The Fuelwood Heater is a Heater that generates heat by burning items and lava from lava buckets. Lava cannot be piped into the Fuelwood heaters. It can not burn fluids other than lava, and it cannot connect to Mechanical Pipes
It can be used to indirectly power a Heat Generator, but at severe loss of energy. It's usage is best seen when providing a Thermoelectric Boiler with Heat, and for further factorization, it is advised supplying the Fuelwood Heater with charcoal from an automatic tree farm.