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Electric showers

by Chris Woodford. Last updated: November 7, 2013.

Are you a shower person or a bath person? Do you like to feel pulsing jets of water blasting your dirty skin clean? Or do you prefer to laze luxuriously in the tub until the water turns cold? If you wash for less than five minutes and your shower has a modern, low-flow head, you'll save over 50 gallons of water and a huge amount of energy compared to taking a full bath. Saving hot water with a shower helps to cut your energy bills and it's a simple thing you can do to fight global warming. Sounds good? Let's take a closer look at how showers work!

Photo: A simple Mira electric shower. There are two controls for adjusting the temperature. The upper dial sets the temperature broadly as high, medium, or low. Once you've set the temperature roughly, the lower dial lets you fine tune to get the water exactly as hot as you want it.

How do mixer showers work?

The simplest showers are called mixer showers and, as their name suggests, they work by mixing hot and cold water from separate pipes to make warm water whose temperature is somewhere in between. The most basic form of mixer shower is a Y-shaped rubber pipe that you fit over the hot and water faucets (taps) on a bath-tub. By adjusting the faucets, you create a single stream of water at exactly the temperature you want.

The trouble with mixer showers like this is that the temperature is hard to control. If someone switches on a cold faucet or flushes a toilet elsewhere in your home, the cold water supply is suddenly reduced. That means there's proportionally more hot water coming through your shower and, if the water's too hot, you could be scalded. The opposite will happen if someone switches on a hot faucet—you'll suddenly find the shower turning freezing cold!

A thermostatically controlled mixer shower unit showing the hot and cold pipes and the hand control

Mixer showers that are plumbed into the wall overcome this problem by using built-in thermostats. They constantly adjust the temperature of the mixed water to ensure you're not boiled like a lobster or frozen like a penguin by water that's alternately too hot or too cold. Most mixer showers also have safety cut-outs that prevent you from turning the water up to dangerously high levels, which is good news if they're being used by frail elderly people or young children.

But there's still a basic problem with mixer showers: they typically run off hot water from a tank. Once the tank is empty, there's no more hot water and you have to wait for the tank to fill up before you can shower again.

Photo: A typical, thermostatically controlled mixer shower. Hot water and cold water flow in through the two pipes in the wall (top), mix in the valve unit in the center, and flow out through the curly hose at the base, which connects to the shower head. This is a really simple shower: you simply turn the knob to switch the water on cold, then keep turning it clockwise to make the water as hot as you wish.

How does an electric shower work?

Electric showers overcome this problem by heating cold water with electricity. They never run out of hot water, so they're a great solution if you have lots of people in your house who like to shower one after another.

Electric showers work in much the same way as other electric appliances that get hot, including electric toasters and hair dryers. They send an electric current through a piece of metal called a heating element. This has a moderately high resistance, so it gets really hot when electricity moves through it. Cold water flows past the element, picking up heat and heading out through the nozzle where you're standing.

You probably know that water and electricity are usually a very dangerous combination, but electric showers are perfectly safe if they're properly fitted. That's because a heating element is a completely sealed unit. The electric current flows through the element, but not in such a way that it can give you a shock. No electricity comes into contact with the water that touches you.

You can adjust the temperature of an electric shower by turning a dial, which is usually marked with a scale running from blue (for cold) to red (for hot). This controls a thermostat that cycles the heating element on (to make the water hotter) and off (to cool the water down) so it always remains at exactly the temperature you set.

How do power showers work?

For an electric shower to work effectively, you need a cold water supply with reasonably high water pressure to begin with, because the shower heating unit will reduce the pressure of the water as it flows through. If you don't have enough water pressure for an ordinary electric shower, the solution is to fit a power shower. It takes in and heats cold water just like an ordinary electric shower, but it also uses an electric pump to increase the water pressure so it leaves the nozzle with greater force and higher speed. If saving water and energy is important, bear in mind that power showers use 3-5 times more than ordinary showers. That means a lengthy power shower can easily cost you as much as a generous bath-tub full of hot water!

How an electric power shower works: in a nutshell

Diagram showing how an electric shower works

  1. Cold water flows in from the cold pipe.
  2. Electrical energy flows into the heating element.
  3. The heating element heats the cold water.
  4. The thermostat constantly measures the temperature of the heated water.
  5. If the heated water is too cold, the thermostat turns the heating element on; if the water is too hot, it turns the heating element off.
  6. The pump increases the flow of hot water.
  7. Hot water flows out through the outlet hose toward the nozzle.
  8. Holes in the nozzle turn the rush of hot water into a diffuse, efficient spray.

Do showers save energy compared to baths?

Which costs more, a shower or a bath? Generally, showers use less energy because they use less water, but it all depends on your shower and your bath. If you have a modern electric shower with a low-flow head and you use it for only three or four minutes, it'll be very efficient and should save you money compared to taking a bath. If you have a power shower and you stand under it for 15 minutes, don't expect to save much—you may even find it costs you more! If you have a shower over your bath-tub, the simple way to test whether you're saving anything is to take a shower with the plug in place. Broadly speaking, if you use less water, you're saving energy and money; the less hot water you use, the more you save. (Of course, the calculation changes somewhat if your shower is using hotter water than your bath—or vice-versa.)

If you have a separate bath-tub and shower cubicle, comparing costs is more tricky. If you know your math, you could read your electricity (or gas) meters before and after taking a bath and shower and calculate the cost using the difference in the readings. Or you could use an electrical energy monitor, though that won't help you if either your bath or shower is powered by gas or oil!

Are eco-friendly shower heads worth buying?

One of the most basic (and useful) laws of physics, the conservation of energy, tells us that we can't create or destroy energy: we can't pluck it out of thin air or make it vanish completely, only convert it from one form into another. If you want to reduce the amount of energy you use in the shower (or the money you spend), the conservation of energy tells us that the only ways you can do so are:

The conservation of energy says electric showers cannot save energy and provide the same quality of wash.

So what about eco-friendly, replacement shower heads that claim to save water and money? Again, the conservation of energy tells us that any gains you make have to be lost somewhere else. If your shower is saving energy, it can do that only by reducing the amount of water you're using or the temperature of the water. It can't give you exactly the same quality of shower (equally as hot for just as long using exactly the same amount of water) if it's simultaneously saving energy; the laws of physics simply don't allow that! Eco shower heads typically work by reducing the amount of water flowing through them. Since they tend to be quite expensive, they may not actually be saving you any money at all—and you can achieve exactly the same effect by either turning down the water at the faucet (mixer showers usually let you do that, but electric showers often don't), showering at a slightly lower temperature, or showering for less time.

Photo: Electric showers use heating elements that are almost 100 percent efficient so, broadly speaking, the heat energy you get out is the same as the electrical energy you put in. What that means is that if you want to save on the energy you put in (to help the environment or save money), you must also save on the energy coming out either by reducing the temperature, water flow, or the time you spend in the shower.

How do pulsating shower heads work?

A simplified diagram showing the turbine and rotor mechanism inside a pulsating shower head.

Power showers are great for tired bones, but pulsating showers can be even better if you want to massage your aching muscles at the same time. How do they work? Although there are various different designs, most rely on the pressure of the water jet to turn a miniature water turbine attached to a rotating wheel inside the shower head. The wheel has one or more holes in it so it interrupts the water flow intermittently, giving regular blasts of pressurized water through the shower head nozzles instead of a constant stream. It's a little bit like a garden sprinkler, where a cam driven by the pressure of the incoming water trips the outgoing flow on and off.

Photo: In a pulsating shower head, the pressure of the incoming water (1) powers a small turbine (2) that makes a wheel rotate (3). Holes in the wheel interrupt the incoming water flow periodically giving hammering pulses of outgoing water (4). This is a very simplified version of what's going on; for a much more detailed description and diagrams, see the patent documents listed below.

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Patents

You'll find very detailed, illustrated descriptions of two pulsating shower head designs in these patent applications:

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Text copyright © Chris Woodford 2008, 2012. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2008) Electric showers. Retrieved from http://www.explainthatstuff.com/electricshowers.html. [Accessed (Insert date here)]

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