I make my biochar during the winter near the arctic circle by heating my home with firewood. About 4 cubic meters per winter for a 100m3 house.
My log burner is a Pönttöuuni RMH batch box with waterback that has no grate or under air, the fire burns flat on firebricks. I burn about 1 to 1.5 buckets per day. I usually burn 1 batch log stuffed firebox morning and evening, mid day when it is real cold.
Once the wood gas flames have all burned out, I shutoff all intake air into the wood stove and close the chimney damper to 10% open; snuffing out the glowing charcoal bed. Once the heat and glow in the charcoal bed has diminished I close the chimney damper 100% and let things continue to extinguish until the next load and firing.
I clean the firebox at the beginning each firing to harvest the char. Placing the ash and charcoal into a sealed metal ash bucket. A day later after the bucket is filled and all embers are extinguished; It is then sifted to separate the ash, crushed in a low speed chipper and fed into the basement rotating vermicomposter.
With this procedure I get a warm home and hot showers from the wood gas flair and about 1m3 of rich biochar vermicompost every winter for my garden.
During the winter I use this charpost in trays with professional LED grow lamps in a ladybug infested mylar tent to grow fresh herbs and salad all winter long. The maths show my salad doing this is about >5x cheaper than the store accounting for the lamps, with flavor and nutrients no store sells.
Come spring I lift out the root balls in the trays into my hugel raised garden beds making a very instant summer garden for our short growing season.
The sifted ash fraction is mixed into the garden watering jugs periodically over the summer to water in phosphorus, calcium, and it's other minerals to boost my fruit production and prevent blossom end rot.
