Showers - the types available

Showers...

This rather long (and hurriedly written) page gives you the basic types of shower, how they work, and their characteristics. (You might like to print it and read it off-line.)

Absolute basics…

There are two fundamental types of shower…

Showers which heat the water themselves (electric showers)
Showers which get their hot water from the household hot water system (mixer showers)

Now more detail…

Electric Showers…

Well known examples of the electric shower are the Triton T80 and the Dolphin Electric Shower.

Water is heated by an electric element as it passes through the shower unit. Most electric showers are fed directly from the mains. In some geographical areas mains water pressure is variable or unreliable, particularly at peak times (early morning and evening). This can affect electric showers. When mains water pressure falls below a particular value (set by the maker) the shower will automatically turn off until pressure rises again. To prevent this infuriating effect, some electric showers are connected to the cold water storage tank and have a pump inside to deliver constant pressure. (This pump does not increase the flow rate, just the reliability.)

Characteristics of the electric shower:

The shower works when the hot water tank is cold. This suits the way some people use their water heating systems.
The shower never runs out of hot water. The whole family can have consecutive showers without fear of the shower running cold.
Only the water being used is heated, giving economy. No water is heated unnecessarily.
Shower can be fitted anywhere a mains cold pipe can reach. Installation in loft conversions or areas without a stored hot water service can have an electric shower.
Low flow rate. The shower flow is controlled by the power of the heater element and the temperature selected by the user. The highest power electric showers do not achieve the flow rates offered by mixer showers
Water scaling. Electric heater elements scale up with use. You will need to replace the shower unit from time to time, or fit a water softener. The Mira 'Advance' electric shower addresses this problem by making the heater element simple to remove for descaling or replacement. This saves replacing the whole shower if it becomes scaled. However, the Mira 'Advance' costs much more than a basic electric shower.
Dependence on water company supply pressure. I know from experience that mains water pressure is too low at peak times to operate an electric shower in certain areas of Berkshire. This can be overcome by connecting the shower to a cold water storage tank with a pump to boost the pressure (at enormous expense!) or selecting a shower with a built-in pump.
Unstable temperature. Despite the claims of manufacturers, in my experience electric showers can be sensitive to other taps being operated while the shower is in use. The Mira 'Advance' electric shower overcomes this problem by having thermostatic temperature control.

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Mixer Showers…

Bath/Shower Mixers…

The simplest mixer shower is the 'bath/shower mixer'. This is the bath mixer tap with a shower hose connection built into it. Almost all tap ranges include a bath/shower mixer and they will be familiar to everyone.

They are the least expensive and least sophisticated option, and are mainly responsible for the poor reputation of UK showers. When they are connected to high pressure cold water and low pressure hot water supplies (common in UK bathrooms) they barely work at all. The shower temperature is difficult to adjust, when you get it right it changes slowly, and if other taps are operated the temperature swings wildly. The high pressure (mains) cold water supply is the culprit here. When a bath/shower mixer is connected to balanced supplies (low pressure cold, low pressure hot) they work reasonably well, with limitations. In particular, the temperature becomes easier to set, but you need to consider the following points:

It is essential to connect a bath shower mixer to hot and cold water supplies which are approximately equal in pressure. When these equal supplies are from a cold water storage tank, the shower flow will be quite feeble because the pressure is low. The flow also reduces as the shower head is raised to normal showering height.
Most bath/shower mixers have conventional rubber tap washers. These cause the temperature to drift over the length of a shower, demanding constant re-adjustment. This effect is absent if you choose a bath/shower mixer with modern ceramic-disc cartridges.
The shower water temperature can be affected when another tap or water fitting is operated. The more people in a household, the more often this effect will be experienced!
Adding a booster pump will improve the performance of a bath/shower mixer, but this rather defeats the point of choosing one in the first place (low cost).

In summary, my view is that a bath/shower mixer is best chosen for hair-washing and cleaning the bath. If you want a proper, stand-up shower, you could find it disappointing.

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Separate Shower Mixers:

With a separate shower mixer on the wall you can have these desirable features…

Stable shower temperature: Other people can flush WCs, run taps, start the washing machine and the shower user won't notice!!! This is done by fitting separate feed pipes to it from your hot and cold water tanks.
Higher flow rates: Modern shower mixers are built with large internal waterways to make best use of the available pressure. And you can add a pump to reliably boost the pressure further.
Simple controls: Usually two control knobs. One control turns the shower on and off, the other adjusts the temperature. Some mixers (for example, the Ideal Standard Trevi Blend) have single lever control. You lift the lever to turn on, and move it from side to side to adjust the temperature.

A mixer on or built into the wall also forms the basis of a 'power shower'. See next section…

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Thermostatic Showers…

These have a temperature sensing device which adjusts the hot/cold mix. The user selects the temperature required and the thermostat does the mixing. This method of control delivers several benefits as follows:

Stable shower temperature. If a hot or cold tap is operated elsewhere, the water pressure may change causing the water temperature from a non-thermostatic shower to change. A thermostatic shower detects this change and adjusts the hot/cold mix automatically to compensate, maintaining a stable water temperature for the shower user.
No shower temperature drift. As a user takes a shower, the stored hot water temperature will reduce, causing the shower water temperature from a non-thermostatic shower to gadually reduce. A thermostatic shower detects this change and adjusts to compensate, maintaining a constant water temperature for the user over the length of his shower.
Safety: If the cold water supply to the shower should fail, an ordinary mixer will deliver hot water only. (A safety risk particularly to children and elderly users.) The action of a thermostatic shower trying to compensate for the rising shower water temperature is to cut down the hot water flow. When the cold supply has failed, the hot will be reduced to a trickle, effectively turning off the shower under fault conditions. Most thermostatic showers also have temperature limiting devices built in to prevent very high temperatures being mistakenly selected by the user.

However, thermostatic showers also have the following drawbacks…

Thermostatic showers need hotter stored water water than manual mixer showers. Typically, 60 degrees Celsius is the minimum hot water temperature required by thermostatic mixer showers. I often find households with young children have their hot water set to around 50 degrees Celsius, to minimise the chances of the children accidentally scalding themselves under the water from a hot tap.
Expense. Thermostatic showers designed for UK plumbing systems are around twice the price of equivalent manual shower mixers.

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Power Showers…

The term 'power shower' is a loose expression for any shower system which includes a method of boosting water flow. Generally, this means a shower mixer with a booster pump but it can also mean a shower connected to a mains pressure hot water system or a venturi type shower.

Pumped Showers:

A pumped shower needs to have hot and cold feeds from storage tanks. You cannot successfully use a pump to make a power shower from an electric shower or any other shower connected directly to the mains cold water supply.

There are two methods of pumping shower water. Single impeller pumps and twin impeller pumps. Early pumped showers had an electric motor driving a single pump impeller connected between the shower mixer outlet and the shower head. This method has fallen into disuse because of pump location limitations. The most convenient pump location is in the loft above the shower, but this leaves the pump prone to frost damage (it can't be insulated because of the ventilation requirements of the motor) and often transmits pump noise around the upstairs of the house. Other locations mean awkward pipe runs and longer pipe runs between mixer and shower head, which delays response of the shower to temperature control changes by the user. Current systems generally use a motor driving two separate impellers pumping the hot and cold supplies before the shower mixer. This means the pump can be located anywhere in the pipe route from tanks to mixer. The most common convenient location is in the airing cupboard.

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Shower Heads:

'Power shower' also implies a shower head with a choice of functions. Most power shower handsets have a conventional spray setting, and a champagne setting (with lower flow and lots of air mixed in, giving a bubbly effect), and a massage setting, where a concentrated and powerful spray pattern pulsates around ten times a second. Powerful systems can also have 'body jets'. These are sets of shower heads pointing sideways and mounted in a vertical line on one or two walls of a shower enclosure. There needs to be an additional control inside the shower enclosure - a divertor valve to switch water from body jets to overhead handset, or both together.

All-in-One Power Showers:

This is the current trend in power showers. A shower mixer and pump are built into a case which looks rather like an electric shower, but delivers true power shower performance at much lower cost than the remote pump systems described above.

Venturi Showers:

These work on the same principle as a carburettor on a car. Cold water passing through a restriction tube (venturi) causes hot water to be drawn in and be mixed with the cold water. By controlling the amount of hot water introduced, the shower mixer controls the shower water temperature. Venturi showers give a higher water flow than an electric shower and can be used when the stored hot water pressure is too low to work a gravity-fed mixer shower or conventional power shower.

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Showers when you have a 'combi' boiler:

Combi boilers (and multipoint water heaters) are gas boilers which draw domestic hot water directly from the cold mains supply and heat it as you use it. This avoids the need for hot or cold storage tanks, but creates headaches where showers are concerned. If shower performance is poor, it is usually because mains water pressure is poor, and there are no remedies apart from installing a different boiler and hot water system. With combis, you are dependent on the pressure and consistency of the mains water supply. In hot weather mains water can fall to very low pressures at peak times, meaning combi boilers and showers may not work.

Some manufacturers recommend using their standard thermostatic shower model with combi boilers, but performance cannot be guaranteed. The thermostat in a thermostatic shower can contradict the action of the boiler thermostat, though this is unusual.

The type of shower designed specifically to work with a combi boiler is called a 'pressure balanced' mixer shower. The best example is the Mira 415.

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