Green Services Direct

Log burners are aesthetically pleasing but how green are they?

Cosy and characterful, wood burning stoves make a fabulous focal point in homes across the UK.  In fact, an estimated eight per cent of the population in this country have one, according to a report from Kantar. The most common reasons homeowners gave for having a wood burner was to create a homely feel, to heat one room or because they like the look of a real fire. With rocketing fossil fuel prices, more people could install wood burners to heat their homes rather than for aesthetic reasons. But in an age of global warming, is it green to use wood as a heating fuel?

The green credentials of burning wood

For more than a decade the EU has been subsidising wood burning. Wood is now Europe’s largest renewable energy source, far ahead of solar and wind. Drax, the UK’s biggest  biomass plant, is burning the equivalent of 25 million trees a year to supply electricity, according to an investigation by the Daily Telegraph. A company spokesman told the newspaper that they play “a critical role in generating 12 per cent of the UK’s renewable electricity” to keep the lights on and work towards next zero goals.

International climate accounting rules mean that wood power counts towards clean-energy targets. Wood qualifies as renewable energy on the basis that we can always grow more trees.  As demand surges amid a Russian energy crunch, companies in central Europe and the USA  are logging swathes of forests to supply pellet mills and biomass power plants.

Despite the green subsidies, new scientific research suggests burning wood can be dirtier – or generate more emissions per unit of power - than coal. The problem is one of timing. All the C02 absorbed by the tree in the years, or even decades, it was growing  is released in a few minutes it takes to burn.  Unlike coal, trees can be replaced by saplings and when grown will reabsorb all the carbon dioxide in the atmosphere, say supporters of wood energy.

But researchers, led by John Sterman at Massachusetts Institute of Technology (MIT), found it can take a very long time to pay off that carbon debt – 100-plus years for a forest to grow back. That’s if – and it’s a big if - those saplings mature, say researchers. Wildfires, disease or development could all wipe out those young trees. Using wood harvested for burning will increase carbon in the atmosphere and make global warming worse in the 21st century,  they warned.

Later this month (September, 2022), the European Parliament is to vote on a bill that would shake-up subsidies and prohibit the logging of whole trees for energy use. Only energy from wood waste like sawdust would qualify as renewable and be eligible for green subsidies.  Bioenergy Europe, a trade association, opposes cutting subsidies or changing how clean energy is defined. It argues problems are rare. When harvested correctly and sustainably, wood remains important as a renewable energy source, it argues.

How eco-friendly are wood burners?

How energy efficient and clean your stove is will depend on its age and design. A new Ecodesign Regulation came into force in January 2021, setting higher standards for appliance efficiency and emissions – tiny harmful particles - for new models than previous generations of stoves. Only models that meet the ecodesign standard can now be sold in the UK. Some manufacturers had already adopted the new  standard with a so-called “Ecodesign Ready” stove.   The standards cover minimum efficiency plus maximum levels of particulate matter, carbon monoxide, nitrogen oxides and organic gaseous compounds.

Independent tests show that a stove meeting the requirements of Ecodesign, such as the Clear Skies certified model, produces up to 90% less particulate emissions than an open fire, according to the Stove Industry Alliance, a trade body. An Ecodesign stove will also use much less fuel than an open fire.

Downsides of wood burning stoves

Wood burners can give out too much heat. A room with a 5m x 5m floor area in a house built to current building regulations standards of thermal efficiency will need a maximum of 1.4kW through the winter. And all of that will be provided by the principal heating system. Most woodburning stoves with well-dried hard logs will give out 4kW, enough to make the room feel uncomfortably hot. In older, less well insulated homes or bigger rooms, this extra heat may be needed.

There are other downsides. A study by European Environmental Bureau, called  ‘Where there’s fire there’s smoke,’  found even Ecodesign stoves, billed as more environmentally friendly, can emit 750 times more harmful tiny particle pollution, called PM2.5, than a modern HGV truck. The Ecodesign standard allows wood stoves to emit 375g of PM2.5 for every gigajoule (GJ) of energy produced. By comparison, the latest standard for HGVs is 0.5g per GJ.

The report says the huge disparity in pollution levels is because combustion in HGV vehicles is highly controlled, for example with filters and catalytic converters required by law, whereas burning wood in stoves involves uncontrolled factors, such as air flow and fuel quality. Researchers said the use of wood burning stoves should end to tackle deadly air pollution and boost health with heat pumps installed instead.

In 2017, a UK Government air quality expert group assessed the grams emitted an hour from ecodesign stoves and found it to be six times higher than HGVs.

Air pollution

In the UK, domestic wood burning is the single biggest source of small particle air pollution, producing three times more pollution than road traffic, government data shows. Just eight per cent of the population cause this air pollution, according to Kantar’s report. Government statistics show that domestic wood burning in both closed stoves and open fires was responsible for 38% of the pollution particles PM2.5 in 2019, the latest figures available. And emissions from this source had more than doubled since 2004 due to the huge popularity of wood burning stoves. By comparison, road traffic caused 12% of PM2.5 in 2019.

Tiny particle pollution (PM 2.5) is harmful to health as it can pass through the lungs into the bloodstream and be transported around the body, lodging in the heart, brain and other organs.

Wood burners also triple the amount of harmful pollution inside homes and should be sold with a health warning, scientists have warned. Experts at Asthma UK and the British Lung Foundation have urged people to use wood burners only if they had no alternative heating.

The UK Government has no plans to ban wood burning stoves. But new legislation means all wood sold for domestic use must have a moisture content of less than 20%. Wet wood must be sold with advice on how to dry it before burning.  The regulations also cover manufactured wood products, such as briquettes, heat logs and fuel logs with a focus on limiting sulphur content of their emissions.

Greener solutions?

One eco-friendly alternative to a wood burning stove, is a bioethanol fireplace. They provide the look of real flames without the smoke or  hazardous fumes and burn at 98% efficiency, according to stove and fireplace specialist Chesneys.  While they may not generate as much heat as a stove or offer the crackle or smell of burning wood, they provide a solution to many of the drawbacks of wood burners.

Bioethanol fuel is a form of renewable energy produced from common crops, such as sugarcane, corn and hemp. When burnt in air the only emissions are water vapour and a small amount of CO2 There are no particulates and no carbon monoxide, so they cause less air pollution. What’ s more, they are simple to fit and no chimney is required.

Bioethanol  fireplaces come in a variety of styles. They can be slotted into a traditional fireplace or there are contemporary wall-mounted and freestanding versions available. Bioethanol’s green credentials aren’t perfect, but they tick quite a few boxes, say experts.

People have heated their homes with wood for millennia. That sense of hearth and home and comfort of gathering around a roaring fire on a cold winter night is hard-wired into our brains. But burning wood to produce heat and electricity is far from green and can even increase the carbon emissions causing the global climate crisis. Better insulation for our homes and alternatives, such as heat pumps and bioethanol fireplaces, are better for our planet and health.