As the trend towards sustainability continues not only in architecture and construction but the world at large, the industry is constantly coming up with new ways to consume less, conserve more, and generally put what we have to better use. Johnson Controls’ 2018 Energy Efficiency Indicator Survey identified energy efficiency as a huge driver in the construction and operation of commercial facilities globally - and the same goes for urban developments such as Sydney’s The Fern.  

For years, all new residential construction has had to comply with the energy efficiency provisions in the National Construction Code, and across Australia the 6-Star Standard has been adopted as the baseline for thermal performance. 

But as demand for sustainable housing grows, people are increasingly opting for designs that deliver higher 7-10 Star energy ratings and yield economic and environmental benefits. With so many structures with high thermal performance under construction, designers and specifiers are increasingly turning towards smaller footprint heating solutions that fill the need for a modern aesthetic while delivering ample levels of radiant heat. 

Sleek, European-styled and design-focused wood-fired heaters like the contemporary Morso and Austroflamm ranges offered by Castworks are gaining popularity in energy-efficient buildings as they better meet the changing heating needs of high-thermal-performance construction. These models are some of the few that meet the stringent standards of the DIBt (German Institute for Buildings) - more on that later. 

What is Passive House?

Passive House (from the German Passivhaus) is a concept that has been around for the better part of 30 years, originating in Europe. The core premise of Passive House is that adopting a few key design principles can enable the creation buildings with healthy, dry indoor spaces that require little or no heating or cooling.

There are 5 basic principles to adhere to: 

  1. Insulation
    Choosing appropriate materials and installing sufficient amounts of insulation within the building’s envelope to provide enough thermal insulation between the outside and inside climates.
  2. Insulated windows
    The requirement for appropriate insulation carries over to the building’s windows as well. In Australia this typically means double-glazing, though triple-glazing may be required in some more extreme climates.
  3. Airtightness
    Creating an airtight design with minimal planned gaps or cracks in the insulation barrier, serving to keep heat in (or out, depending on the season).
  4. Mechanical Heat Recovery Ventilation
    This provides a flow of clean, filtered air to the building. Put simply, a Heat Recovery Ventilation system draws stale air out, replaces it with fresh air and transfers heat from the outgoing air to the fresh air in the process. 
  5. Removing thermal bridges
    A thermal bridge is a material or pathway that allows heat to travel from the inside to the outside of the building. In order to maintain the integrity of the building’s insulation, the fewer thermal bridges in the construction, the better. 

Heating benefits of Passive House

For a new build Passive House, the total heating demand must remain under 15kWh/m²/year (and meet other criteria) in order to gain full certification from the International Passive House Institute. There’s a clear topline here: higher thermal mass mean a smaller heating outputs are required to maintain comfortable temperatures. This means that rather than a ducted or other centralised heating system being a requirement, specifiers can opt for smaller solutions such as modern wood fired stoves, which offer both aesthetic value and practicality. 

Smaller heat footprints

Passive Houses have a vastly reduced heating demand than regular houses - generally only needing about 10% of the energy that would otherwise be required. This means that rather than whole-of-house heating, room-specific heating is preferable, and a small-footprint heating solution is ideal. An Austroflamm Woody for example, delivers a nominal heat output of 7kw, ample energy to heat spaces of 100-120m². A Certified Passive House may only need 1-3kW of space heating input. The difference can be moderated through fuel - if you only put in 3kW worth of fuel you will only get 3kW of heat out. This means that specifiers can keep the visual impact and design aesthetic of a modern European wood fired stove whilst maintaining suitable heating levels in high thermal mass dwellings.

Radiant heat vs convection

In addition to studies showing that radiant heating is 30% more efficient than convection heating, there are numerous benefits to radiant heat. Radiant heating delivers better heat distribution as air is not being continuously shifted around the building, resulting in more uniform heating and less temperature difference between areas. Choice of material is important when selecting a source of radiant heat. Opting away from materials like steel and towards cast iron allows a more gradual release of heat throughout the space. Cast iron has a much greater heat-life than steel and coupled with soapstone heatbank options, Morso woodstoves able to retain significantly more heat while keeping the stove within the comfort zone, thus extending the efficiency of each fuel load. 

Direct air kits for increased efficiency

Some wood fired heating solutions come with options for direct air intakes. These alleviate the possibilities of any issues that may arise from negative house pressure (namely internal smoke from the wood fire) and maintain the strict thermal mass requirements for Passive House by providing oxygen for the fire while remaining tightly sealed to prevent heat loss for the rest of the house. 

Australian standards for wood-fired heaters

Since 1992, wood heaters in Australia have been required to comply with standards for emissions and efficiency; in 2019, these requirements are changing.  AS/NZS 4013:2014 Domestic solid fuel burning appliances—Method for determination of flue gas emission stipulates that heaters installed before August 2019 must meet an emission limit of 2.5g of emissions per Kg of wood burnt (compared with up to 12g from non-certified heaters or 17g from an open fire) and a minimum efficiency rating of 55%. However, products installed after the September deadline will have to achieve emissions of no more than 1.5g/Kg and efficiency of 60%. All will still need to be marked in accordance with AS/NZS 4013:2014as proof of efficiency. All compliant wood heaters sold in Australia will have a certificate of compliance – ensure as a specifier you insist on only compliant heaters meeting current standards.

Meeting DIBt requirements

The vast majority of wood stoves are not compatible to work in tightly-sealed homes in combination with Mechanical Heat Ventilation Recovery units. In order to be certain that they are not using any of the air from within the dwelling or releasing carbon monoxide into the air supply, they must have direct air intakes and have a stove door seal that’s passed the DIBt (German Institute for Buildings) test. The process involves pressure-testing the airtightness of door seals in excess of 6,000 opens and closes and in addition to guaranteeing safety for use in passive house, stands as an international mark of prestige and good design. Heaters from Morso and Austroflamm are some of the few that have passed the DIBt test, but specifiers are advised to seek the advice of licensed distributors like Castworks for further detail. 


Castworks offers a range of stylish, functional and effective wood fired heating solutions to suit modern energy-efficient constructions. For 20 years Castworks has been one of the most respected importers and distributors of home heating products to the Australian market, partnering with global manufacturers from countries as diverse as Denmark, the UK, Spain, Portugal and New Zealand. Castworks sources sophisticated heating products that are efficient, compliant and meet the needs of the Australian market. 

Castworks has a stylish heating solution for every home, including the ADF range of contemporary insert and freestanding fireplaces, the award-winning cast iron Morsø stove range, and the Hergom Glance L - new to Australian from Copenhagen design studio Strand+Hvass.They also have an extensive spare parts portfolio, such as replacement baffles and ropes – everything you need to install a stylish wood-fired heater in your Passive House.