Electric Hot Water Cylinders for Homes With No Gas

What makes a cylinder electric

Most cylinders in houses with gas are indirect: a coil inside carries hot water from the boiler, and an immersion element is there as a backup. An electric cylinder, usually called a direct cylinder, has no coil in use. The immersion elements are the only heat source, so they are sized and positioned to do all the work.

That changes a few things. Heating is slower than a gas boiler through a coil, so the cylinder has to hold enough hot water to cover the day. The elements do far more hours, so element life matters more. And the running cost depends almost entirely on your electricity tariff and on how well the tank holds its heat. If you are not sure which kind you have, our guide to direct vs indirect hot water cylinder shows how to tell from the pipework and the label.

The options for a home with no gas

Four set ups cover almost every all electric home in London. Which one fits is decided by the building as much as by preference.

A direct unvented cylinder is fed straight from the cold mains and delivers hot water at mains pressure. It gives the best showers where the incoming supply is good. It also needs a pressure reducing valve, an expansion arrangement, relief valves and a discharge pipe through a tundish to a safe point outside, and it must be fitted by someone qualified for unvented work and notified to building control. It then needs an annual service.

A direct vented cylinder is fed from a cold water tank above it. In flats this is often a combination cylinder, with the cold tank built onto the top of the hot cylinder in one unit. It has no pressure relief discharge to route and fewer safety controls to maintain, but the pressure at the taps depends on the height of the tank above them, which in a flat is not much.

A thermal store, such as the Pulsacoil fitted in many purpose built blocks, holds a tank of heat rather than a tank of drinking water and heats mains water as it passes through. It gives mains pressure without being an unvented cylinder, which is why it suits flats with no discharge route. Our comparison of thermal store vs unvented cylinder covers the trade offs.

A heat pump cylinder is heated mainly by a heat pump, with an immersion for backup and for the weekly high temperature cycle. It is only an option where a heat pump can be installed, which rules out many flats. Our guide on the heat pump cylinder explains what changes.

• Direct unvented: mains pressure, needs a discharge route, G3 installer and annual service
• Direct vented or combination cylinder: simpler, lower pressure, no discharge pipe
• Thermal store: mains pressure, open vented, more parts between store and tap
• Heat pump cylinder: lowest running cost where a heat pump is possible

Economy 7 and off peak cylinders

If your flat is on Economy 7 or a similar off peak tariff, the cylinder should be built around the cheap hours. That usually means a larger volume, so a night of heating lasts the following day, good factory insulation, so the heat is still there in the evening, and two elements.

The bottom element heats the whole tank during the cheap window. The top element heats only the upper part and is used as a short daytime boost when the tank runs low, so you are not paying the day rate to heat the full cylinder. The controls matter as much as the cylinder: our guides to the dual immersion heater and the immersion heater timer explain how they should be set up, including the common mistake of a timer still set to winter hours in summer.

A single element cylinder on an off peak tariff works, but any top up during the day heats from the bottom and costs more. If you have one and the hot water runs out by the evening, the answer may be controls or capacity rather than a fault. Our page on hot water runs out quickly helps separate those.

Choosing the size

Because an electric cylinder recovers slowly, sizing it too small is the most common and most expensive mistake. A gas heated cylinder can be reheated in well under an hour. A direct cylinder on one element takes much longer, and on an off peak tariff you may only want it heating overnight.

Size it on how many people shower or bathe in the same part of the day, how many bathrooms can run at once, and whether you are on an off peak tariff. Then check it physically fits the cupboard with room to service the elements and valves. Our guide on what size hot water cylinder do I need works through the numbers by household.

Is a direct unvented cylinder right for a flat?

It can be, and it is often the best upgrade in a flat that has one. The two questions to answer first are the mains supply and the discharge route.

An unvented cylinder can only deliver what the incoming mains provides. Measure the flow and pressure at the kitchen tap before choosing; if it is weak, the new cylinder will be weak too. The discharge pipe must run from the relief valves, through a visible tundish, to a safe termination outside. In the middle of a block that route may pass through a neighbour's property or a common area, or may not exist, and in a leasehold flat the freeholder may need to agree to any new opening in an external wall.

If both questions have good answers, a direct unvented cylinder is a sound choice. If they do not, a thermal store or a vented combination cylinder is usually the practical option. Our page on unvented cylinder installation explains what a proper installation includes.

An unvented cylinder fitted without a lawful discharge route, or by someone not qualified for unvented work, is a safety problem and can cause trouble when the flat is sold. Ask to see the installer's unvented qualification and where the discharge pipe will go before work starts.

Keeping an electric cylinder running well

In London the enemy is scale. It builds on the immersion elements, slows heating, makes the cylinder noisy and shortens element life. Choosing Incoloy or titanium sheathed elements rather than copper when they are replaced makes a real difference; our guide to which immersion heater do I need covers the options.

Keep the stored water at about 60 degrees so that Legionella cannot grow, and resist the temptation to turn the thermostat right up to make a small cylinder last longer. If the tank is too small for the household, a hotter setting only adds scale and scalding risk. An unvented cylinder also needs its annual service, which checks the relief valves, expansion vessel charge and pressure reducing valve.

Get the right electric cylinder for your home

We repair and replace electric cylinders, thermal stores and unvented cylinders across London, and we will tell you if a repair is the better value before recommending a new one. Tell us what you have now, whether you are on an off peak tariff, and how many people use the hot water, and we can come prepared.

Call 020 4652 5111 to book. Our rates are on the pricing page and are agreed before we attend.