Hi Don,
I'm so sorry I never replied to this last post of yours - this is really bad and I do apologize. It must have slipped my mind at the time, and then other things took over and I forgot all about it.
I thank you very much for your detailed reply to my question, and although we haven't started yet we're still wanting to get both going - a shower and a hot tub; the shower probably soon.
Your friends' bath ideas seem great, and I'm sure we'll use them to work something out for ourselves.
Thanks again,
Carola
Don McLean wrote:Hi Carola, no, no experience of heating a hot tub this way.
I guess if you set a bath in (or built a large compost heap around) a tub of some sort, & heavily insulated the top of the tub (to prevent heat loss), water in the tub would heat up over time, ultimately to whatever the temperature of the compost heap was.
A typical bath is aroudn 100 litres or so of water, a significant volume to heat, i.e. it would heat relatively slowly. The original show compst heap appears to have heated much more than this over its 2 month life though, so it should be possible. I guess you may need something in the water to prevent hot-water loving things growing in the lush-temperature water as it heated up. Epsom Salts maybe???
I've friends who removed the spiral copper heat exchanger from inside a typical (UK) copper hot water cylinder, and cobbled this (somehow; I can ask them if you are interested) to a tub of some description to make a hot tub. They just filled the empty centre of the copper coil with wood, lit it and the hot water naturally gravity circulated (thermosyphoned) to the top of the tub; with a lower, return water connection in the tub (possibly via the plg hole) for the (cooler) water to circulate back to the coil to be re-heated by the fire. Appropriate relative levels are ctircal for an efficient thermosyphoning system.
The simpler solution is a (heavy guage) tin bath directly over a fire. There was an article about this type somewhere on the Permaculture UK site recently (2011, via a Facebook notification), though all I could see just now was: http://www.permaculture.co.uk/issue/summer-2006.
Cheers, Don
