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Heat and Cooking From Wood

Seasoning, stoves, chimneys and the law

How much wood a year really is

A small well-insulated house heated by one efficient stove burns roughly 3 to 5 cubic metres of stacked seasoned hardwood a year in a mild climate, and 8 to 15 in a cold one or a draughty stone house. Cooking on wood adds more. That is not an afternoon of work: cutting, splitting, hauling and stacking a winter's wood is several full days of physical labour, repeated every year, plus the cost of a saw, fuel, chains and protective kit. Buying it delivered in Portugal typically runs tens of euros per stacked cubic metre and varies hugely by region and species.

Seasoning and moisture content

Fresh-cut wood is around half water. Burning it wastes most of the heat boiling that water off, fills the flue with tar and blackens the glass. Split it soon after felling, because bark stops drying, and give it time: 6 to 12 months for softwood, 12 to 24 months for dense hardwood like oak and olive. The target is under 20 percent moisture, measured with a cheap pin meter on a freshly split face, not on the outside of the log. Dry wood is lighter, rings rather than thuds when two pieces knock together, and often shows cracks across the end grain.

Stacking and stove efficiency

Stack off the ground on pallets or rails, in single rows with gaps for air, ends exposed to sun and prevailing wind, with a cover over the top only. A tarp down the sides traps moisture and grows mould. Keep the stack away from the house walls because it houses insects and rodents. On the stove itself: an open fireplace returns perhaps 10 to 20 percent of the wood's energy to the room, a modern closed stove 70 to 80 percent. Burn hot and bright with the air open rather than damping it down overnight, which is exactly what coats a flue in creosote.

Chimneys, creosote and sweeping

Creosote is condensed tar from cool smoke, and it burns. A chimney fire roars like a jet, throws flame from the pot and can reach 1000 degrees Celsius, cracking the flue and setting the roof alight. Prevent it: burn dry wood hot, and have the chimney swept at least once a year, twice if you burn resinous softwood or use the stove daily. Fit a spark arrestor where roofs and countryside are dry. If a chimney fire starts, close the stove air, get everyone out, call the emergency number, and do not throw water up the flue. Keep a working extinguisher near the stove.

Carbon monoxide and the Portuguese rules

Carbon monoxide has no smell, no colour and no taste, and it kills people asleep in their beds every winter from blocked flues, poorly fitted stoves and generators or braziers used indoors. Fit an audible CO alarm to the standard in every room with a burning appliance and outside the bedrooms, and test it monthly. Separately, learn the law: in Portugal burning of cut vegetation and agricultural piles is restricted and usually banned outright during the critical fire period, roughly July to September, and cutting certain trees such as cork oak and holm oak requires authorisation. ICNF and your camara municipal hold the current rules.

Next lesson: Keeping Food Without Electricity →

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