Biostar: 12-23kW Biomass Boilers

The Guntamatic Biostar burns ENPlus A1 wood pellets.

Guntamatic: The Biostar Range

These highly efficient wood pellet boilers are capable of heat outputs of 12, 15 or 23kW. They can also be fitted without a buffer tank, which makes them the ideal choice for domestic installations and light commercial use where space is at a premium. We have installed several in the Wye Valley and further afield and customers have been delighted with the performance of this advanced system.

Every boiler in the range is RHI compliant and MCS accredited.

Seriously Low Emissions

The Biostar's emissions have been measured as significantly below the maximum emissions set out as a requirement for the RHI. The values of each model are in the table below and you can see the certificate here.

Boiler PM NOx

Maximum Emissions

30 g/GJ 150 g/GJ
Guntamatic Biostar 12 Emissions 8 82
Guntamatic Biostar 15 Emissions 14 82
Guntamatic Biostar 23 Emissions 19 90

Wood Pellets

The Biostar can hold up to 140 litres of wood pellets in the hopper attached to the boiler. This can run the Biostar for one to 3 days, depending on usage.

Stock up on ENPlus A1 pellets and these can be blown directly into a larger fuel store upon delivery. Your fuel store can be located up to 20m from your boiler and set up so that the pellets are fed into the 140 litre day hopper automatically by vacuum tube.

Automatic Ignition and Lambda Probe

These boilers are designed to achieve a quick and easy start with automatic hot air ignition and a lambda probe to add just the right amount of oxygen. The result is optimum combustion and optimum efficiency.


The Biostar features Guntamatic’s innovative self-cleaning system, where turbulators move constantly to keep heat exchanger tubes free from buildup of deposits.

Control Panel

Your Biostar boiler comes with a touch screen panel fitted as standard. This puts you in control and gives access to efficiency, fault and maintenance information. Plus, if you opt for the additional GSM module, you’ll be able to control the boiler’s settings from your smartphone.

Efficiency in Modulation

Biostar boilers are famed for their ability to maintain 96% efficiency between 26-100% of output. So you’ll enjoy maximum value for money through a more complete burn.

Low Ash Content

For the volume of fuel, just 0.5-1% ash is generated, meaning that you’ll only need to empty the 38 litre ash bin every six to eight weeks.

Fuel Delivery

The Biostar comes with the option of fitting a Flex fuel delivery system. This consists of a vacuum hose which connects your boiler to a custom-built fuel store (of any size) and feeds pellets into your boiler via an auger.

When planning your fuel store, evaluate your likely usage so that you can build a store that’s big enough. Ideally, you shouldn’t need to refill it more than three or four times a year.

Flexx plan view of fuel store

The outfeed auger is available in a variety of lengths up to 5.4m to fit your custom-built fuel store:

Flex Size Auger Length Options
Flex 1 1,080 – 1,559mm
Flex 1.5 1,560 – 2,039mm
Flex 2 2,040 - 2,519mm
Flex 2.5 2,520 -2,999mm
Flex 3 3,000 – 3,479mm
Flex 3.5 3,480 – 3,959mm
Flex 4 3,960 – 4,439mm
Flex 4.5 4.440 – 4,919mm
Flex 5 4.920 – 5,399mm

Prefabricated ‘Box’ Fuel Store

We also offer a prefabricated fuel store solution that’s suitable for keeping up to 9 tonnes of ENPlus A1 and A2 wood pellets. The storage box arrives flat-packed, has a stable, steel base, filling tubes, a suction coupling and it’s adjustable in height. Also supplied is a vacuum tube for feeding the pellets into the boiler.

The Box System Comes in Five Sizes:

Box Model Dimensions Fuel Capacity

Box 5.2

170 (w) x 170 (l) mm 2 - 3.4 tonnes 3 - 5.2m3
Box 7.5 210 (w) x 210 (l) mm 3 - 4.7 tonnes 5 - 7.5m3

Box 8.3

290 (w) x 170 (l) mm 4 - 5.4 tonnes 6.1 - 8.3m3

Box 11

250 (w) x 250 (l) mm 5 - 6.7 tonnes 8.3 - 11m3

Box 14

290 (w) x 290 (l) mm 6.5 - 9.1 tonnes 6.5 - 14.1m3

‘W’ fuel store

Another option for your Biostar boiler, the W is an integrated, 400-litre fuel store which can hold enough pellets to see a well-insulated building through for up to a month.

50 Years’ Experience Built In

Having recently hit their 50-year anniversary, it’s clear that Guntamatic are market leaders in renewable energy technology. Experience means that every boiler they make is created with huge industry expertise, and the Biostar is no exception.

Parts Available for 20 Years

Guntamatic are unique amongst biomass boiler manufacturers as they make all of their own structural components. Every single part of the Biocom is of the highest standards, offering you maximum return on your investment, low maintenance requirements and a long service life. You can get hold of spare parts easily as Guntamatic guarantees to make parts available for 20 years.

European Training Academy

They put an equal amount of effort into developing installers at their European Training Academy, so an authorised, highly trained and experienced engineer will fit the system for you.

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Biostar Technical Data 12 15 23 12W 15W
Min-Max Outputs (kW) 3.3-12 3.5-15 6.9-23 3.3-12 3.5-12
Shipping Weight 298 300 305 268 270
W Storage Capacity (Ltr)   400
W Storage Capacity (kg)   140
W Run Time, ine Fill/Day, 14 hours/day    7-21 6-21
Boiler Temperature oC 38-80
Minimum Flow Rate (Ltr/Hour) 600
Draught Requirement (mBar) 0.1



Wood Pellets

What are wood pellets?

Wood pellets are made from compacted sawdust or any other waste produced from sawmills and other manufacturers.

What is the calorific value of wood pellets?

It’s 4.8kWh per kg, meaning you only need one third of the storage space that you would need for chips. Plus you get three times as much heat.

  • Wood Chips = 250KG/m3
  • Wood Pellets = 650KG/m3
How much do I need, compared to oil?

1 litre of oil is equivalent to 2kg of wood pellets.

What is the cost of wood pellets?

You can expect to pay between £180 - £220 per tonne.

Where is the nearest supplier of wood pellets?

We always recommend using the fantastic Biomass Suppliers’ List (BSL) for a comprehensive list of high quality suppliers across the UK.

Can I use any kind of pellets?

The pellets will need to be ENPlus A1 or A2. These are 10-12mm long and 6mm in diameter. Your wood pellets need to be dry, clean, mechanically robust and possess an ash content defined by appropriate standards. They need to be able to flow freely and delivered via a pneumatic system. Check out this handbook from HETAS for more information about wood pellets.