler. The boilers which we sell with this feed system are the Guntamatic Powerchip (50 to 100kW) and Pro (175 to 250kW), as well as the Froling T4 (24 to 150kW), TX (200 to 250kW), TI (350kW), Turbomat (150 to 500kW) and Lambdamat (750 to 1,500kW).

Examples of each of these type of fuel delivery systems is given below.

Our installations

With over a decade in the industry we have a wealth of experience having installed hundreds of wood pellet boilers ourselves, as well as supplying them to trade to other biomass boiler installers and supporting them with their design and installation work.

Projects we have worked on range in size from a 15kW domestic installations, upwards to a holiday park district heating scheme where a 1MW biomass system was installed with 3MW of LPG duty assist and over 7km of undergound heat main.

Below are some case studies for a selection of some of our pellet boiler installations:

• Tata Global Beverage - Tetley Tea
• Soho Member Club - Great Tew
• Teighnbridge District Council - Dawlish Leisure Centre
• Warwick Council - Sayers Court
• NHS - South Petherton Hospital
• Sandroyd School