They have been done. Dangerously! There are YouTubes.
But all that I have seen are terrible kludges. There's more to making a safe water heater or boiler than lay people realize. (I'm speaking as a licensed master plumber, and as an engineering degree holder.)
Here are some Youtube's that I like:
https://www.youtube.com/watch?v=9bU-I2ZiML0 (Mythbuster's water heater)
People have tried to discuss them there, and always ended up proposing unsafe things. So . . . I'm not allowing those discussions.
Sorry, but thread closed!
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