Compost Heat Recovery

Fuel, Food, Fertility 

As our passion for compost has grown at Emerald Spirit Botanicals, we have explored the concept of capturing heat from compost and using it to heat water. Over the ’16-’17 winter, we ran our first trial on a compost heated greenhouse. The results were somewhat successful and, as with all first runs, we have learned some new lessons to improve the design.


In early spring, we start our cannabis from seed and heat our greenhouse with propane to ensure a strong start for this heat loving crop. In previous years we ran two propane heaters almost every night to keep the greenhouse at a favorable temperature for our starts. Needless to say, this used a considerable amount of propane. One of our farmers studied compost heat recovery in college and was eager to apply his research to a compost heated greenhouse.

This compost pile was made of a mixture of wood chips, manure, and fresh plant material. 500′ of PEX tubing was woven through the compost as it was constructed. The PEX was then coupled into poly tubing which ran into the greenhouse and underneath the seed starts. Within a week the pile was up to 140F. Water was circulating through the system above 100F leaving the pipes hot to the touch. Although this system was unable to heat the entire greenhouse sufficiently for the plants, it reduced our propane use in half. The compost effectively served as a fuel source to heat our greenhouse.


As the compost cooled below 100F, it was inoculated with mycelium of Stropharia rugosoannulata, commonly know as Garden Giant, or Red Wine Cap. Throughout the summer we have been maintaining a moist environment in the compost pile to allow the mycelium to spread throughout the pile producing a food source during the rainy season.


As the wood chips are broken down, they offer a perfect mulch for our growing orchard. This material can then be added to our orchard and act as not only a source of fertility, but as a sort of seed for the Stropharia to become established throughout our perennial gardens.