Is there any heat energy lost to the mechanical force of pushing a piston in a combustion engine?

In other words, would a natural gas burning as a flame produce more heat than the same amount of natural gas that was burned when driving a combustion engine?

The context of this question is around fuel efficiency of natural gas water boilers.

My current understanding is that a naked natural gas flame is burning inside the unit, and heats water that is contained within a series of pipes, which in turn is cooled in a heat exchanger, and that same heat exchanger heats the incoming cool water.

I'm wondering, would if it make any sense at all to burn that natural gas inside a combustion engine and use the heat of the combustion engine used to heat the water to the same extent as a naked flame.

More generally my goal is to solve the question, can we heat water the same extent by burning the same amount of natural gas and get free mechanical energy?



1 Answer 1


Check out combined heat and power systems... generates electricity and makes use of the waste heat to heat water - but is only really efficient when there is sufficient hot water demand ie heating load.

  • $\begingroup$ this looks to be exactly the kind of appliance that I was dreaming of! Thanks! I'd like to upvote your response but I have too few reputation points at the moment $\endgroup$ Commented Nov 18, 2019 at 15:03
  • $\begingroup$ You can use the check mark to accept the answer if you wish... $\endgroup$
    – Solar Mike
    Commented Nov 18, 2019 at 16:21
  • $\begingroup$ Good answer Solar Mike! $\endgroup$ Commented Nov 19, 2019 at 8:15

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