You would need a non-mixing heat exchanger and an air stream from your compost exhaust that runs against a stream from the house. The delta in temperature, however, is unlikely to be high enough that you will be able to extract much heat from it. I’m not sure how much energy is given off by aerobic composting, except that under ideal conditions it is enough that a large pile could get hot enough to kill all but the most thermophilic microbes.
