Electric Shower Installation: Cost, Circuits and the Catch

Fitting an electric shower is not a plumbing job with a bit of wiring attached. It is an electrical job with a bit of plumbing attached. A 10.5kW shower pulls roughly 46 amps, more than an oven and hob combined, and it needs its own circuit running back to the consumer unit in cable sized for the load.

That circuit is where the money goes. The shower unit itself might be £150 to £300. The install can land anywhere from a couple of hundred pounds to well over a thousand, and the difference has almost nothing to do with the shower you picked.

What drives the price

As a rough guide, these are the things that move the number, roughly in order of impact:

• Is there already a shower circuit? Swapping a like-for-like unit onto an existing, correctly sized circuit is the cheap end. An hour or two of work.
• Does the consumer unit have a spare way? If every slot is used, you need a board change or an additional enclosure before anything else happens.
• How far is the bathroom from the board? A first-floor bathroom above the meter cupboard is a short run. A loft conversion at the back of a Victorian terrace is not.
• What is the cable route? Lifting floorboards and chasing walls costs time. A run through an accessible loft void does not.
• Are you going up in power? Moving from 8.5kW to 10.8kW can mean the existing cable is no longer adequate, so the whole circuit gets replaced.
• Making good. Plaster, tiles and decorating are usually separate, and worth agreeing up front.

We will not quote a fixed figure on a page you are reading before we have seen your board. Anyone who does is guessing, and the guess is usually low. What we will do is tell you on the phone which of the above apply to your place, and give you a fixed price once we have looked.

Why the circuit has to be its own

Run the numbers and it becomes obvious. At 230 volts, an 8.5kW shower draws about 37 amps. A 9.5kW draws about 41. A 10.5kW draws about 46. For comparison, a whole ring final circuit serving every socket on your ground floor is protected at 32 amps.

So a shower cannot share. It gets a dedicated radial circuit from the consumer unit, its own protective device sized to the load, and cable sized for that current over that distance. Cable size is a calculation, not a rule of thumb, because it depends on the length of the run, how the cable is installed, whether it is bunched with others and how much voltage drop the circuit can tolerate. Bigger showers in older houses commonly end up on 10mm², smaller ones sometimes on 6mm², but the electrician has to work it out for your run rather than reach for whatever is on the van.

This is also why "can you just spur it off the immersion circuit" is always a no.

The bathroom rules that apply

A bathroom is a special location in the wiring regulations, and the requirements are stricter than the rest of the house.

Everything in or passing through a bathroom needs RCD protection. Electrical Safety First puts it plainly: all circuits in or passing through a location containing a bath or shower must be RCD protected, and if an existing circuit is extended into one, at least the extended part has to be covered.

Isolation matters too. You need a means of switching the shower off that is safe to reach with wet hands, which in practice is a 45A ceiling pull-cord inside the bathroom or a wall switch just outside the door. Not a switch beside the shower at arm's reach.

Then there are the zones. Zone 0 is inside the bath or shower tray, zone 1 is above it to 2.25m, zone 2 extends 0.6m beyond. Each zone has a minimum IP rating for anything installed in it. We break the whole thing down in our guide to bathroom electrical zones and IP ratings, which is worth a read if you are also planning lights or a shaver socket.

Supplementary bonding is the other one that catches people out in older properties. In a modern installation with RCD protection throughout and main bonding in place, it can often be omitted. In a 1970s bathroom with no bonding and a rewireable fuse box, it usually cannot.

Building control, and why it is not optional

Installing a new circuit in a dwelling in England is notifiable work. So is any work in a room containing a bath or shower. That means the job has to be signed off, either by an electrician registered with a competent person scheme who self-certifies it, or by you notifying building control yourself and paying them to inspect it.

The rules sit in Approved Document P. Our fuller explanation of which electrical work needs building regs sign-off covers what is and is not caught.

You should end up with an Electrical Installation Certificate for the new circuit and a building regulations compliance certificate through the post afterwards. Both matter when you sell. If you are unclear which document you have been handed, we have written a guide to which electrical certificate you actually need.

The consumer unit question, asked early

Here is the single most useful thing you can do before booking anyone. Open your consumer unit cover and count the spare ways.

If there are no spare slots, a new shower circuit needs somewhere to live. Sometimes that means a small additional enclosure next to the existing board. More often, if the board is an older split-load unit or a rewireable fuse box, it means replacing the consumer unit, which changes the shape of the job and the price entirely.

The upside is that you end up with RCBO protection throughout and a board that will take the next thing you want to add. Our guide to whether your fuse board is safe walks through what to look for, and the cost of a consumer unit replacement covers that side of it. If it does need doing, that is our consumer unit upgrade service.

Photograph the inside of the board cover and send it over. We can tell you in a couple of minutes whether the shower is a simple job or a bigger one, which saves everyone a wasted visit.

Picking the kW rating

More kilowatts means a warmer shower at a given flow rate, or more flow at a given temperature. It does not mean more pressure, which is a plumbing question about your incoming main.

The practical trade-off is that going bigger may mean a new cable. If your existing shower circuit was sized for 8.5kW and you fit a 10.8kW unit on it, the cable and the protective device may now be undersized for the load. That is not a corner to cut. It is a cable running at more current than it was designed for, buried in a wall, for the next twenty years.

If the existing circuit is staying, match or stay under the rating it was designed for. If you want the bigger unit, budget for the circuit as well.

Questions worth asking before you book

• Will this need a new circuit, or can the existing one take it? If they cannot answer without looking, that is the right answer.
• Who notifies building control? Get it in writing that the price includes certification.
• What cable size and protective device, and why? A good electrician will happily explain the calculation.
• Is making good included? Plaster and tiles, specifically.
• What paperwork do I get? An EIC for a new circuit, minor works if it is a straight swap on an existing one.

Frequently asked questions

Can I install an electric shower myself?

No, not lawfully in England. Installing a new circuit and working in a room containing a bath or shower are both notifiable, so the work has to be certified. Beyond the legal position, a shower circuit is one of the highest-current circuits in a domestic property, run through a wet room. It is not a sensible first electrical project.

Does an electric shower need its own fuse or breaker?

Yes. It needs a dedicated radial circuit with its own protective device at the consumer unit, sized for the shower's load. It cannot share a circuit with sockets, lights or an immersion heater.

How long does an electric shower installation take?

A like-for-like swap on a sound existing circuit is usually a couple of hours. A new circuit from the board, with the cable run to be made and the wall to be chased, is more commonly most of a day. Add time if the consumer unit needs replacing first.

Can I fit a more powerful shower to my existing cable?

Only if the cable and protective device are already rated for the higher load, which has to be checked rather than assumed. Fitting a 10.8kW unit onto a circuit designed for 8.5kW overloads the cable. Have the circuit tested before you buy the unit, not after.

Why does my electric shower need an RCD?

Because it is a high-current appliance in a wet room, where the risk of a fatal shock is far higher than elsewhere in the house. An RCD cuts the supply in milliseconds if current starts flowing to earth, including through a person. In a bathroom it is a requirement, not an upgrade.

Do I need to replace my fuse box to fit an electric shower?

Not always. You need a spare way of adequate rating and a board that provides the required protection. Plenty of modern boards handle it fine. Older rewireable fuse boxes almost never do, and in that case the board change is the honest first step rather than an upsell.

Planning a new shower and want to know what your board can take before you buy anything? See our appliance and shower installation work or call us on 020 3653 2600. Send a photo of your consumer unit and we will tell you straight away whether this is a half-day job or a bigger one.