July 8, 2026 Jonathan Murphy

Electric or Thermostatic Shower? How to Choose

Choosing a new shower sounds simple until you start looking. Two types dominate the Irish market - electric showers and thermostatic showers - and they work in fundamentally different ways. One heats water itself; the other blends water your boiler or cylinder has already heated. Which is right for you depends far less on personal preference than most people expect, and far more on the plumbing you already have behind the wall.

In this guide we'll explain how each type works, what separates them in day-to-day use and how to work out which one suits your home before you spend a cent.

How an Electric Shower Works

An electric shower takes cold water directly from your mains supply and heats it on demand using an internal heating element - much like a kettle, but continuously as the water passes through. It has no connection to your hot water cylinder, immersion or boiler at all.

Because of this independence, an electric shower will give you hot water whenever you want it, even if the immersion hasn't been on and the boiler is off for the summer. That makes it genuinely useful in a second bathroom, an ensuite, a converted attic or any household where hot water runs out before everyone has washed.

Electric showers are rated in kilowatts, typically from around 8.5kW up to 10.8kW. The rating tells you how quickly the unit can heat water, which in turn determines flow rate - a higher kW model pushes out more water at the same temperature. It's worth knowing that performance shifts with the seasons: incoming mains water is colder in winter, so the same unit delivers slightly less flow to reach your chosen temperature.

How a Thermostatic Shower Works

A thermostatic shower is a type of mixer shower. It draws both hot and cold water and blends them to the temperature you set, using a thermostatic cartridge inside the valve. That cartridge contains an element that expands and contracts as water temperature changes, continuously adjusting the hot-to-cold ratio to hold your setting steady.

The practical benefit is immediate: when someone runs a kitchen tap or flushes a toilet elsewhere in the house, the shower compensates instantly instead of turning scalding or freezing. Thermostatic valves are also designed to fail safe - if the cold supply is lost, the valve shuts the flow off rather than delivering unmixed hot water.

This is the key distinction from a basic manual mixer shower, which blends hot and cold in a fixed ratio and offers no such protection. If you're comparing options, check specifically for the word "thermostatic" rather than assuming any mixer includes it.

The Key Differences at a Glance

Water source: Electric showers use cold mains only. Thermostatic showers need both a hot and a cold supply.
Independence: An electric shower works regardless of your boiler or cylinder. A thermostatic shower depends entirely on stored or on-demand hot water being available.
Flow rate: Thermostatic showers generally deliver noticeably stronger flow, particularly on mains-pressure systems.
Shower Head options: Electric showers work with a handset and hose. Thermostatic valves can run larger fixed shower heads, including rainfall heads and dual-outlet setups.
Temperature stability: Both offer protection, but thermostatic valves handle pressure fluctuations elsewhere in the house more gracefully.
Appearance: Electric showers involve a visible wall-mounted unit. Thermostatic valves can be fully concealed behind the wall for a minimal look.
Installation trade: Electric showers need an electrician as well as a plumber. Thermostatic showers are usually a plumbing job only.

Your Plumbing System Is the Deciding Factor

Before comparing features, work out what system you have. This narrows the choice more than anything else.

Combi Boiler

A combi heats water on demand at mains pressure and has no storage cylinder. This is close to ideal for a thermostatic shower - you get strong, consistent pressure and effectively unlimited hot water. An electric shower would work here too, but you'd be paying to heat water electrically when your boiler could do it more cheaply.

Gravity-Fed System (Attic Tank and Cylinder)

Very common in Irish homes, particularly anything built before the 2000s. Water pressure comes from the height of the attic tank above the shower, which often means low pressure - especially on upper floors where the drop is small. A thermostatic shower can work well here, but you may need a shower pump to get satisfactory flow, and you'll want a valve specified as suitable for low pressure. An electric shower sidesteps the issue entirely, since it runs off the cold mains rather than the tank.

Unvented or Pressurised Cylinder

These store hot water at mains pressure, giving you both good flow and a decent volume of hot water. A thermostatic shower is the natural fit, and this setup handles larger rainfall heads comfortably.

Running Costs Compared

There's no universal answer here, because it depends on how your water is heated in the first place.

An electric shower draws a substantial load while running - around 9 to 10kW for most models - but only heats exactly the water you use, with no standing heat losses from a cylinder. If your alternative is switching on an immersion to heat a full tank for one short shower, the electric shower will often work out cheaper.

If your water is heated by gas, however, a thermostatic shower usually costs less per shower, since gas is typically cheaper per unit than electricity. The caveat is flow rate: a powerful thermostatic shower with a large head can use considerably more water per minute than an electric shower, which offsets some of that saving.

Electricity and gas rates move around, so it's worth doing the sum against your own current tariff rather than relying on general figures.

Safety and Temperature Control

Thermostatic valves are the stronger choice where scalding is a concern - households with young children, elderly relatives or anyone who might not react quickly to a sudden temperature change. The valve holds its set temperature and shuts off on loss of cold supply, and many include a maximum temperature stop that can be set during installation.

Electric showers aren't unsafe by comparison. They include thermal cut-outs that shut the unit down if it overheats, and better models offer more stable temperature control than budget units. But the protection is less comprehensive than a properly specified thermostatic valve.

Installation and Maintenance

Installing an Electric Shower

This is a job for a qualified electrician as well as a plumber. An electric shower needs its own dedicated circuit from the consumer unit, correctly sized cable for the unit's rating, RCD protection, and an isolating pull-cord switch. If your existing consumer unit doesn't have capacity, that adds cost. Don't treat this as a DIY replacement even when you're swapping like for like - cable sizing matters and gets checked.

Installing a Thermostatic Shower

Usually simpler, and normally plumbing work only. You have two routes. An exposed valve mounts on the wall surface with visible pipework, making it the easier retrofit. A concealed valve is built into the wall with only the controls and outlet showing - cleaner to look at, but it means opening up the wall, so it suits a full renovation rather than a straight swap.

Limescale and Hard Water

Hard water affects both types. Electric shower heating elements scale up over time and eventually fail, while thermostatic cartridges can stiffen or stick. In either case, descaling the showerhead regularly helps, and it's worth checking that replacement parts are available for whatever you buy.

Which Should You Choose?

As a rough guide:

Choose an electric shower if you have a gravity-fed system with poor pressure and don't want a pump, you need hot water independent of the boiler, you're fitting a second bathroom or ensuite that would strain your hot water supply, or you want the simplest option for an attic or garage conversion.
Choose a thermostatic shower if you have a combi boiler or unvented cylinder, you want strong flow and a larger rainfall head, temperature stability and scald protection matter in your household, or you're renovating and want a concealed, minimal finish.

If you're mid-renovation, it's worth deciding this early - the choice affects your shower enclosure and shower tray selection, and concealed valves in particular need to be planned before tiling.

Frequently Asked Questions

Can I replace an electric shower with a thermostatic one?

Sometimes, but not always straightforwardly. An electric shower only has a cold feed, so a hot supply needs to be run to the location - which usually means opening up walls or floors. You also need to confirm your hot water system can deliver adequate pressure and volume. A plumber should assess it before you buy.

Do I need a pump with a thermostatic shower?

Only on a gravity-fed system where pressure is too low for the valve to perform. If you have a combi boiler or an unvented cylinder, you won't need one. Some thermostatic valves are rated for low pressure operation, so check the minimum pressure requirement before assuming a pump is necessary.

Is a higher kW electric shower always better?

A higher rating gives better flow, but it also draws more current - which means your electrical supply and cabling have to support it. There's no benefit in buying a 10.8kW unit if your consumer unit can't accommodate it, so check with an electrician first.

Why does my electric shower feel weaker in winter?

Incoming mains water is colder, so the unit has to work harder to reach your set temperature and reduces flow to compensate. This is normal behaviour rather than a fault, though a higher kW model will be less affected.

What's the difference between a thermostatic shower and a mixer shower?

All thermostatic showers are mixer showers, but not all mixers are thermostatic. A manual mixer blends hot and cold in whatever ratio you set and won't correct itself if pressure changes. A thermostatic valve actively maintains your chosen temperature and shuts off if the cold supply fails.

Shop Showers at Bathroom Outlet

We stock a full range of showers to suit every system and setup - from electric showers for homes needing hot water on demand, to thermostatic shower valves in both exposed and concealed formats. You'll also find complete shower sets, riser rail kits, and bath shower mixer taps if you're showering over a bath.

Not sure which type your plumbing will support? Contact our team and we'll talk it through with you.

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