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AskPablo: Showertime

| Monday December 18th, 2006 | 9 Comments

showering.gif If weren’t a necessary part of good hygiene and if it didn’t feel so good on a cold, groggy morning, the concept of a shower would seem a bit absurd. We take cold water and heat it to around 100°F, then store it in a large tank until we need it. Then it travels through cold and often uninsulated pipes to the far end of the house where it drops down onto our bodies and slips right down the drain. Aside from carrying away dirt, skin cells, soap, and hair it also takes all that heat energy with it down into the sewer… This seems like a model of inefficiency and there must be a better way. Luckily, there are several options. Some can be implemented only in new construction or heavy remodels but some can be done by everyone. I am certainly not going to advocate taking a bucket sponge-bath and donning patchouli oil or waiting for an odor-exorcism when the good Lord returns, so let’s get down to the science and engineering!


The inefficiency begins with the water heater. In a previous AskPablo (Water Heater vs. Stove) we learned that many older water heaters are roughly 67% efficient at converting natural gas into hot water. The inefficiency comes from imperfect heat transfer from the flame to the water, heat losses up the chimney, and heat losses though the walls of the water tank. So a big part of the problem is the storage of water itself. Luckily, there is a solution. Europeans have been enjoying tank-less, on-demand water heaters for over 50 years and they are just starting to become a presence in the US market. These heaters consist of a heat-exchanger and some controls, but no tank. Because of their small size they can also be co-located in the bathroom, eliminating the heat lost to the cold, uninsulated pipes running through your crawlspace or basement. With a tank-less water heater you never run out of hot water, unless you don’t pay your gas bills, and the temperature is always just right.
But assuming that you aren’t planning on remodeling your home anytime soon, there are still ways that you can save money and increase your energy efficiency. Relatively cheap pipe insulation is available at you local hardware store and is very easy to install (if you have easy access to your pipes). You can also purchase a water-heater blanket that will further decrease some of your heat-loss. This may not be necessary on newer models, so consult with your local hardware store professional. If you are planning a major re-model of your home you may want to consider solar water pre-heating. This will increase the temperature of your incoming water (for free), will decrease your natural gas use significantly, and works with both standard water heaters and tank-less models.
The next source of inefficiency comes from the shower head. My shower came with a beastly 15 year-old shower head that blows 3.0 GPM (Gallons per Minute) in your face like a torrential downpour. Let’s say that I enjoy 10 minute showers every day… That amounts to 30 gallons (114 l) per day, or 10,950 gallons (41,450 l) per year! That is not only a huge waste of water, but also of heat energy. One alternative is a 1.2 GPM shower head that was recently featured on Treehugger and is available from Real Goods for $12. Shower heads like this are actually quite powerful and spray droplets rather than just pouring out a stream of water. This particular model also features an easy-to-use switch to turn the water off temporarily while soaping up or shaving.
If I install this shower head I will decrease my annual water use by 6,570 gallons (24,870 l) to 4,380 gallons (16,580 l). But I won’t just be saving water. In the “Water Heater vs. Stove” column I calculated that we need 105kJ of heat energy to heat one liter of water by 25C. Since my water heater is 67% efficient I will actually need 156.7kJ/l (105kJ/0.67). So my annual energy use with the old shower head is 6.5 GJ (41,450 l x 156.7 kJ/l) and my energy savings with the new shower head would be 3.9 GJ (24,870 l x 156.7 kJ/l). These savings are equal to 37 therms (1 therm = 100,000 BTU), or about $42. If I could be convinced to cut my shower time in half as well, the savings would by $84 per year.
I will be covering some other shower efficiency ideas in a future column. But this one is long enough for right now… If you are doing some bathroom remodeling over the holidays, and are eager to get some more ideas feel free to contact me at Pablo(dot)Paster(at)gmail(dot)com.
Pablo Päster, MBA
Sustainability Engineer


▼▼▼      9 Comments     ▼▼▼

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  • http://stonehead.wordpress.com Stonehead

    …where it drops down onto our bodies and slips right down the drain…
    I’ve been thinking about this recently, and was considering fitting some form of heat exchanger to the drain pipes (a coil of copper tubing for example).
    The hot water from the shower or sink would then heat the water in the tubing, which could then be piped into the inlet on the boiler – effectively a preheating system that could work in conjunction with solar.
    Take this further, you could also use with extractor fans in the kitchen – pass the hot air through a heat exchange and use the heat for more water pre-heating (or other purposes).

  • http://www.AskPablo.org Pablo

    Dennis,
    That is a great idea, one which I also had while taking a shower a few months ago (a true shower thought). I looked into this and found that someone had beaten me (and you) to the idea. I can’t find the initial site that I found but here are two pretty good resources: http://www.toolbase.org/Technology-Inventory/Plumbing/drainwater-heat-recovery http://www.smarthome.duke.edu/projects/heat_recovery.php
    Thanks for reading AskPablo!

  • Anonymous

    Pablo,
    Have you tried that twelve dollar shower head?
    It looks like some I’ve used in a few out of the way places that actually hurt.
    I like the button for turning it off while you soap up though.

  • http://www.AskPablo.org Pablo

    I have used this style of shower head in the past. The reason it works with so little water is Because it essentially turns the water stream into a high-speed mist. This ensures complete coverage and therefore makes it feel like more water is being used. The feel of this jet of mist is certainly unique if you are used to the virtual waterfall that you get from some shower heads. I think that it actually feels good and encourages good circulation in your skin tissue. If this is not your thing, there are some other low-flow shower heads that give more of a conventional shower feel, but use a bit more water. If you like the on/off feature you can just get a small valve at your local hardware store that goes between your pipe and your existing shower head.
    Thanks for reading AskPablo!

  • http://uplander.wordpress.com dan19

    As far as that warm water “slipping down the drain”, you could install a greywater bypass to take that used shower and bath water outside to do some good — for example, irrigating your trees, shrubs or flowers. In the dry southwest U.S., bath and sink and washer water is commonly diverted from the sewage stream and used on citrus and other water loving plants. After it passes through the heat exchange, of course…

  • amritt

    Building regulations in the UK now demand the use of heat exchangers on all newly fitted extract vents, no news on the pipe heat exchangers yet but sounds a promising idea.

  • BobW

    I bookmarket this a coupel of months ago:
    http://www.gfxtechnology.com/
    Keep up the good work, Pablo!

  • http://mlliu.blogspot.com Brunswickian

    A friend of mine who attends school in Colombia said that taking cold showers isn’t uncommon there. Heating up water for bathing, especially if one has an electric instead of gas heater, can be expensive. She has friends for whom cost wouldn’t be a concern, but she said they take cold showers anyway because that’s what they’re used to. Funny how something that would seem to be the norm (hot showers) turns out to be just another thing most Americans take for granted.

  • http://www.hotwaterlobster.com Bill W.

    The perfect compliment to a low flow showerhead is The Hot Water Lobster Instant Hot Water Valve! It’s a revolutionary home water conservation product that will save water and get instant hot water to your shower! It saves a lot of water that’s normally wasted down the drain while waiting for hot water. Just install the thermostatically adjustable recirculation valve under the sink farthest form your water heater and you will have instant hot water throughout your entire home. I’ve had one for 3 years now and I’m very impressed!
    The Hot Water Lobster uses no electricity and works off of your existing plumbing! It’s also pump free, so it creates no noise. It’s made in the U.S.A., has a 10-year warranty, and can be easily installed in under 10 to 15 minutes! It even has a money back guarantee! The savings in water and energy quickly recoups it’s low $179.95 purchase price! You can’t beat this product!
    http://www.hotwaterlobster.com