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Why You Won’t Need a Wood Burning Stove in a Passivhaus - Even in a Power Cut

Over the past week, a row has broken out over the use of wood burning stoves in Scotland.

New building regulations which came into force at the beginning of April ban the heating appliances from new build homes. The new rules have no impact on homes that already have wood burners.

A black woodburning stove. Logs sit on a basket next to the stove. A chair sits next to the basket with a throw draped over it.

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 and heat networks will need to be installed. This is known as the New Build Heat Standard (NBHS).

There are some exceptions. Wood burners can still be installed in new homes to provide emergency heating, where a need can be justified.

Homes that already have a wood burning stove won’t be forced to rip it out. However, the government is developing proposals for existing 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 regulations will contribute to its target to reduce greenhouse gas emissions to net zero by 2045.

Wood burners are often viewed as 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 is a major contributor of a pollutant called fine particulate matter.

What is the controversy?

The new building regulations have troubled some of Scotland’s rural and island communities who are prone to power cuts and rely on wood burning stoves to keep warm.

One of the latest major events was Storm Arwen in November 2021, which left more than 100,000 homes and businesses throughout Scotland without electricity for days. Some in North-East Scotland had to cope without power for over a week.

In the years and decades ahead, Scotland’s homes are likely to become more vulnerable to extended power outages. Climate change is projected to cause a wide range of impacts, including more intense storms.

Therefore, it's crucial our new homes are resilient and can withstand disruptive weather events. Fortunately, there's already a building standard that can do exactly 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 a freezing -13°C. Electric appliances and the ventilation system continued to operate.

The study compared the performance of three types of properties:

— An old home
— A home built to Germany’s low-energy building standard, the Energy Conservation Ordinance (EnEV)
— A Passivhaus

X-Axis: Date, Y-Axis: Temperature ºC • Source: International Passive House Association

What do the results reveal?

The living rooms in each home started with a temperature of 22°C. When the heating was cut, the old home – despite having double glazing – gets unpleasantly cold within hours. After a few days, there's a risk of water pipes freezing as internal temperatures plummet to 0°C. 

The newer home, constructed to meet Germany’s low-energy building standard (EnEV), takes just one to two days to drop below a cold, uninhabitable 15°C.

In stark contrast, the temperature inside the Passivhaus 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 home built to the Norwegian Passivhaus Standard, NS3700.

Home built to Norway’s building standard, TEK17 • Source: Shabnam Homaei & Mohamed Hamdy
Home built to the Norwegian Passivhaus Standard, NS3700 • Source: Shabnam Homaei & Mohamed Hamdy

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 rules 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.

The new legislation will cover self-build homes, as well as social housing. A cross-industry working group is currently developing Scotland's Passivhaus equivalent standard, with a thorough consultation on the proposals happening in 2024, and then formally implemented by 2025.

Coldwells Build Passivhaus Range

In 2024, we’ll launch the Coldwells Build Passivhaus range. 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 range, register below.

Read Time: 2 minutes Type: Passivhaus, Advice - Author: Clare Booth, Director Share:

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