Just outside the tiny village of Spinningdale, on the north shore of the Dornoch Firth, about 50 miles (80 km.) north of Inverness lie Ledmore and Migdale Woods, a conservation area owned by The Woodland Trust. Here, environmental scientist Jim Monahan, his wife Jo, a local teacher, and their son Magnus are building a sustainable family home called Rowangarth.
Jim designed the house himself and has been building it (with help!) for the past three years.
The building is a "passive solar" design is based around a traditional, post and beam, “green” timber frame enclosed within a “breathing” wall and roof construction incorporating natural hemp and sheep's wool insulation. High levels of thermal mass have been included in the form of solid, unfired clay brick internal walls, plastered with clay and lime render, a limecrete floor screed (containing underfloor heating pipes) and a Finnish-style "masonry heater" (see below).
There is also a fully-equipped carpentry workshop with self-catering accommodation upstairs.
The project is almost finished and Jim and his family hope to move in this autumn.
The major remaining tasks include:
laying hand-made terracotta floor tiles and Caithness flagstones on the ground floor using lime mortar;
laying flooring machined in our workshop from recycled Douglas Fir sarking boards;
installing a wood-burning cooker, solar panels and a thermal store;
and building a "trombe wall" conservatory.
If you are interested in learning more about sustainable building techniques and materials, we have opportunities for volunteers and/or paid workers to help with the project. We can provide accommodation.
For further information contact Jim Monahan by telephone on 01862 881259 (from within the UK) or +44 1862 881259 (from outside the UK), or email firstname.lastname@example.org
In October 2005 a week-long workshop was held, led by stove mason, Sten Sjöstrand, assisted by Jim Monahan and Malachy Reynolds
During the course, participants were introduced to the basic principles of masonry heater theory, design, construction and operation. The internal structure of a masonry heater is quite complex and is best understood by building one. The core elements of a Finnish "contraflow" heater incorporating a bakeoven were constructed. Activities included working with firebricks and refractory cement, using ceramic fibre material, making pre-cast elements in moulds using "castable" mix and installing hardware (fire-box and bakeoven doors, cleanouts etc.).
Some pictures from the course give a flavour of what it was like:
What is a Masonry Heater?
Most masonry heaters are intended for burning wood, but they were historically designed to burn almost any type of solid fuel. They use a small, intense fire that is lit once or twice a day, depending on heating requirements. As the hot combustion gases from the fire pass through the network of smoke channels, the masonry absorbs much of the heat, which then is radiated slowly and steadily into the home over the next 18 to 24 hours.
Wood burning masonry heaters are much more efficient and clean burning than conventional wood burning fireplaces. A combustion efficiency of close to 90% is common (as opposed to 60% for a regular wood stove and 10% for a regular fireplace.) The relatively small, but intense fire also results in very little air pollution and very little creosote build-up in the chimney. If you burn dry wood rapidly, it is a very clean fuel. If you try to burn it too slowly, the fire changes from flaming to smouldering combustion. The burning process is then incomplete, producing tars and increasing atmospheric pollution dramatically. This is a common problem with wood-burning stoves which are often damped down (i.e. starved of air) to slow fuel combustion (for example, to keep them going overnight).
Because most of the heat from the fuel is transferred to the masonry and slowly released into the room over the day, this type of heater does not need to be loaded with fuel as often as other types of wood heating appliances. In addition, if the masonry heater is built where sunlight can directly shine on it in the winter, it will increase the "thermal mass" of the house absorbing the sun's heat during the day and releasing it slowly into the room during the evening and overnight. This is an important advantage if you are planning an energy-efficient house. The average energy demand of your house will be quite low. For most of the time, it may require only 1 to 2 kW of heat. For most conventional woodstoves, this is below their “critical burn rate”, or the point where they start to smoulder. Masonry heaters fit the bill perfectly. If you need even a very small amount of heat, such as between seasons when you simply want to take off the chill, you simply burn a smaller fuel charge - but still burn it quickly.
The surface of a masonry heater never gets too hot to touch. Since it gives out radiant heat, like the sun, it warms what it "sees". You feel comfortable at lower air temperatures thereby reducing health and allergy problems associated with dry air and airborne dust carried by convection currents.
Below are pictures of various examples of heaters from the websites of some of the many masonry heater firms in the U.S. and Canada.
For further information on masonry heaters visit www.mha-net.org the website of the Masonry Heater Association of North America. It is an excellent portal with links to lots of other sites.