Why You Won’t Need a Wood Burning Stove in a Passivhaus - Even in a Power Cut
Wood-burning stoves are now banned in all new build homes across Scotland, due to changes in building regulations that came into force in April 2024.
What are the new rules on wood burning stoves?
New build homes in Scotland will no longer be allowed to install polluting heating systems such as oil and gas boilers, and bioenergy sources — like wood burning stoves.
Instead, climate-friendly alternatives like heat pumps, electric boilers or storage heaters will need to be installed. This is known as the New Build Heat Standard (NBHS).
The new rule includes some exceptions. Wood burners can still be installed in new builds if a ‘need can be justified’, such as for emergency heating. Additionally, homes with existing wood burners won’t be forced to rip them out. However, Scottish ministers are working on proposals for existing homes and buildings.
Why have the rules changed?
Heating our homes and buildings accounts for a fifth of Scotland's carbon emissions and the Scottish Government says the new standard will help meet its legally-binding target to reach net zero carbon emissions by 2045.
Wood burners are usually considered a more sustainable heating method because they don’t rely on fossil fuels such as oil or coal. However, using a wood burning stove or open fire at home contributes to a pollutant called fine particulate matter.
Scotland’s New Build Heat Standard comes a year ahead of UK government plans to ban fossil fuel heating systems in all new build homes (non-domestic buildings are excluded) in England from 2025. Wales is working to the same time frame, having already prohibited the use of gas boilers in newbuild social housing in 2021.
What is the controversy?
The new law has raised concerns among Scotland's rural and island communities, where frequent power cuts make wood burning stoves essential for heating.
Storm Arwen in November 2021, for example, left more than 100,000 homes and businesses without electricity for several days, with some in the North-East enduring outages for more than a week.
As climate change is expected to bring more intense storms, Scotland's homes may face even greater risks of prolonged power outages in the future. It’s vital, then, that our new homes are resilient against such events—and fortunately, there’s already a building standard which ensures that.
Why Passivhaus is the solution
Developed in Germany in the 1990s, Passivhaus is accepted as the world’s leading low-energy building standard.
Homes built to the standard are proven to remain habitable for longer during power cuts or loss of heating fuel. Occupants are kept comfortable for up to a week, even in extreme cold weather.
The heating failure study
In 2023, the International Passive House Association published a technical study that used simulation to compare the habitability of homes during a heating system failure. In the scenario, heating was cut for seven days at the end of a wintry January, as outside temperatures dropped to -13°C. Electric appliances and the ventilation system continued to operate.
The study compared the performance of three different types of properties:
— An old home
— A Passivhaus
— A home built to Germany’s low-energy building code, the Energy Conservation Ordinance (EnEV)
What do the results reveal?
The living rooms in each of the three homes started with a temperature of 22°C. When the heating was cut, the old home (represented by the blue line) becomes unpleasantly cold and uninhabitable within hours, despite having double glazing. After a few days, there's a risk of water pipes freezing as internal temperatures plummet to 0°C.
The home built to Germany’s low-energy building standard, EnEV (the orange line), takes just one to two days to drop below a cold, uninhabitable 15°C.
In stark contrast, the temperature inside the Passivhaus (green line) remains almost within a comfortable range. Only after more than a week does it get colder than 18°C.
The power cut study
A 2021 study from Norway produced similar results. In this scenario, a home in Oslo experiences a power cut for four days, starting on the 14th January – statistically the coldest day of the year.
Two types properties are compared, both with and without battery storage and PV solar panels:
– A home built to Norway’s building standard, TEK17. One of the strictest low-energy building standards in the world.
– A Passivhaus
What do the results reveal?
The living rooms in each home started with a temperature of 21°C. When the power is cut, the TEK17 home (without PV solar panels or battery storage) falls below 18°C within a few hours. This is cold, but liveable. However, the next day, the temperature drops below an uninhabitable 15°C. When power is restored, it takes 12 hours of heating before the indoor temperature returns to normal.
In contrast, the Passivhaus (without PV solar panels or battery storage) maintains a comfortable temperature for more than 24 hours. It takes four days for the temperature to fall below 15 °C. The Passivhaus remains habitable for twice as long as a TEK17-compliant house and is considerably faster to return to a normal temperature.
Extra technologies like solar panels and storage batteries further improve both home's resilience during a power cut (see the blue and red dotted lines in the graph). Although they have much better impact in the Passivhaus.
Why does a Passivhaus stay comfortable even if power and heating is cut?
How fast a home's temperature drops depends on its thermal insulation. The more insulated a home is, the slower it cools down.
Passivhaus homes are packed with far more insulation than a standard home and are virtually airtight, with even the smallest gaps plugged with adhesives and tapes to stop heat escaping.
High-performance doors and triple-glazed windows also contribute to their exceptional energy-efficiency. These components work together to seal the Passivhaus like a vacuum flask, protecting it from the elements.
The primary goal of a Passivhaus is to maintain a comfortable indoor temperature with minimal reliance on heating systems. Most of the home’s heat is supplied by ‘passive’ sources, mainly sunlight, along with the body heat of occupants and running appliances, ie - boiling the kettle, watching tv, showering and cooking.
Scottish Passivhaus equivalent on the horizon
The New Build Heat Standard and its impact on wood burning stoves point to the Scottish government gearing up for all new homes in Scotland to be built to a Passivhaus equivalent standard.
It follows a 2021 recommendation from the Scottish government’s Climate Assembly that ‘within the next five years, all new housing is built to Passivhaus standards (or an agreed Scottish equivalent)’.
The new rules will cover custom and self-build homes, as well as social housing. Scottish equivalent to the Passivhaus standard goes out to consultation in summer 2024 and is due to be adopted as legislation in December 2024.
Coldwells Build Passivhaus Collection
In winter 2024, we’ll launch the Coldwells Build Passivhaus collection. Modern, prefabricated homes built to world-class standards – the first of their kind in Scotland.
Developed in partnership with Scotland’s leading Passivhaus designers, John Gilbert Architects, the Coldwells Build Passivhaus comes in six contemporary, light-filled designs ranging in size from 2 to 5 bedrooms. The homes will be manufactured in our Aberdeenshire workshop by our in-house Passivhaus-certified craftspeople.
For release dates of the Coldwells Build Passivhaus collection, register below.
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To view the Coldwells Build Passivhaus designs before their official launch in winter 2024, register today.
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