https://permies.com/forums/similars/similarTo/144198/rocket-powered-hot-tub-plumbing
Make a rocket powered hot tub - plumbing.straw.rockettub PEP BB - Similar Threads
In this Badge Bit, you will make a hot tub powered by a rocket! - evidence of heating water from under 60F to 105F in under an hour (or 70F to 105F in 45 min)...
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