Hot Showers and CO2

showerheadHot showers are one of mankind’s greatest inventions and its a wonder that our fore fathers just a few generations ago were not able to enjoy them on a daily basis as a large part of the globe does these days.

Did you ever consider the annual cumulative consumption of water and energy behind these modern luxuries? More importantly, let also consider the green house gas emissions, especially the CO2 emitted warming the water.


We love hot showers as much (or more) then the next person. This isn’t an indictment on showers, just some thoughts on how to be smarter about optimizing them and get more out of both your soap, water, and the energy used to heat that water. All while still enjoying the benefits of a hot shower.



Katharine Hamnett  -  Ecouterre.com

Katharine Hamnett – Ecouterre.com

From Ask Mr. Electricity

In the big scheme of things the cost of the hot water is really insignificant. Monetarily it’s incredibly cheap, because energy is so cheap (for now) because it does not include the pollution costs of the energy spent by you in heating that water. Keep in mind, that the infrastructure of the water system and shower itself can be expensive (the pipes, tiles, faucets, shower doors or curtains…all add up and can be significant compared to the one-shower energy costs.

Just looking at the shower operation alone and the resources consumed, we have the filtered water, the energy used to heat the water, and the greenhouse gases (CO2) emitted during the heating process. Which by the way, is constant for all water heater types other then the increasingly popular on-demand heater.

How Much Water Whirls Down The Drain Every Year

  • Many people take 300-400 showers a year.
  • Let’s assume 350 showers a year at 25 gallons per shower consuming 8,750 gallons every year
  • That amount weighs 73,000 pounds and would fill a 10x10x10 cube – about the size of a typical bathroom, floor to ceiling.
  • That’s 8,750 gallons of filtered and heat water spraying over you and down the drain.
  • Saving just a part of every shower, let’s assume 20%, equates to 5 gallons every day – saving 1,750 gallons every year

How Much Does This Energy Cost To Heat The Water?

  • A Btu, or British thermal unit, is the amount of energy needed to raise one pound of water from 60°F to 61°F at sea level.
  • A gallon of water weights 8.33 lbs.
  • If the incoming water is 60°F and we want to raise it to 123°F, that’s a 63°F rise.
  • Heating a gallon of water thus requires 8.33 x 63 = 525 Btu’s, at 100% efficiency.

Cost to heat water in a gas tank:

  • A typical gas tank water heater is only 59% efficient. So it takes 525 ÷ 59% = 890 Btu’s to heat a gallon of water in a gas tank.
  • One therm is 100,000 btu’s. So one Btu is 0.00001 therms. (Pacific NW Natl. Lab.)
  • 890 Btu’s is 0.0089 therms.
  • So we’ve got 0.0089 therms to heat a gallon of water, or 0.0089 x 40 = 0.356 therms to heat a 40-gallon tank.
  • At $1.42/therm, it costs 0.356 x $1.42 = $0.51 to heat a 40-gallon tank.

Cost to heat water in an electric tank:

  • A typical electric water heater is 90.4 to 95% efficient. Let’s call that 92.7% on average.
  • So it takes 525 ÷ 92.7% = 566 Btu’s to heat a gallon of water in an electric tank.
  • One kWh is 3413 Btu’s, so one Btu is 0.000293 kWh.
  • 566 Btu’s x 0.000293 kWh/Btu = 0.166 kWh.
  • So we’ve got 0.166 kWh to heat a gallon of water, or 0.166 x 40 = 6.63 kWh to heat a 40-gallon tank.
  • At $0.11/kWh, it costs 6.63 x $0.11 = $0.73 to heat a 40-gallon tank.”

How Much (CO2) Is Emitted

  • If the incoming water is 60°F and we want to raise it to 123°F, that’s a 63°F rise.
  • Heating a gallon of water thus requires 8.33 x 63 = 525 Btu’s, at 100% efficiency.
  • Heating a 8,750 gallons requires 8,750 x 8.33 x 63 = 4,593,750 Btu’s, at 100% efficiency.
  • At a blend of 50/50 gas/electric (59% and 93% efficiencies) or a combined 76% efficiency thats 4,593,750 ÷ 0.76 – 6,044,408 Btu’s.
  • At a blend of 50/50 (coal/propane) (140/200) pounds of CO2 per million BTu’s, or 170 pounds.
  • 170 pounds of CO2 x 4.6 million BTu’s emits 784 pounds of CO2.
  • One pound of CO2 occupies 8.56 ft3 or 6,713 cubic feed of CO2.
  • Approximately the volume 2.5 tractor trailers of CO2 for just your showers every year.
  • Extended across an 80 lifespan, that 200 tractor trailers of CO2just for your showers
  • And there are billions of other shower-takers in the world!





How To Save 5-10 Gallons Every Day Shower the Navy Way This method of showering was developed by the navy as a means of saving water while at sea. Its simple: Quickly get completely wet, turn off the water, lather up with soap, shampoo, shaving cream, etc., let these cleaning agents do their job, and after a few minutes of soaking in the soap suds, and turn the water back on and rinse. Seems logical, right? Rather than have the freshly applied soaps get quickly washed off, let the soap soak in for a minute and then rinse clean.

Keith BlizzardShowering this way can use as little as 10 gallons of water every shower. PLUS, it gives the soap and conditioner a chance to activate and thoroughly do its job.  Makes a ton of sense instead of immediately washing it off and down the drain, only to apply more suds to get the job done.


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About the author

Keith Blizzard

A life-long environmentalist, Keith set out on the never ending journey of adjusting his lifestyle to a more sustainable one, with a goal of annually shrinking his carbon footprint. When he looked around for a dependable source of meaningful carbon footprint reduction ideas, it was pretty lame - so he launched Green Blizzard loaded with eco-friendly lifestyle tweaks. When he's not managing Green Blizzard, you'll find him on the trails around Mid Coast Maine with his trusty trail companion mutt, Moose.