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Wood Gasification Boilers

A wood gasification boiler
A wood gasification boiler

Wood gasification boilers are a very simple boiler. They work by burning logs in a combustion chamber. They are loaded once and then burn the logs in one go, taking between 2.5 and 3.5 hours, and providing up to 120kW of heat. The created heat is placed in a large buffer tank and can be used as required throughout the day.

Loading and starting the boiler is very simple:

Once loaded and lit, the boiler needs no further attention.

The Thermal Store

Every gasification boiler needs to be installed with a thermal store of "buffer" store. This thermal store will vary depending on the model used but will contain between 1000 litres and 2000 litres of storage. This is beacuse the thermal store must be sized so that it can hold the energy produced during a firing cycle of the wood boiler.

The thermal store will normally be a large and well insulated water tank. 1000 litres of water can store 1.16 kWh per degree of temperature difference. Typically, a A 30kW boiler will need about 1500 litres of thermal store. A 37 kW boiler will need about 2000 litres.

Once the thermal store has been heated, heat can be automatically controlled and zoned and used as needed, the same as in any modern heating system.

Wood Gasification Boilers from Varmebaronen

Sweden is the world's largest market for wood pellet and wood gasification boilers. In fact, in 2006 Sweden used as many wood pellets as Germany, Austria and Italy combined.

We have chosen Varmebaronen, one of Sweden's largest wood pellet and wood gasification boiler manufacturers as our partner for biomass boilers.

Vedolux 37 Boiler
Vedolux 37 Boiler

The Varmebaronen range of wood gasification boilers are downfiring and burn the split logs by providing a negative draft from below. This causes around 80% of the dry weight of the wood to be converted into a gas, which burns very efficiently.

There are two models available. The Vedolux 30 is a 30kW boiler and must be installed with a minimum buffer size of 1500 litres.

The Vedolux 37 is a 37kW boiler and must be installed with a minimum buffer size of 2000 litres.

Where more than one burn per day is required (e.g. in the case of buildings requiring >120kW per day), a suitably sized larger buffer must be used.

Benefits and Features:

  • Simple yet strongly constructed
  • High quality Swedish product
  • Fan assisted flue keeps chimney height to a minimum
  • Easy to clean, everything accessed from the front.
  • Combustion chamber for 500mm firewood logs

More information on these two boilers and on the flue available can be found by visiting the Wood Gasification Boilers product group.


Stainless Steel Flue
Stainless Steel Flue

Above: Acceptable methods of fluing a wood gasification boiler

To provide proper operation, pellet boilers typically require a draught from the flue of -20 pascals. This generally means that the require a fairly high flue or chimney. The pellet boilers supplied by RVR have a built in fan which means the minimum flue height can be much lower. The minimum height is 3.5 metres from the bottom of the boiler. The cross sectional area of the flue should be Ø100- 160 mm. 150mm is recommended.

It is important to use an insulated flue so that the flue gases do not drop too low while rising up the flue. If this happens condensation can occur and the corrosive water released can drop back down into the boiler and cause damage.

RVR supply a range of insulated stainless steel flue.

Installing a wood gasification boiler

When a plumber installs a wood pellet boiler, it is important that the following items are given special attention:

  1. All requirements outlined in the boiler instructions must be fulfilled
  2. All settings and checks outlined in the burner instructions must be fulfilled
  3. All connections are watertight.
  4. Connections to the boiler and to the flue are sound
  5. The filling/drain valve has been closed properly
  6. The safety valves are working properly
  7. A suitably sized buffer has been installed,
  8. The installer should fire the system with a small load of wood and let it come up to temperature

Cleaning the boiler

Wood gasification boilers are designed to operate with minimal cleaning. The cleaning schedule will depend on the type of wood used but will typically be every two to three weeks in winter. The user can tell when cleaning is needed by observing the flue temperature. A rise of 50°C above the temperature of a clean boiler indicates that cleaning is required.

Cleaning involves opening the combustion chamber and cleaning out the ashes, and using a long flexible brush to clean the ash out of the boiler tubes. This is a very simple process which takes about 10 minutes, requires the minimum of bending and all items can be accessed from the front.