Hamilton Energy Consulting

Energy advice for a carbon constrained world

Case Study: An Advanced Wood Fired Boiler.

The Brief.

A major extension to a farm house was planned, and the about to retire owners wanted to live there as far into their old age as they could. The only utility service available at their farm was the electricity grid; however the owners were aware of the potential for ever increasing electricity prices to eat into their savings and wanted to put some capital into heating solutions that would provide both low running costs and the minimal use of fossil fuels. The farm’s major focus was plantation forestry, so plentiful supplies of sustainably produced firewood were available.

Convenience and minimal environmental impact (in the form of smoke emissions) were another concern; the owners in particular did not want to wake up to a cold house which could be heated only by starting a fire from scratch or by reviving a fire kept smouldering and smoking overnight. Another dimension of convenience was flexibility; occupancy of the extended farm house was expected to fluctuate significantly over time, and the owners wanted to heat or not heat sections of the house as required. The house site was located between 300 and 400 metres above sea level in northern Tasmania, and so heating was a major consideration.


The combination of desired minimal operating costs, minimal reliance on fossil fuels and on-farm availability of sustainably produced firewood all led immediately to a wood heating solution. None of the technologies commonly deployed in Tasmania were able to meet the criteria; the closest was the use of a wood fired cooking appliance with an integral central heating boiler and hot water radiators.

The suggested alternative was the importation of an advanced wood fired boiler from Germany, a technology not known to have been used in Australia before, but relatively common in Europe.

The Adopted Solution.

Wood Fired BoilerA “system package” was purchased from Paul Künzel GmbH and Co. of Hamburg, Germany. The package included a 47 kW log boiler, three hot water vessels, two control boxes and associated valves. The advantages of the Künzel system design were:

  • highly efficient two-stage microprocessor controlled combustion;
  • the use of insulated water tanks as heat stores allowing the boiler to run in batch mode;
  • compliance with European smoke emission requirements;
  • ability to use heat from the boiler to back up a solar hot water system;
  • a system control panel able to be centrally located, away from the boiler; and
  • electric ignition on the boiler, allowing it to be set up to run automatically when additional heat was required.

Installation and Commissioning.

As this was the first Künzel system in Australia, installation and commissioning required working closely with the plumber and electrician to ensure that the various sensors were correctly wired up and that the piping configuration would work as intended.