Is a Mixergy Smart Hot Water Cylinder Worth It?

Updated July 2026 · Emergency Plumber Chelsea

How a standard cylinder heats water. In a conventional hot water cylinder, a coil near the bottom carries hot water from the boiler, or an immersion element heats the water directly. Because hot water rises, the tank gradually fills with hot water from the top, but in practice the controls usually heat the whole volume before switching off. If you only need a little hot water, you still pay to heat the full tank. Our guide on how a hot water cylinder works explains the coil, the cylinder thermostat and the safety parts in more detail.

What Mixergy does differently. A Mixergy cylinder is designed to heat from the top down and keep a clear layer between hot water at the top and cold water below. That means a partly heated tank still gives you properly hot water at the tap, rather than a whole tank of lukewarm water. Sensors in the cylinder measure how much hot water is available, and the app shows it as a level, so you can see at a glance whether there is enough for a bath or whether to top it up. Heating can be scheduled, boosted from a phone and set to learn your usual pattern of use.

Heat sources it can work with. Depending on the model, a Mixergy cylinder can be heated by a gas boiler, by an electric immersion element, and in some versions by a heat pump or by surplus electricity from solar panels. That flexibility is a large part of the appeal: a household can heat water from the boiler in winter and from the panels on a sunny afternoon, or run the immersion on a cheap overnight tariff. Check which version suits your heat source before choosing, because not every model does everything.

Who gains most from a smart cylinder. The strongest cases are households with solar panels that export a lot of daytime power, homes on a time-of-use electricity tariff, homes planning to move to a heat pump, and households whose hot water use changes a lot, such as a family house that is sometimes full and sometimes nearly empty. Being able to heat a quarter of the tank on a quiet day, and the full tank before guests arrive, is where the design pays for itself. Our guide to immersion heater running costs shows why heating less water, at cheaper times, makes a difference if you rely on electricity.

When it is not worth it. If your existing cylinder is sound, heats well and has a working thermostat and safety valves, replacing it only to get smart features is hard to justify. If you live in a smaller flat with one bathroom, a combi boiler with no cylinder may suit you better and free up the cupboard; our guide to combi vs system boilers sets out that choice. And if the budget is tight, a good standard cylinder with a properly set thermostat and a modern programmer gets you much of the benefit for less.

Unvented or vented. Most new cylinders in Chelsea homes are unvented, fed directly from the mains, which gives good pressure at every tap and shower. Smart cylinders are made in unvented form, and some ranges also include versions for tank-fed vented systems, so check what is available for your setup. An unvented cylinder of this kind has to be installed by an engineer qualified for unvented hot water systems, the installation is notifiable under the Building Regulations, and it needs the same safety parts as any unvented cylinder, including a pressure relief valve discharging through a tundish. Our comparison of unvented and vented cylinders explains the differences.

Choosing the right size. Because a smart cylinder can deliver usable hot water from a partly heated tank, some households find they can manage with a smaller size than they would choose for a standard cylinder. That depends on how many bathrooms you have, how often baths are run back to back, and your mains flow rate. Sizing too small still leaves you short at busy times, so work it out properly rather than guessing. Our guide on what size hot water cylinder you need walks through the numbers.

Space, pressure and your home. Chelsea townhouses often have several bathrooms over four or five floors, which makes stored hot water a better fit than a combi boiler. A smart cylinder needs roughly the same cupboard space as a standard one of similar capacity, plus room for its controls and pipework. Mains pressure and flow still matter: an unvented cylinder can only deliver what the incoming supply gives it, so we check flow at the kitchen tap before recommending one. In mansion flats, check first whether hot water comes from a communal system, and whether the lease or managing agent restricts changes to cylinders and discharge pipes.

Smart cylinders and heat pumps. If you are thinking about a heat pump in the next few years, the cylinder decision is worth making with that in mind. Heat pumps work at lower temperatures and need a cylinder with a coil or heat exchanger designed for them. Buying a heat-pump-ready cylinder now can save replacing it again later. Our guide to heat pumps vs gas boilers covers whether a heat pump is realistic for your home.

What fitting one involves. Replacing a cylinder usually means draining the old one, disconnecting the boiler and immersion connections, fitting the new cylinder with its safety valves and discharge pipe, rewiring the controls, filling, commissioning and checking the discharge arrangement. Where an old vented cylinder with loft tanks is being replaced by an unvented one, the tanks can often be removed as part of the job. The work takes most of a day or more, depending on access and pipework, and there is no call-out fee on jobs over 3 hours.

Is it worth it for you? A smart cylinder makes the most sense when you need a new cylinder anyway and at least one of these applies: you have or are getting solar panels, you use a time-of-use tariff, a heat pump is on the horizon, or your hot water use varies a lot. If none of those apply and your cylinder is working, keep it, service it and set the controls properly. If you are unsure, a plumber can check the condition of your current cylinder, your mains flow and your heat source, and tell you which option fits.

Advice and installation in Chelsea. Call Emergency Plumber Chelsea on 020 3002 6667 to have your hot water system checked or a new cylinder fitted. We look at the existing cylinder, the mains supply, the space and your heat source before recommending anything, and we give you a clear price before work starts. See our plumbing installation service for cylinders and our boiler installation service if the boiler is being replaced at the same time. We cover SW3, SW10, Knightsbridge, Sloane Square, South Kensington and Fulham.

Quick tips

• Only consider a smart cylinder when your current one needs replacing, not as a straight upgrade.
• Check which model suits your heat source: boiler, immersion, solar diversion or heat pump.
• Have your mains flow rate measured before choosing any unvented cylinder.
• If a heat pump is likely in future, choose a cylinder that is ready for one now.
• In a mansion flat, confirm there is no communal hot water supply before planning a new cylinder.

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