Electric water heater and boiler

No gas connection, no combustion, no flue to the outside. That is what these two devices share, and beyond it they do something entirely different.

The water heater makes hot water for your tap and your shower. The boiler heats your radiators or your underfloor circuit. If you need both, you need both; one does not replace the other.

The water heater: 150 litres on 2 kilowatts

The cylinder is the reserve and the power rating is the refill speed, and here those two sit far apart. 2 kW is modest against 150 litres.

What that means in practice: heating a fully cooled 150-litre cylinder to 70 °C takes roughly five hours at 2 kW. That is a calculation on mains water at around 15 °C with no heat loss, not a manufacturer figure, but the order of magnitude holds. As long as you do not empty the reserve in one go, you never notice; empty it and you wait.

So we look at how you draw hot water rather than at how many people live there. Two people showering at length one after the other load this cylinder harder than four who shower briefly.

The boiler: seven sizes from 4 to 24 kilowatts

This is the device that keeps your whole emitter circuit running. There are seven versions: 4, 6, 9, 12, 15, 18 and 24 kW, rated for roughly 50 to 280 m² of floor area.

Which size you need follows from a heat loss calculation, not from the square metres on your floor plan. Those areas are the manufacturer’s indication; a well-insulated home of 150 m² asks less than a poorly insulated one of 100 m².

Efficiency sits at 99.7%, and that figure beats a gas boiler for a simple reason: no heat disappears up a chimney.

That still does not make it cheap. Efficiency says how much of your energy reaches the water, not what that energy costs. A heat pump draws several kilowatt-hours of heat from one kilowatt-hour of electricity; an electric boiler never exceeds one. Per cubic metre of home you are heating more expensively here than with a heat pump.

Where it is the right choice: a home or a space where a heat pump cannot be sited, where there is no gas, or where the heat demand is so small or so brief that a heat pump never pays for itself.

What your consumer unit needs for it

This is the point at which an electric boiler falls over in practice, and it is exactly why the size matters. The heavier the version, the more current it draws. The lighter versions run on an ordinary three-phase supply of 3 x 25 A. Only the heaviest, the 24 kW, asks for more: 3 x 34.8 A and a 10 mm² supply cable.

If you have 3 x 25 A and land on a heavy version, upgrading is not the only way out. Insulating or adapting the emitter circuit often lowers the heat demand enough for a lighter boiler to do the job. Upgrading runs through your network operator and costs both time and money.

So we check your consumer unit and your connected load before anything is ordered. The exact connected load of the version that fits you is stated in the quote.

The water heater is far lighter: 2 kW on an ordinary 230 V circuit.

What we do, and what our supplier does

On these two devices we are your adviser, not your installer. We work out what suits your home, check your consumer unit, and explain what electric heating gains you and what it costs. Supply and installation run through our supplier, who does this work daily and has the trades for it.

That is a different role from solar panels, battery storage and charging infrastructure, where we handle the whole route ourselves. See how we work.

Why we advise on it all the same. Anyone wanting to come off gas rarely gets past the question of whether it is possible at all. An installer who sells gas boilers seldom employs electricians, so the electric route never comes up. That is the gap we fill: first establishing whether it fits your home and what it means for your supply, and only then the question of who fits it.

Alongside your panels

Both devices are a large electrical load, and that is exactly what makes them interesting once you generate your own power.

A hot water cylinder is the simplest form of storage there is: you put heat in while your solar panels are producing and take it out in the evening. The energy manager can shift the reheating to the hours when the power is your own or the tariff is low.