This society consists of various peoples and fantasy races, but most of them have heat requirements similar to humans. What would a reliable source of heat for this society be? Bonus points if this heat also provides light.

Additional Info...

  • Approximately 8000-10,000 feet (2.5 - 3 km) under water on the ocean floor.

  • Everything is surrounded and covered by water.

  • Natives have gills and need to "breath" the water.

  • They have visitors and tourists that aren't adjusted to the ocean depths and need additional compensation (not a seperate question, just a note for the requirements).

  • The output area for the heat needs to be relatively safe.

  • We'll focus on city areas which are vaguely similar to modern "big" cities (ie skyscrapers, city layout, etc).

  • Technology level is that of the "Advanced Ancient Acropolis". http://tvtropes.org/pmwiki/pmwiki.php/Main/AdvancedAncientAcropolis

Edit - The duplicate suggestion, while certainly containing useful information, doesn't address the question on the same scale required for this question.

  • $\begingroup$ That deep underwater? Volcanos or dead biomass from above, maybe in methane form $\endgroup$
    – Raditz_35
    Commented Jun 20, 2017 at 15:52
  • 1
    $\begingroup$ This is a dupe, give me a minute. $\endgroup$ Commented Jun 20, 2017 at 15:53
  • $\begingroup$ Is it the case that this source of energy can be moved? $\endgroup$
    – ifly6
    Commented Jun 20, 2017 at 21:39

2 Answers 2


An answer that exists in nature: hydrothermal vents.

Water emerges from these vents at temperatures ranging from 60 °C (140 °F) up to as high as 464 °C (867 °F).

The pressure from high-temp vents could be directed into pipes to allow controlled heating of spaces throughout a city, with excess heat/pressure being bled off outside the city.

These vents, and the magma systems that heat them, are a potential heat source as well as a potential source of minerals.

  • 1
    $\begingroup$ Not just that but the heat and pressure differentials are a potential source of mechanical power, through something as simple as a Stirling heat engine, for the purpose of driving mechanical pumps, circulation of fresh water, waste disposal systems and other more commercial enterprises like mechanical transportation and delivery; e.g. an underwater trolley system. Why swim for miles when the trolley can get you there in a few minutes? $\endgroup$
    – Amadeus
    Commented Jun 20, 2017 at 16:16

What you need is a source of heat that could survive underwater. A few ideas come to mind.

Plasma. Plasma would not need to consume oxygen to heat things up. A device that could heat up fuel to plasma state isn't too far from reality. In fact, we've been using such things in metal machining. Though it might burn too hot.

Lasers. Lasers, if powerful enough and concentrated, can burn through metals. This one has an advantage of being more controllable. as you can choose how much power you're putting into the laser.


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