I'm not paying to heat that much water just so I can soak.
A person could heat a hot tub with a Biochar+Energy System and make money doing it...
In case you just sneezed "horsesh!t" under your breath, heating 200 gallons of water with a temperature rise of 55 degrees F using a biochar making heater would consume about a dollar's worth of pellets and make about four dollars worth of biochar.
It would also sequester some 15 pounds of atmospheric CO2, if you put it in your garden.
“You never change things by fighting the existing reality.
To change something, build a new model that makes the old model obsolete.”
– R. Buckminster Fuller