1st experiments were just off the shelf compost tumbler style composting.
Didn't work well for me.
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Smallest Compost heater experiment was small
~4 Gallons in a old ~5 Gallon water bottle , in my basement.
pic attached
It didn't make enough heat to create a noticable dT from ambient .. but did compost some of the material over a ~6 Months potential heating season.
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Then I tried 6 different mixes , each ~40 Gallons in it's own ~55Gallon Drum.
Also in my basement .. exhaust gases vented out through old (not in use) natural gas water heater chimney flue.
pic attached.
video
https://youtu.be/dRHOkPpzCaM
Better results , but not good enough.
logged data graph attached.
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This 2020 winter I started the 3rd test / experiment outside in back yard ~600Gallon total.
It's been doing better so far than the 2nd test .. but , there are still some improvements I have planned for a 4th version in the fall/winter of 2021.
Pic attached
Video
https://youtu.be/fpaYgWquZCI