Brian Knight

The biggest concern to me is spreading diseases and invasive bugs and plants. On-site sources are definitely preferred, the closer the better.

Inspired by this thread I started my own dedicated leaf mold pile recently. Potential problem though, its getting hot!

I usually add coffee grounds to my leaves for compost, but after reading this thread and encountering what indeed seemed to be a different product with older, bagged leaves set aside for my compost water heater I wanted in on more of the mold action.

Maybe its the volume, a 5' diameter by 5' tall well compacted and moistened leaf pile. The heat definitely took longer to form and is not getting as hot but several weeks after creating a leaf-only pile, Iam getting temperatures close to 100F! I measured at the end of a cold snap with almost a week of sub-freezing outdoor air temps.

I absolutely did not include ANY extra nitrogen sources in this leaf pile. Its all bagged leaves from the neighborhood and sometimes small amounts of grass makes it in but seems an unlikely amount to make a difference. I did not see any to remove when making it. Anyone else getting such high temperatures with leaves only? I wanted leaf mold, which I have experienced in piles of separated/bagged leaves, not more compost! Iam thinking looser piles may be better. Thoughts?

Here is my Compost Water Heater thats tied directly into my home's main plumbing system.

No way Scott, that absolutely needs to be pointed out. These piles give off stuff that is not safe to breathe on a regular basis. Any direct heating needs to be done very carefully in terms of air quality.

Here is an indirect method that could be applied to small homes with good thermal envelopes. I think it would be relatively easy to extend this style compost water heater into a radiant floor application. Whats really exciting is that if the "cold" floor is above the warm compost, you could probably get it to thermosiphon with no circulators needed.

Found this Ben Falk compost water heater video but couldnt find anything on he did on space heating but didnt look very long either.

I think heating a house with compost is possible but not easy. Ive heard of Chris's method for barns (piling compost against masonry foundation) and think small homes could do the same thing. It seems the safest way would use tubing with water with a clear separation of home and compost and the moisture and other unhealthy gases associated with decomposition.

While it would be important to make large volumes of compost and use the heat efficiently, the bigger variable to me is the size and efficiency of the home. Tiny homes certainly have the most potential and I imagine they could do pretty well even with relatively low levels of insulation.

For most homes its all about the thermal envelope: airtight, continuously insulated and modest levels of good performing fenestration. With a passive house or net-zero levels of efficiency, it doesnt take nearly as many BTUS to keep the home warm and comfortable.

Ive been thinking of how a home could use compost for space heating without the complications of plumbing and Iam picturing something similar to what Chris describes for the small Wofati. I also picture a home on piers with enough head room below to maintain big compost piles. This is a more dangerous approach and would require meticulous airtight construction for the floor and probably a strong vapor barrier there as well. The only thing that has me wondering is how much to vent down there to keep things safe yet not allow too much heat to escape.

I agree with Troy there and extend the de-humidification aspects to the earth tubes. They may lower the temperature of the incoming outdoor air but they will probably not effect the humidity in any meaningful way. As you may know, AC makes things more comfortable with Sensible (air temp) and Latent (humidity) conditioning.

The temps effected would depend on a number of variables: Outdoor air temp, ground temperature, CFM through tube, length of tube, diameter of tube.

Gabe! Welcome to permies. Lots of threads here on earth tubes if you poke around. I dont think you can do any meaningful "heating/cooling" with earthtubes unless you have very low expectations. At best, you can temper your incoming outdoor air ventilation.

Some people in dry climates seem to do alright with these systems but in more humid climates, they are more risky and need to include a well thought out way of cleaning the interior surfaces of the tubes.