I remember reading that burning propane yields 21,000 BTU
per pound. Not sure about butane. Much the same, I'd guess.

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Christopher A. Young
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"Dave Liquorice" wrote in
message
ll.co.uk...

Each kg of gas burnt produces a kg of water. But a kg of gas
yields
quite a bit of energy. 10kW springs or there abouts springs
to mind
so a fire running at a couple of kWhr output isn't a great
generator
of moisture, a cup full/hour ish.