site updated 30 August 2019 2009-2019

lovekin power shower guide

Link to Lovekin Power Shower Guide home page

We're developing this Web site to provide a review of the types of shower available for domestic properties. We'll be looking at:

We'll also take a look at shower heads and riser rails, thermostatic mixing valves, shower enclosures, trays and wet rooms.

But before you start, please read our legal disclaimer

A guide to the different types of showers available:

gravity showers, electric showers and power showers

Legal disclaimer:

The information provided in these pages is given in good faith and is only designed to provide an overview of the subject. We can accept no liability for any damage or injury sustained in connection with the installation or use of any shower system, nor any liability arising out of misleading, incomplete or incorrect information on this site.

Gravity Showers

We've decided to include gravity showers partly to provide a benchmark against which to compare power showers and partly because they have significant plus points.

Taking the obvious negative point first, gravity showers generally lack power, providing low flow rates and a weak spray but this isn't always the case.  If a gravity shower is sited on the ground floor of a house and the cold tank which supplies water for the shower is in the loft, good flow rates can be achieved, particularly if the right shower head, mixing valve and pipe sizes are used.

In hard water areas lime scale is a problem but that applies to power showers too and we'll look at lime scale later.

Drawing showing how gravity showers operate from a hot water cylinder and loft cold water tank.

How Gravity Showers Work

When the shower mixing valve is opened cold water falls from the cold water storage tank in the loft, passing through the mixing valve and out of the shower head.

At the same time cold water falls from the loft tank into the bottom of the hot water cylinder. It pushes hot water stored there up and out, into the mixing valve and out of the shower head.

By adjusting the mixing valve you control the temperature and the flow rate or the water coming out of the shower head.

Gravity Shower Plus Points

The flow rate of a gravity shower depends on a number of factors. The bigger the distance vertically between the shower head and the level of water in the cold tank, the faster the shower will flow. Extra height adds far more than the extra resistance in the pipes  but horizontal pipe runs just add resistance and should be kept as short as possible. In flats where the cold tank can't be sited in a loft, gravity showers give very poor flow rates and in flats where Fortic™ type cylinders are used (these have a small cold tank built directly onto the top of the hot water cylinder) gravity showers are almost useless.

Gravity Shower Flow Rate Factors

Flow rate also depends on pipe sizing, the bigger the pipes the better. Different pipe materials can be significant; some of the newer plastic pipes are very smooth bored and have low resistance to water flow. They can also be "cabled" through in continuous lengths with very few joints. All pipe joints add significant resistance and for best results with copper pipes the pipes should be fully de-burred.

The type of mixer valve and shower head is also important. Some manufacturers make equipment with low flow resistance specifically designed for gravity showers. If the spray head can be hand held you should ensure that the hose connected to the head has the largest bore possible. The bore of shower hoses varies enormously, with some having a bore whose cross-sectional area is 4 or more times larger than others.

Bath/shower mixer taps are not ideal as the bore through them is generally very small so the resistance is high. Some bath/shower mixer taps now suggest a minimum pressure needed to operate the shower adequately. If the box says the mixer needs 1 bar head of pressure you need a water tank about 33 feet (10 metres) above the shower head. With significantly less water pressure, flow rates may not be the only problem; the diverter valve in mixer taps is often held in the shower position by water pressure and with low pressure it may refuse to stay in position.

Electric Showers

More on Flow Rates - Gravity Showers

To get a good gravity shower everything must be done to maximise flow. A high flow shower head should be used. It may be possible to enlarge the holes in the head.

Thermostatic mixer valves limit temperature fluctuations but they may significantly reduce flow. This poses problems for gravity showers and it's worth considering a manual (non-thermostatic) mixer valve.

The risk is that someone draws off cold water while you're using the shower (e.g. flushes a loo) and cold to the shower is reduced, scalding you. One way round this is to run an independent cold pipe directly from the cold tank so you get little or no pressure fluctuation on the cold; if someone uses the hot water you may be chilled but not scalded.

Independent hot pipework can be run to prevent this but the hot flow rate also depends on the size of the cold pipe from the cold tank to the bottom of the hot water cylinder. If a large bore pipe is used here, and an independent hot pipe from cylinder to shower, temperature variations can be minimised.

Finally, if flow matters more than looks, use two full-bore lever valves in place of a mixing valve, one on the hot and one on the cold. Tee them together and use a fixed shower head with enlarged holes. It may not be pretty but it will be quiet, reliable, have good flow rates and be much less susceptible to lime scale problems.     Back to the Top

Electric showers use mains pressure cold water and don't need a stored hot water supply. The heating unit is contained within a small packaged shower unit attached to the wall. The heating element is several times more powerful than an electric kettle, allowing the water to be heated from cold as it passes over the element.

None of the electric showers currently available can produce flow rates comparable to the other power showers but they can be cheap to install.

Electric Shower Electrical Requirements

A heavy duty electrical cable is required and if an existing electric shower is replaced with a higher powered one (for instance a 10kW shower replacing an 8kW shower) a larger cable may be required. The size of the cable needed also depends on cable length and where the cable is run; it should not be run in, or under, loft insulation. Specific isolation switches are required and the circuit should be fitted with a trip which senses any leakage of electrical current to earth, either an RCD or an RCBO. The electrical rules are strict and crucial to your safety.  You will need to consult an electrician who is qualified under Part P of the Building Regulations.

Electric Shower Flow Rates

With electric showers, flow rate is almost always limited by the rate at which the water can be heated. Some have a low setting which is hardly ever used (not many of us are looking for cool or cold showers). The setting is left on high and the temperature is controlled by reducing or increasing the amount of water passing through. The shower can only heat at a set rate and the amount of hot water reduces in Winter. This is because the incoming mains cold water is much colder in Winter; it needs more heat to reach the same temperature so you slow the flow rate down to keep it in contact with the heating element for longer.

Electric Shower Running Costs

As a form of energy electricity tends to be more expensive than gas (at least in the UK). Even with gas prices increasing, electricity is generally more than twice the price of gas. This would appear to make electric showers much more expensive to run but the lower flow rate evens things out. Pumped power showers, usually heated by gas, pass much more water. The flow rate of a pumped shower may be 2 or 3 times higher giving much better showers but may be no cheaper to run if they're used on full.

And the benefits of electric showers? They are often cheaper to install and, not having a pump, they can be much quieter than a pumped shower. If you don't have an alternative choice of energy they're the only choice anyway. Finally, if you love cold showers you can get brilliant flow rates for almost no cost!     Back to the Top

Power Showers From a Combination Boiler or Multipoint Water Heater

Combination boilers (often called combi boilers or combies) provide hot tap water on demand. They heat the central heating water in much the same way as regular boilers but when a hot tap is opened they switch over to providing hot tap water. With combi boilers there is generally no hot water cylinder. Some larger combination boilers store a limited amount of hot water within the boiler provide a "head-start".

Multipoint water heaters are similar to combination boilers in that they also provide instantaneous hot water. They don't, however, provide heating for the house.

Combination Boiler Shower Flow Rates

Most combination boilers now fall in the range of 25kW output to 39kW output. They can heat tap water 3-4 times faster than electric showers and much higher flow rates can be achieved, giving much more powerful showers.

Because showers run from combi boilers can have much higher flow rates, running costs can be higher than electric showers even though gas (in the UK) is much cheaper than daytime electricity. Showers run from multipoint water heaters usually cost less than electrically heated showers and the flow rates are much better, though not as good a combi boilers.

Higher flow rate showers are, however, much more pleasurable and as the water is constantly being heated it never runs out. This can lead to much longer shower times and can be more expensive than running a bath. With gas prices (January 2017) about 5p for each kWhr, showers from combi boilers cost about 1.50 per hour, just to heat the water. A family taking between them three 10 minute showers per day will spend about 270 per year. Some people are much more frugal. If you can restrict your shower time to only 5 minutes (5 minutes with the water running) you could save half of that.    Back to the Top

Combination Boiler Shower Running Costs

Venturi Power Shower

In nearly all geographical areas in the UK mains water is at much higher pressure than low pressure water supplied from a loft tank in a house. In most areas mains pressure is around 2-3 bar though it may be much higher. Three bar is enough to push water to the top of a pipe 30 metres high (100 feet). The stored energy which generates this pressure is called potential energy.

Venturi power showers use the potential energy in mains cold water in a simple and really clever way  to draw in low pressure hot water and mix it with the mains cold water. No pump is used to deliver the water to the shower head.

Venturi power showers do not heat the water. They are clever because they can deliver a high flow shower using low pressure hot water stored in a standard hot water cylinder.

Venturi Power Shower Flow Rates

It's very hard to find published flow rate figures for venturi power showers, mainly because their flow rates depend on so many variables. Hot water may need to be stored at 65C and mains cold pressure must be adequate (but not excessive); then it seems that flow rates will vary from 10 litres per minute to maybe 20 litres per minute, depending on the installation. A major factor will be the flow rates of hot water from the storage cylinder. Low resistance check valves should be used (swing check valves if possible) and larger pipes with fewer tight bends. Then, the higher the cold tank (which feeds the hot water cylinder) is above the shower head, the better.

Pumped Power Shower

Packaged pumped power showers

Separate power shower pumps

Single impeller shower pumps (can be fitted to pump either hot water or cold water or blended water)

Twin impeller shower pumps (one impeller pumps hot water, one pumps cold but both impellers operate at the same time)

Flow switches

Positive head shower pumps

Negative head shower pumps (shower pumps which can be fitted where the pump is located at or above the level of the shower head)

Venturi Shower Running Costs

With all showers, the main running cost involved is the cost of heating the water so the higher the flow rates, the more you pay. Venturi power showers can achieve high flow rates under optimum conditions and, when they do, the running costs will be higher. Remember, it depends on what fuel you use to heat the water in the first place. Daytime electric rates are high!    Back to the Top

Pumped Power Shower Flow Rates

Pumped power shower flow rates vary widely. The type of shower head and shower hose make some difference but the big difference is in the power of the pump. These range from small, relatively cheap pumps bought from DIY outlets, to powerful pumps from specialist manufacturers.

Really powerful shower pumps are capable of emptying the loft tank of cold water faster than it can fill, so beware!

Pumped Power Shower Running Costs

The running costs of pumped power showers varies with the power of the pump and the amount of water it can deliver through the shower head. The faster the flow rates, the more expensive to run. The other variable is the cost of the fuel used to heat the water for the power shower.    Back to the Top

Power Showers from Unvented Hot Water Cylinders

Megaflo™ hot water cylinders

Minimum 22mm equivalent incoming cold water main is recommended

Power Shower Flow Rates from Unvented Cylinders

A power shower run from an unvented hot water cylinder can produce phenomenal flow rates many times higher than electric showers or most gravity showers. The high flow rates make it possible to run several jets at the same time (shower head and body jets), depending on the shower equipment used.

Power Shower Running Costs from Unvented Cylinders

Power showers run from unvented hot water cylinders are capable of delivering so much water that they rapidly become more expensive to run than using a bath. In the UK, gas prices are currently about one third of daytime electricity prices but unvented hot water cylinders are rarely heated by electricity. Even so, a power shower run from an unvented hot water cylinder can be very expensive to run if you use its full potential. If you have an all-singing, all-dancing power shower delivering about 30 litres per minute, you may be tempted to stay in it for longer. A 10 minute shower will cost you about 60p. One shower a day (January 2017 gas prices) will cost you 220 each year!    Back to the Top

Power Shower from Thermal Store Cylinders

Albion Mainsflow™ hot water cylinders and thermal stores

Power Shower Flow Rates from Thermal Store Cylinders

Like showers from unvented hot water cylinders, a power shower run from a thermal store cylinder is capable of giving amazing flow rates and capable of running body jets as well as the shower head.

Power Shower Running Costs from Thermal Store Cylinders

Power showers run from thermal stores or from unvented hot water cylinders, showers run from combi boilers and pumped power showers all have similar running costs for similar flow rates (assuming the same fuel is used to heat the water). The faster the shower flow rate, the more it costs per minute to run.

All power showers can be expensive to run but a power shower run from a thermal store cylinders can deliver hot water so fast that it is easy to make showering more expensive than running a bath.

Environmentally too, the cost of running very high flow rate showers may become unacceptable over the next few years.

Back to the Top

Unvented Hot Water Storage Safety Regulations

Stringent safety regulations apply to pressurized hot water storage of over 15 litres. These storage cylinders and their controls must not be modified in any way not specified by the manufacturers. See Approved Document G, G3

Gravity Showers

Electrically Heated Showers

Combi Power Showers

Venturi Power Showers

Unvented Power Showers

Thermal Store Showers

Multipoint water heaters are less powerful with an output of up to 24kW so the flow rates you can achieve are lower but they are still 2-3 times better than electric showers.

With showers run from combination boilers or multipoint water heaters however, temperature fluctuations can occur if hot water is drawn off from another point served by the appliance. This effect is limited by fitting a thermostatic shower mixing valve and this is recommended.

Combination Boiler Shower Problems

We recently came across a problem using an Aqualisa Quartz digital shower with an older combi boiler. Most newer combination boilers modulate the flame as the water flow rate through the boiler is slowed down or speeded up. Some older combi boilers do not have modulating gas valves, they simply shut the burner down when the flow rate decreases more than a certain amount (or the water temperature rises) and fire up again when the flow rate increases (or the water temperature reduces). This may make them incompatible with shower units which modulate the amount of hot water being drawn from the boiler.

Before fitting an Aqualisa digital shower (or any similar digital shower) to a hot water system using a combi boiler, talk to your installer or to Aqualisa technical. They should be able to tell you what will or won’t work.    Back to the Top