OK

Who doesn't love a nice hot shower in the morning?

But have you considered how much energy your hot shower uses?

As the cost of energy keeps going up and up, I got curious as to how much heat is required for that wonderful morning (or evening) ritual.

The answer surprised me--and it will probably surprise you, too.

The root of the problem is simple thermodynamics. Water is a rather unusual substance--it defies almost every "normal" rule of chemistry. Most of its properties don't track with what you'd expect from such a simple substance. One such property is the heat capacity, or the amount of heat that must be added to a substance to increase its temperature. The heat capacity of water is high for liquids--almost twice as large as any other common liquid.

As a result, heating water to a particular temperature takes twice as much energy as raising the temperature of another liquid by the same amount. So, when you crunch all the numbers, this is the conclusion you reach:

A typical 5-minute shower can power a 25-watt compact fluorescent light bulb for an entire day!

Just to go through the numbers, for any skeptics that read this (or challenge someone who does):

I assume a 5-minute shower, with a 1 gallon per minute flowrate, in a shower with water at 125 degrees F. That's 5 gallons, which is about 19.7 liters of water. I assume the water is piped in at 70 degrees Fahrenheit. That's a temperature change of 55 degrees Fahrenheit, which is about 30 degrees Celsius.

The heat capacity of water is 4.184 Joules per gram per degree Celsius--which means it takes 4.184 joules of energy to heat 1 gram of water by 1 degree Celsius. That doesn't sound like a lot, but just wait.

So, given the assumptions above, one five-minute shower heats 19.7 liters of water (19,700 grams) by 30 degrees Celsius. That's a total of 2,364,000 Joules of energy. To compare this to the light bulb, a 25-watt fluorescent bulb used for an entire day is 25 joules per second times 86,400 seconds per day--for a total of 2,160,000 joules.

Also, remember that water heaters aren't completely efficient--you need to more energy than that to get those results. That means it takes even more than a day's worth of light bulb usage to take that 5-minute shower. And if you like your water a little hotter--say 140 degrees F--that's going to add about another 30% to the total.

When you think about devices in the house that use hot water (like the dishwasher, the washing machine, and the hot tub), you can see how quickly the total energy usage can add up.

I'm not going to be an enviro-scold and say that everybody should only us cold water washes or take cold showers (or worse still, skip showers altogether). However, I was sufficiently astounded by the results that I figured I'd share--and let you make up your own mind about whether or not energy and water conservation can make a difference in your own home.

Originally posted to lone1c on Wed Jul 02, 2008 at 09:59 PM PDT.

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