Off-grid livers and permaculture gardeners have developed a fascinating range of techniques for heating polytunnels and other growing areas in cold-weather climates. Some other ideas for keeping your polytunnel warm in winter can be found here. Many polytunnel gardeners create hot beds using decomposing straw. Others run solar heated water through their polytunnels. A third option is to use solid fuel heating – a more eco-friendly alternative to diesel or oil heaters, and an alternative that can yield temperatures that are reliably higher than those that can be achieved with renewable electricity options in the UK. Creating a rocket mass stove to heat a polytunnel or another growing area is one of the most efficient options around.
Isn’t It Dangerous To Have Flames Around A Polytunnel?
Of course the answer to this is yes, it can be. While some gardeners do take care and safely use a stove inside a polytunnel, the safest choice is probably to build a rocket stove close to a polytunnel but outside and to use the exhaust pipe of the stove, buried a safe depth under the soil, to increase the temperature of growing areas. However, rocket mass stoves are a safer and more contained option than other solid fuel heaters, and are used as space heaters inside many homes, sheds, garden buildings, greenhouses and polytunnels. You should always take a lot of care, and ensure adequate ventilation whenever any burning is taking place.
What is a Rocket Mass Stove?
Understanding why it is possible to have intense heat and combustion inside or close to a polytunnel involves getting a basic understanding of what a rocket mass stove is, and how it operates. A rocket mass stove is a type of rocket stove (an efficient wood burner) which has incorporated ideas the of a masonry heater.
These burners have an insulated combustion chamber where wood is burned with high efficiency at high temperatures, and an exhaust pipe in contact with a large thermal mass which absorbs most of the heat generated before it is released into the atmosphere. The J-shaped design of the fire box and chimney mean that wood is burned hot and clean – the fire burns sideways and with a much higher efficiency than a regular wood burning stove, so little smoke is created. Often, these stoves can be run using just sticks, twigs and pruning materials from elsewhere in your garden.
Types of Rocket Mass Stove
Various different designs have been created and the refined ideas can be one of the most eco-friendly and cost-effective ways to heat a space. The heat from the exhaust can be used to warm a growing area or a bench seat for sitting on or for germinating seeds.
Often, rocket mass stoves are self-built, though there are also some shippable cores on the market that offer an easier route. Whether building or buying, the proportions and exact design of a rocket mass stove must be carefully worked out in order for the heater to work safely and as it should.
Surprisingly safe, cheap and efficient, a rocket mass stove could be the perfect solution for heating your polytunnel. If you need something more than the heat of decomposing straw and want to be able to heat your polytunnel beds or seating areas to a higher temperature during the winter, one of these could be a sustainable solution.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.