It’s just a heat exchanger glycol loop that uses burning wood to generate the heat, very similar to a gas-fired boiler. With a large enough burner you can have

It’s just a heat exchanger glycol loop that uses burning wood to generate the heat, very similar to a gas-fired boiler. With a large enough burner you can have multiple heat exchangers or multiple glycol loops with a large heat exchanger for multiple buildings, similar to how commercial buildings use a single boiler or chiller to heat/cool large buildings or multiple buildings that need multiple heating or cooling glycol loops. Most of the houses that burn wood for heat in the US are in sparsely populated rural areas where sharing a burner wouldn’t make sense due to the loop length and pumps needed to circulate the glycol. Densely populated areas in the US that need lots of winter heating generally have natural gas distribution networks.