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Can I replace my 7.2kw shower with an 8.5, 9.5 or 10.8kw model?

Yes, but you will probably require an upgrade in the size of the cable that runs from your fuse-board to the shower as these larger power showers will draw a higher current than your old one.

You will also require an upgrade of the fuse or MCB back at the fuse-board to handle the higher current. 7.2kw showers were typically wired on 4mm or 6mm twin and earth cable and depending on the volt drop calculations that your electrician should run, you will require a 6mm or 10mm cable for an 8.5kw shower and a 10mm cable for your 9.5kw shower.

Your MCB (fuse) or RCBO will also need upgrading to 40,45 or 50A depending on your electrician's calculations.

There is a link to a handy cable size selector on the Fastlec help page that will give you a rough idea of the cable size required for your installation

Do the higher power models, give a hotter and more powerful shower?

They do, but the overall performance of the shower is limited to some extent to your existing cold water pressure - if you have poor mains water pressure then a standard electric shower won't be able to increase that pressure.

Instant electric showers have a powerful element inside that heats the water extremely quickly as it passes through the shower body, so as you can imagine with a very low flow rate, the water takes longer to pass through and therefore comes out of the shower at a higher temperature. Conversely, when you increase the flow rate on your shower, you will usually notice a decrease in temperature as the water passes through more quickly and spends less time in contact with the heating element. With a higher power rated shower such as 9.5kw and 10.8kw, the water is heated much more quickly, so the higher water flow rates don't reduce the water temperature as much (or hardly at all). In general terms you could expect an 8.5kw shower to give you 25% more flow than a 7.2kw shower and a 9.5kw 40% more.

Are electric showers economical? How much do they cost to run?

Even though they use a high power element, they are only running for a short time and usually not at full power so they are surprisingly economical.

As a guideline at current energy prices (14.48p per unit) a 10 minute 8.5kw shower costs around 20p.

How much water do they actually use?

Between 4 to 6 litres per minute depending on your temperature and flow rate settings.

There are lots of different features, what do they mean?

Dual controls - Basic dual controls allow you to leave the temperature set at your favourite setting but you will have to switch the power (flow rate) dial to the required setting each time you shower.

Push-button controls - Showers with push-button controls solely or in addition to rotary controls will usually allow you to leave both your temperature and your flow rate settings in place for your next shower.

Thermostatic control - This allows for fluctuations in water pressure caused by other appliances in the building, by automatically adjusting the temperature to keep it stable.

Phase shutdown - Scale build-up in electric showers is accelerated by the hot water left in the system after you've finished using the shower. Phase shut down flushes the hot water out with cold water at the end of the shower cycle to stop this from happening.

LCD display - Some top-of-the-range showers, show the set shower temperature digitally on the front casing.

Multi-mode shower heads - All but the most basic showers come with a showerhead that can be adjusted to create up to 6 different spray patterns.

Care showers - Showers for the less able come with extended rails, longer hoses, and a host of extra features to protect vulnerable users from potential scalding.

What kind of guarantee can I expect?

Look for a minimum of 2 years. Redring offer 3 and even 5 years with some of their showers. The guarantees usually include (or even insist on) on-site repair, so instead of sending the shower back, an engineer can be booked to fix or replace the shower in your home.