Retrofitting an outdoor furnace to burn biomass

HeatMaster outdoor furnace ready to be retrofitted with a biomass burnerThe outdoor furnace is a widespread heating solution in Canada, especially in rural environment. It can heat hot water networks that can be easily used to heat houses, garages, farm buildings or even dryers. Many buildings can be connected to a single furnace and heating with wood is quite cheap.

However, these furnaces have some major drawbacks. Having to fill the outdoor furnace by hand, usually several times a day, means that the user can never go too far away. Filling the furnace becomes hard work especially during winter storms, moreover if a nasty bug drains your force. Moreover, even if most furnaces are driven by a thermostat, it is quite common to get your furnace cold by fuel depletion. As a result, room temperature in the heated buildings has a tendancy to change a lot during the day. Finally, when the furnace is hot and the fans do not feed the fire anymore, the furnace emits some thick smoke. That smoke contains a lot of fine particles and usually is not appreciated by the neighbours.

A solution exists: the biomass retrofit

Biomass flame inside the fire chamber of the outdoor furnace

Säätötuli biomass burners are easy to fit on most of the existing outdoor furnaces. Depending on the output of the furnace, they can usually be fitted with Säätötuli STRONG, Metri2 or Kaks2 feeding systems with a Säätötuli biomass burner and a C110 control box (120 or 240 VAC depending on the installation site).

Advantages of biomass retrofit on an oudoor furnace with a Säätötuli biomass burner:

  • No more filling the furnace daily or more, you can fit a hopper that will last several days and that is easy to load with the front loader of a tractor.
  • Pleasant and constant heat. The automation is connected to the furnace’s thermostat and keeps the desired temperature by idling or running the burner depending on the real-time need.
  • You can use as well wood-energy chips or pellets. Säätötuli burners are well known for their versatility regarding different solid fuels.
  • Increase your relationship with your neighbors. No more smells nor visible smoke, the Säätötuli biomass burner optimizes the combustion and avoids emissions of unburnt gases.

Example: biomass retrofit on a HeatMaster MF20000 outdoor furnace

Prior to the installation, a hole was made at the rear of the outdoor boiler, allowing the biomass burner to be installedThe customer heats two big houses and a garage with a HeatMaster MF20000 outdoor furnace (about 800 000 BTU/hr). Based on the number of cords the customer uses every year, he decided to retrofit his furnace with a 150kW (511 821 BTU/hr) Säätötuli biomass burner.

The Säätötuli 150kW (511 821 BTU/hr) biomass burner is inserted inside the outdoor furnaceThe outdoor furnace was modified by adding a hole at the rear to fit the burner inside the fire chamber. During the installation, the burner is fitted on position and remaining gaps are filled with fire-resistant rockwool.

The Kaks2 biomass feeding system is connected to the burner and a silo is built on top of itTo increase the time between hopper fillings, the customer chose to combine the burner with a Kaks2 feeding bottom. The Kaks2 bottom connects to the burner with an auger. The customer built himself hopper walls on top of the Kaks2 feeding bottom.

Once the control automation box is connected, the outdoor furnace is ready to be used with woodchips or pelletsThe Säätötuli C110 control automation box is a good solution for retrofit purposes on outdoor furnaces. The burner output is piloted by the furnace's own thermostatOnce the mechanical installation is done, the control box is installed and all the motors and control systems are wired. The thermostat of the furnace is connected to the automation box and will drive the burner to keep the furnace at the desired temperature.

With correct setup of the primary and secondary airs, there is no smells nor visible smoke at the chimneyOnce the startup and the training are done, all that remains to do is to benefit of a continuos heat with no smoke. The furnace burns now woodchips that are made in the farm with a PTO-driven chipper. During the coldest days, the hopper is filled twice a week with the tractor’s front loader.

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You can see a video of a retrofit burner at the Courcelle’s fair.