It is refreshing to take a cool shower in hot weather. And for the sake of discussion, lets assume that one should be "comfortable" with temeratures when taking a shower.

Considering that the vast majority of the heat from a shower is lost down the drain, would it not be more energy efficient to heat a confined space (shower stall) to a temperature that would allow you to shower with cool water rather than hot?

How hot would it have to be in the room for 70 degree water to be "nice." 60 degree?

And since all of the energy used to heat the air in the space would remain in the space/room, would you use less energy to take a comfortable shower doing it that way?

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    You would do far better heating the air so you can split your shower into three stages: wet yourself, turn the water off to apply soap and shampoo, turn the water on to rinse off. If you're having 20 minute showers it may be better to buy a small indoor swimming pool (or Japanese Bath) and store hot water in that.
    – Ⴖuі
    Jan 27, 2016 at 7:07
  • I agree that for total energy savings and water conservation, staged showering would be the way to go. But unfortunately most people won't do this. Nowadays I'm in the same boat, though I did do just that when I served in the Peace Corps in the mountains of Bolivia with only frigid water coming from the tap.
    – That Idiot
    Jan 27, 2016 at 12:34
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    In the winter, close the drain (assuming you have a tub/shower, and let the hot water stay there until it reaches room temperature. Also helps humidify the air in dry climates.
    – jamesqf
    Mar 12, 2016 at 3:44

2 Answers 2


OK. Since asking this question I've tried to come up with an answer - or at least a back of the envelope calculation:

According to a steam shower vendor, a 10KW unit is required to provide enough steam at 118 deg.F in a 6'x8'x 8' enclosure. The timer runs for 20 minutes (about right for a nice shower), so figure the unit would use 3.3KW and 2 gallons of water to make the steam room hot and steamy.

According to numbers pulled from all over, figure an average 20 min shower uses 50 gallons of water (416.5 lbs.), and that in my area that water comes out of the ground at 55 degrees F. To heat that water to 110 deg.F would take approx 22,910 BTU.

Converting KW to BTU (and here are the limits of my understanding - please correct my conversions/assumptions as needed) it looks like 3.3KW is about 11,260 BTU.

If this is all reasonable, then heating the shower to 82.5 deg.F would require 11,500 BTU, which, when added to the 11,260 BTU for the steam would total 22,760 BTU - or slightly less than just running the hot shower by itself. If you could go with heating the shower water even less,then the savings would appear to increase.

I am fully aware that this answer is full of broad assumptions, simplifications, and perhaps misunderstandings.

  • The OP asks for heating a confined space. You translate that with heating with steam. Heating with steam will require more energy than 'ordinary' methods of (dry) warming a space since a) you increase the temperature to 100 C instead of the required temperature and b) you need to provide the 'surplus' energy for the transition from water to steam. Some of these losses will be 'regained' by the opposite processes when the steam condenses again, but it's always best to match the produced temperature with the required temperature as much as possible.
    – user2451
    Jan 28, 2016 at 12:28
  • @JanDoggen These are great points. Can you elaborate or comment on user comfort. Would 100 degree dry air allow a user to be as comfortable using 85 degree shower water as 100 degree steam-filled air? Or would there be a difference. And how does that difference translate in terms of energy use?
    – That Idiot
    Jan 28, 2016 at 13:40
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    Who has time to spend 20 minutes in the shower? Is that an average or something from the marketing literature of a luxury shower firm? I suspect the latter.
    – Chris H
    Feb 4, 2016 at 16:54

If you want to save energy, just have a colder shower! It is supposed to be healthier and you can exercise to warm back up. http://www.medicaldaily.com/benefits-cold-showers-7-reasons-why-taking-cool-showers-good-your-health-289524

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    That wasn't the question.
    – That Idiot
    Mar 11, 2016 at 12:24
  • Perhaps not, but it is an answer. Rhetorical question - what is more important to most people, being comfortable or acting ecologically? Mar 11, 2016 at 14:50
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    I actually asked this question in physics, but I thought I'd double down asking here since this group considers energy consumption regularly. As to your rhetorical question - I think the obvious answer is that being comfortable is far more important to far more people than acting ecologically. If it were otherwise the world would be a much nicer place.
    – That Idiot
    Mar 11, 2016 at 15:45
  • Some people like cold showers. I am one of them. I live in the High mountains and my water is well water, pumped by a solar pump and stored in a 7000 gallon tank about 2 feet under ground. Our water line runs about 5 feet underground for about 1500 feet to our house. When it is -18°F outside (-27°C) our water is very cold (some of our lines have even frozen at 5 feet underground). This is when I get the nicest, coldest showers. Some people call me crazy but I just like my showers that way. Mar 16, 2016 at 13:17

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