Clean Air Strategy

David Fletcher looks at the options for boat stoves in the light of new regulations.

DEFRA has just updated its report on the Clean Air Strategy. This is all about the impact of pollution from solid-fuel stoves. DEFRA is telling us how it intends to tackle these (and other) sources of air pollution, making our air healthier to breathe, protecting nature and boosting the economy. Air quality is known to be the biggest environmental health risk in the UK, as it shortens lives and contributes to chronic illness.  Health can be affected both by short-term, high-pollution events and by long-term exposure to lower levels.

The concerns about solid-fuel stoves are the emission of fine particulate matter in the smoke, and sulphur dioxide, the pungent smell from burning fuel. Burning wood and coal in open fires and stoves makes up 38% of the UK’s emissions of fine particulate matter. To tackle this requires two things: using appropriate fuels, and designing and using the stove so that combustion is complete. The best practice for fuel is well known and nothing new: if burning wood, it must be dried out (or seasoned) before going into the stove. The water content can be checked with a simple and cheap damp-meter. Almost all problems associated with burning wood are caused by damp fuel. Taking wet logs from a roof basket to put straight onto a fire sucks the heat out of the fire and causes incomplete combustion. The smoke emissions increase (with dense white smoke), carbon monoxide goes up, and the boat next door is none too impressed. A log of fresh wood will contain about a mug of water and the steam produced when this ‘burns’ doesn’t help the stove either. For black fuels, the use of smoke-free is best practice; house coal is full of tars and toxins and should not be used.

DEFRA is not suggesting changes to the best practice. It says that it will legislate to prohibit the sale of the most polluting fuels, make changes to existing smoke control legislation to make it easier to enforce, and give new powers to local authorities to take action in areas of high pollution. In general there is nothing to fear with this so long as we do what we know to be sensible when choosing fuel. If you are dependent on wood from the canalside, then you must make the effort to store it under cover and dry it out before use. The sting in the tail is the last part concerning local authorities. It implies that, say, in London, Boroughs may decide to ban solid-fuel stoves because of extreme pollution levels in their locality.

But is there something more that can be done? The other thing that can help is the choice of flue and stove. For the flue, the aim is to increase the efficiency of burning by keeping the flue hot, because this gives the fire good draught, even when turned down, and it also aids more complete combustion. A bare flue, cast-iron roof collar or uninsulated top chimney, all have the effect of chilling the rising flue gas, and this reduces the draught in the flue, causing incomplete combustion. Insulated wall flues have been around for a while and as time goes by improved designs are coming out and prices are coming down. They are certainly proven, if costly. For stoves there is new technology: the focus is now on stoves that are referred to as ‘clean burn’, which are equipped with primary, secondary and tertiary air supplies. These provide better fuel efficiency and also significantly reduce emissions. Taking the standard Squirrel stove as an example, the primary air wheel is at the bottom and controls the air though the grate. The secondary air supply enters via the wheel above the glass and is often called the ‘air wash’ system, which ensures that the glass remains clear. The new facility is tertiary air, which enters the body of the stove at the top, through an air-box, usually at the back. The preheated tertiary air improves the secondary gas burn-off by burning, re-burning and re-igniting gases and particles created during the first burn in the grate. This has the double benefit of improving the efficiency of burning by using less fuel for the same heat output, and also reducing the particulate content of the smoke.

We can expect greater emphasis to be placed on emissions, and these clean-burn systems are a solution that is coming down the line fast. On this issue, DEFRA says it will legislate to ensure that only the cleanest stoves are available for sale by 2022. It is currently giving approval for clean-burn stoves when they are intended for use in smoke control areas. So, can we expect older designs to be banned and taken off the market, or will they be allowed to be used outside cities? There has been a steady tightening of regulations for stoves for what many believe to be purely political reasons. But momentum is gathering and we can expect regulations will tighten yet further over time. As a consequence, getting a stove with DEFRA approval is key, especially for use in smoke control areas. A clean-burn stove and insulated flue is the only way to do this. And we cannot expect to have grandfather rights for old stoves in places like central London. They will be banned. So if you are in the market for a new stove, take care to look at one that has DEFRA approval. It could be an expensive mistake to buy old technology just now.