19 Feb 2010

Whither the Wood Burning Stove?

On Wednesday this week I travelled down to Exeter to meet Stovax, making good a promise I made to them six weeks ago. I really new sweet FA about Stovax, other than they made wood burning stoves, and I quite expected a couple of beardies wielding hammers and tongs. How wrong I was. It's now a substantial concern. The business started in 1981 when Guy Brook and his friend Miles Jennings began firstly importing and distributing stoves and then making Victorian fireplaces and surrounds. It's been been expanding ever since, some of it by starting up new companies to produce fireplace products, some by acquisition of related businesses. Stovax Holdings now employs 450 people and has become the largest stove maker in the UK. The business includes several brands: Stovax, Yeoman, Gazco (makes gas fires - does well), Redfyre (ranges) and there is another, now separate, holding company which contains a tiles business called Original Style. "In fact everything to do with fires except hearths," explained Greg Taylor, the technical director.

Greg, it turned out, is in the middle of a selfbuild and he had spent much of the past few months buried in the Housebuilder's Bible. He brought along his copy and it was marked up with post-it notes. My first thought was that I was being ambushed, and that I would be forced to work in the foundry for the next six months until I saw the error of my ways. But of course he was sweetness and light, and actually very helpful as well. I learned a lot from him during our lengthy interview.

Like what exactly?

• The difference between a wood-only burning stove and a multifuel stove. Wood burns best when laid on a bed of ash with air being injected at it from above. In contrast, coal burns best in a grate with air coming from underneath. Wood will still burn in such a grate but not as well. So a multifuel is basically a coal grate, whilst the wood grates are rather different and would be hopeless for coal. Stovax have seen sales of wood-only stoves rise steadily over the years and now they sell pretty much 50/50 (wood v multifuel).

• Solid fuel stoves can get to around 80% efficiency, but anything beyond this is technically difficult because heat is needed to keep the flue operating well.

• Virtually no one burns straight coal anymore but there are any number of clean or smokeless coals. Anthracite is a naturally occurring coal that burns very clean, but it isn't widely used these days. Instead we usually use manufactured smokeless coal pellets, known as Ancit.

• The Clean Air Act is the legislation behind a number of Smoke Control Areas where it is not permitted to burn wood or coal. You can burn smokeless fuels such as ancit, but if you want to burn wood, you need to get a stove that meets the technically demanding PD 6434 standard, which DEFRA test for in Cheltenham. These "cleanburn" stoves are then passed for use in Smoke Control Areas. It's not an easy test to pass, the cost is around £8,700, and Stovax are currently putting a lot of their stoves through this test. The more efficient a stove is the less smoke there is. "Smoke is unburned fuel" I have noted down: QED the more efficient the stove is, the more of the wood it burns and the cleaner the resulting smoke is.

• One of the keys to getting the best out of a cleanburn stove is to burn dry wood, Greg recommended getting a moisture meter and making sure that you don't burn logs with a moisture content no greater than 20%, preferably 15%. He said in order to get a true reading, split the log open and apply the meter to the middle.

• We are not about to run out of wood as a fuel. There are currently around 285,000 domestic wood stoves installed into the UK, burning around one million tonnes of timber in total each year (that's nearly 4 tonnes each stove, which seems a lot). The Forestry Commission reckons we are have the potential to burn ten times as much timber before we run into capacity constraints. They have in place a "Woodfuel Strategy for England" which should release and additional 2 million tonnes each year by 2020. Which means we are going to have to buy an awful lot of woodstoves in the next ten years if we are going to consume all this extra timber. OK, I know a lot will end up being burned commercially, but still the domestic sector will have a significant role to play.

• Stovax spent three years trying to sell pellet boilers, but the interest was minimal. They have now abandoned the technology (for the time being) and are concentrating on wood-fueled boilers, like....

• The Stockton HB. These are designed to heat hot water for the cylinder and for a number of radiators, but they are still very much focal-point room fires, unlike the utilitarian pellet boilers which ideally need to be sited in a basement. I got shown the labs where they were testing a Stockton 14. At full pelt, it burns 6kg of dry wood an hour but this belts out 14kW to heat hot water for rads and 8kW out of the fire itself and into the room.

• Greg Taylor (pictured here with the Stovax Studio 2 in the test lab) was keen to emphasise "link up." Link up? It involves adding a woodburning boiler stove to an existing central heating boiler system. The system, through gravity and series of valves, is set up so that the gas or oil boiler switches off when the stove is lit and vice versa. “Link up” allows homeowners to maintain the convenience of a conventionally fuelled boiler whilst also dramatically reducing fossil fuel bills through the use of solid fuel as an extra source of heat and hot water.

“When you get up in the morning or come home from work in the evening, the conventionally fuelled boiler can have warmed your home and given you plenty of hot water. As soon as you have the stove lit, the boiler can switch off until it’s needed again. Add solar panels and your conventional gas or oil boiler will be used even less.”

• There was a sub-text going on here which we didn't really have time to explore, but which struck me afterwards. There is a subtle difference here between a boiler and a stove. You don't really want a boiler in your living room, something I know from personal observation, having stayed in a house with what claimed to be a "pellet-stove" in pride of place next to the TV. It was noisy, ugly and just plain mechanical. So anything which ranks as a "biomass boiler" is only ever going to be of interest to a rich minority who have utility rooms and/or basements, whereas a wood-burning boiler-stove appeals to a much larger grouping. What Stovax are aiming at doing is building kit which looks like a stove and yet acts like a boiler.

• Which brings us back to the Renewable Heat Incentive which is proposing to exclude wood burning stoves but to include pellet boilers at a deemed tariff of 9p per kWh for 15 years. The worked example (on page 50) suggests that this subsidy would be worth over £1,000 a year, £15,000 in total. The logic behind excluding wood stoves is explained on page 31: These present difficulties as it is extremely difficult to monitor how much they are used (they are usually a secondary source of heat, the use of which will be optional), and to what extent they are used with renewable fuel rather than, for instance, coal. Now this second objection could be addressed by making the Stockton and its ilk wood-only rather than multifuel, but the first objection is much harder to address, especially if Greg's linking theory is put into place. Whereas the consumer seems to be saying "we want stoves, not boilers" the subsidies are going to go to the boilers. But, as we have already established, pellet boilers are really only ever going to be of interest to people with relatively large houses.

• In fact exactly the same thing can be said about ground source heat pumps which generally require large gardens. The RHI would seem to be a very generous subsidy for already wealthy people. Next week, I am booked into the government's Renewable Heat Incentive workshop, and I expect some heated exchanges on this very topic. But I digress. the subject of this ramble is wood burning stoves, and this leads us onto...

• We discussed airtight houses and how wood-burning stoves might cope. In theory, it is possible to create room-sealed wood-burning appliances (just as balanced-flue gas-fires and gas-boilers are). In practice, it hasn't happened yet, although Stovax sells optional kits for many of their stoves to take external combustion air directly to the appliance. Current UK regulations (Part J) require that there must be an additional supply of air from inside the house for any stove over 5kW but as houses become tighter this regulation will need to change for new houses. Wood burning stoves do not yet have an agreed technology to make them fully room-sealed. There are some room-sealed prototypes being made in Germany but nothing yet in commercial production. So the future of wood-burning appliances in near-Passive House standard homes is as yet uncertain, but at the moment, if you aspire to build a Passive House, you can't have a stove in your living room.

• We touched on the issue of ventilation and just how complicated it is becoming. Apparently, wood stoves tend to work fine when the house is under positive pressure, but react badly to negative pressure. This makes sense, doesn't it? So designers of ventilation systems need to be aware if a wood-stove is planned.

I hope this is a helpful guide to where things stand re: woodburning stoves. It's not a topic I have any great expertise in, and I welcome feedback from anyone with something useful to add.


  1. Stovax are good, but we bought a Morso (wood only and smokeless approved) and are delighted with it. It is efficient, flexible and makes a real difference to the amount of gas we use.

    Just to make things more confusing, you could day that a wood stove is, amongst other things a venitlating device.

    Discussion of wood supplies usually seems to go straight into how many millions of tonnes we produce commercially and this is understandable but everyone I know with a woodstove gets the bulk of their supply very locally from waste. Old pallets, prunings from trees or shrubs, fencng etc. - there always seems to be someone who wants to get rid of wood, if it is too big to go in the shredder it'll go in the stove. Other than making automation easier, I really cant see the pont in using more energy to turn wood into pellets

    More evidence of the RHI being more about monitoring, control and bling than actually helping people to use more renewables

  2. Interesting the comment about room-sealed stoves (or lack thereof). Over here in R2000 land, it's the norm, not the exception. We have this model: http://www.icc-rsf.com/en/rsf/the-opel-2-fireplace

    The technical specs http://www.icc-rsf.com/en/rsf/technical-specifications-of-the-rsf-opel2-fireplace state that it is room sealed but can operate on room air (by opening the doors).


  3. "We are not about to run out of wood as a fuel"

    Bad news guys - we are already running out! Timber merchants near here are putting up prices on a monthly basis as good timber plantation is chipped for fuel.

    My local firewood supplier pulled out of the business a year ago as he couldn't bid high enough for standing timber.

    Total annual UK timber production is 9 million tonnes, plus 4 million potential from undermanaged woods - of which it is hoped 2 million tonnes can be brought to market by 2020.

    Yet power plants underway in Port Talbot and Anglesea would burn 5 million tonnes, and another planned near Middlesborough 3 million tonnes. Total planned capacity for biomass generation by 2020 is around 4GWe, burning the equivalent of 17 million tonnes of dry timber.

    That extra 2 million tonnes doesn't look so much anymore.

  4. "The RHI would seem to be a very generous subsidy for already wealthy people."

    Spot on! PVs too. In fact, it is shamelessly plugged in the money pages as an investment with fantastic returns, so long as you can get your hands on the necessary £1000s.

  5. I'm also finding our usual sources of wood drying up and prices increasing. I'm sure rural individuals will always be able to scrape around for something to burn but the idea of providing a significant amount of UK heat from wood seems totally flawed.

    Given the supply issue flagged up by Alan we probably don't need to mention that wood emits similar CO2 to coal when burnt. Sadly good timber that would have ended up in construction is being burnt.

  6. Interesting points. I hadn't thought about the industrial burning of timber. There was story this week about Drax power station starting biomass co-firing as well. This could very quickly use up all our spare timber.

  7. I haven't done the sums (Alan will) but I'd guess Drax would burn whatever you threw at it. Minimal capital investment and instant renewables credits.

    Likely to happen I would think.

    Still, better to burn it in a coal power station than in a boiler to heat a school. Not that I'd support either, just one is half as bad as the other and it's not the way round most people imagine.

    Your Eco Bollocks awards have been quiet for a while . . .

  8. A bit of history - the UK had a wood crisis in the late 16th C. due to burning too much of it. Forest cover went down to a very low 10%, which hasn't recovered to this day. Most of Europe has 30-40% tree cover and the north-eastern USA is 70% forest (parts of the USA have rural smog due to so many woodstoves).

    Anyway, after that, the UK went desperately looking for alternatives. The result was ... coal.

    In short, there are many better uses for wood and burning it probably makes climate change worse.

    As for someone's comment above re. geothermal, no a heat pump isn't geothermal. It's slightly improved electric heating, and you may be heated at the winter peak in demand by Didcot power station or possibly Ironbridge ... it depends where you're located.

    Geothermal energy is what helps to heat Southampton (and Iceland).

  9. Fashions come and go, that much is a given in life. What is currently becoming very popular are rustic, more earthly fittings and furnishings for the home. This is the obvious veering away from the very functional, minimalistic styles of brushed aluminum and glass that has been very popular for the past few years.Apart from faux beams and solid wood furniture, wood burning stoves have become more and more popular. These are stoves that, instead of having piped gas or electric heat to cook on and warm the room, burn logs and firewood on a bed of ash instead.woodburning stoves.

  10. Mark, like others commented, I was under the impression that many wood-burning stoves today are room-sealed. But I'm no expert, not user of such a stove - yet. A quick google seems to show that there are many stoves claiming to be room sealed (I know, claims and reality ...). I definitely want a wood burner in my new build and I assumed that room-sealed would be relatively easy to both find and install. Have you changed your opinion since writing here ? Do you believe that there are some (good, reliable, well designed) room-sealed stoves around ?

  11. It's all true about wood prices and renewability, but aren't we forgetting these stoves are not all just wood burners - many are "multi-fuel" meaning you don't just have to burn wood?

    My company encourage the burning of smokeless fuels in those areas covered by clean air legislation, and since large tracts of the UK fall under this banner, the amount of wood being burned shouldn't be quite as high as it is!

    We'd welcome your views and comments on fuels on our forum as our customers often ask us for advice about this..


  12. Wood burning stoves are quite popular in more and more city homes, but have always been popular in the rural community. With rising oil and fuel prices wood provides a considered alternative. I've recently sourced a wood burning stove through Less Lettuce and have installed it as a feature in my main living room which is great to gather around during the wintry nights.

  13. There are many different terms for different types of stoves, firstly when talking about Wood Burning Stoves, Log Burners or Wood Burners that often refers to stoves as a collective term including stoves that burn wood, coal and/or smokeless fuel.

    wood burning stoves

  14. They have now abandoned the technology (for the time being) and are concentrating on wood-fueled boilers, like....

  15. We have a stovax and love it. Most stoves around here are gas and i just like the vibe of real wood burning. We do have faux wood beams in our house though!