Written by Nick Hills for the Association for Environment-Conscious Building’s “Building for a Future” magazine a couple of years ago………………….
I first came upon these stoves about fifteen years ago, in a previous incarnation that required me to spend my winters in central Norway. I was attracted, initially, by their aesthetics and it seemed to me that there was an untapped market here in the UK, a thought that was reinforced when I found an article in World of Interiors magazine shortly afterwards that heaped praise upon their beauty and elegance but provided few clues as to their source. It was only when I dug deeper that I discovered that their beauty is far more than skin deep.
The Scandinavian ceramic stove is normally constructed in its simplest form, that is as a space heater designed to perform that one function very efficiently. Tests in Swedish government research laboratories have rated the heating efficiency of these stoves at over 90% and their environmental efficiency at over 80%. They have been granted exemption from the Clean Air Act in this country due to their extraordinary ability to consume practically all of the pollutant normally produced by burning wood and this without the use of a catalytic conversion system.
Their impressive heating efficiency is a product of the same factors that allow the stove to consume the pollutants; the high temperature in the combustion chamber, the channelling of the hot smoke and gases around the interior of the stove instead of straight up the chimney, the use of stone with a high heat-retention value and slow release rate and the employment of a damper to keep the heat in once the fire has gone out.
The burning cycle differs from conventional stoves in that the fire is alight for relatively short periods of time, generally a couple of hours. During this period, the wood is being consumed at maximum efficiency with normal combustion temperatures of around 1,000°C. The fire is then allowed to go out and the damper closed (the Scandinavians close theirs completely, but in this country where we are less familiar with the concept we are required to construct a damper that will only close to 80/90% to allow for the escape of any residual fumes).
So the fire is either roaring away like a furnace or it’s out, thus avoiding the smouldering cycle that is inherent in the design of many conventional woodburners, which is both inefficient and produces so much pollutant. The heat stored in the stone and tile mass is then released in the form of long-wave radiant heat until the stove reaches ambient temperature or until it is re-fired.
The length of time that the stove retains useful heat depends on its size (mass) and the ambient temperature, but a stove that was alight in the evening will still be warm the following morning and some large European stoves are capable of retaining heat for 30 hours; it goes without saying that more heat gain will be felt in a well insulated building.
Stoves built in houses with a lot of brick and stone construction also heat the fabric of the building itself which will contribute to the heat storage capacity, but well-insulated houses of wooden construction have also been found to have benefited from the inclusion of a high-mass stove in the heating plan. This stove would normally be built on its own foundation and travel right up through the house very much as a conventional chimneybreast would.
This produces a core of comfortable heat as near to the centre of the house as feasible with the possible inclusion of hotplates, ovens and a warm seat upstairs in a bedroom or bathroom.
As a general rule of thumb a ceramic stove of average dimensions (about 2m high and 80cm in diameter) will heat about 150m3, in return for a daily burn of about 15kg of wood. This is such an effective use of biomass that over 90% of new Finnish homes have a ceramic stove of some sort.
Although most of the prefabricated designs we are currently producing and building in this country are derived from the Scandinavian model, ie., a vertical five-channel system, other variations can be built to suit specific requirements using, in some cases, components from Europe. In addition, fireboxes can be built specifically for the burning of coppiced wood, either standing vertically or laying horizontally as faggots.
A Ceramic Stove represents a golden opportunity to explore avenues other than the conventional (in this country) choice of an open fireplace, an iron stove, electric storage heaters or central heating (be it gas or oil-fired), each with its own negative aspect;
a fireplace is barely 10% efficient and will wick heat up the chimney even when the fire is out;
iron stoves can be soporific, produce pollution when on slow-burn and toxins when dust settles on their hot surfaces (as long ago as 1920, Dr Leonidas Gimbutas wrote in Lithuania “Such stoves burn dust or anything on their surface and spoil the air with a bad smell.”);
electric storage heaters use energy that has been produced elsewhere, so pollution is displaced;
hydrous systems can be intrusive and noisy (how many of us have become accustomed to the groaning of the pipes before the alarm goes off in the morning), radiators are seldom easy on the eye and there is a growing number of people who feel uncomfortable surrounded by continuously pumped water;
oil & gas will run out sooner or later and their use contributes to the Greenhouse Effect whilst burning managed wood is CO2 neutral.
In addition, those who opt for a Ceramic Stove can express themselves visually in ways that they had probably not dreamt of. Octagonal Osier stoves made in Brittany (by an ex-pat from Gloucestershire), elegant stoves in the Swedish Gustavian style, exuberant stoves from Bavaria, rustic stoves, cookstoves, bread ovens, combinations and even a stove that appears to be a wall are all possible and we are more than happy to discuss clients’ requirements at length with them. At the time of writing, I have just returned from a site visit in Athens and I’m looking forward to another in Atlanta.
“But what about the fuel?” I hear you ask. “Where am I going to get the huge amounts of wood needed to feed the voracious appetite of a large woodburner?” Well, firstly, the stove’s appetite has deliberately been kept as small as possible and was one of the criteria decided by the King of Sweden in 1767 when he commissioned Barons Cronstedt & Wrede to design a stove that would burn more efficiently and save his forests.
Secondly, the stove will happily burn any type of wood you feed it, regardless of species, as long as it is dry and seasoned. We regularly burn offcuts from a nearby sawmill and unrecyclable wooden packaging from local retailers.
Thirdly, you may be in a position to grow your own. We have designed an extended firebox specifically (but not exclusively) for the burning of faggots (bundles of coppiced wood, commonly fast-growing willow or poplar) and the owner of one of these simply inserts one of his home-grown faggots, lights the thin end, closes the door and walks away.
To quote Mark Twain “At half-past seven on a cold morning the servant brings a small basketful of slender pine sticks and puts half of these in, lights them with a match and closes the door. They burn out in ten or twelve minutes. He then puts in the rest and locks the door. The work is done. All day long and until past midnight all parts of the room will be delightfully warm and comfortable. The stove’s surface is not hot; you can put your hand on it anywhere and not get burnt”.
Fourthly, the availability of wood as fuel is increasing all the time as suppliers recognise that there is a growing market that, in turn, acknowledges that it is OK to burn wood that has been grown for that purpose and is being replenished, or waste from the manufacture of furniture, for example, in the form of pressed sawdust briquettes.
Projects Past & Present
The following case studies illustrate some of the range & diversity of these astonishing stoves.
The National Trust’s requirement was for an ecologically sound heatsource that would provide safe, sustainable heat in their educational facility. The Osier met all their criteria, enabled them to burn offcuts & thinnings from this and other sites with no danger to children from hot metal surfaces.
Old Swedish Stove (Helsingborg)
Recycling at its best! Take an old stove out of a building that is due to be demolished and rebuild it with a new interior and a new lease of life. The traditional building method, using just clay and sand, means that this can be done time and again.
New Swedish Stove (Lincolnshire)
Another new lease of life, this time for the building, brought into residential use, as many are in our increasingly secular society. This stove is no reproduction, but part of a continuous line of development. However, it retains the classic five-channel flue system developed in 1767 (as does the Osier, above).
New Bavarian Stove (Surrey)
And now for something completely different! The brief here was to build a monolithic stove, with the fire visible from both sides and incorporating a low dividing wall, a bench and a staircase. Co-operation with Simon Clark from Constructive Individuals, Stairflight and a German colleague brought it all to fruition. The approach here was to use a Bavarian “einsatz” as the primary source of heat, this being placed inside the wrap-around staircase, with an exterior shell of heat-retaining, conductive “chamotte” plate, also from Bavaria. The result was a stunning, effective source of heat for a modern, light-filled house.
Latvian Combo (Pyrenees)
Another co-operative effort, this time with some Latvian colleagues, one of whom I had met the year before on a fact-finding trip when I stayed in his home in Liepaja, an old port and erstwhile Russian naval base. The brief this time, from our clients, an English film-maker and his Polish wife, was for an organic stove in their Pyrenean farmhouse, that would include a hotplate, boiler, oven and space-heater over two floors. My Latvian friend, Juris, had the component parts required fabricated at home in Latvia, including the moulding tiles that we incorporated into the design. We set off in two vans, one from Oxford, one from Liepaja and on arrival carted the 3.5 tonnes of material almost a kilometre up a mountain track in wheelbarrows. We soon settled into a routine, with two men building the stove, the other two on the wheelbarrow team bringing up fresh supplies of tiles, clay and sand. Eight hard August days later, our clients had their handbuilt, terracotta, four metre, four-function stove standing in their living room, upstairs study and bedroom.
Our client has experienced problems with the existing open fireplace since the house was built, due mostly to the imbalance in the volume of the two spaces served by the fire. We propose to replace this fireplace with a stove similar to the stove in the chapel, above.
Our client here is a large corporation, currently refurbishing an old dairy farm to be used as a girls’ retreat and summer camp. They are purchasing a couple of magnificent old stoves to be rebuilt on site. This one, laid out for cleaning and viewing, will be rebuilt in its own niche and will stand at about 3.3m tall.
Hebden Bridge, Yorkshire
Another eco-project under the watchful eyes of Peter Warm and Gaia’s Andrew Yeats; we plan to combine some of the features of several of the stoves above. The proposal is for a cylindrical stove, 3 metres tall, 1100mm in diameter, handbuilt in traditional fashion from Latvian tiles, made to order to the required radius. The finished structure will be limewashed or painted with ecologically sound or neutral paint, if required.
I believe that these stoves, in all their disparate forms have a significant rôle to play in the quest for lower household emissions of CO2, toxins and particulates. Our website has been described as evangelical and I make no apology for that. I also believe that more people would embrace this technology if a way could be found to disseminate the information contained in this article, and a lot more besides, more effectively. Whilst I have attempted to cover just some of the wide spectrum of stove designs available, I am convinced that the Osier, designed and developed in Gloucestershire, now made in France, is the ideal vehicle to further the adoption of the generic ceramic stove in countries such as the UK that do not have them as part of their culture. If any fellow AECB members would like to assist me in hastening the development of the ceramic stove industry in this country, I would love to hear from them.