Direct Unvented Hot Water Cylinders | Mains Pressure Hot Water — No Boiler Required

A direct unvented cylinder stores and heats mains-pressure hot water using one or more built-in electric immersion heaters — no boiler, no flue, and no cold water tank in the loft needed. Cold water enters directly from the mains, is heated by the immersion element inside the cylinder, and is stored ready for use at full mains pressure. The result is powerful, consistent hot water at every tap and shower in your home.

Do You Need a Boiler?

No — and that's the key advantage of a direct unvented cylinder. Because it heats water purely with electricity, a direct unvented cylinder is a completely self-contained hot water solution. It's ideal for properties without gas, off-grid homes, flats, or anyone who wants to decouple their hot water from their heating system entirely. If you do have a boiler and want it to also heat your hot water cylinder, you'd be looking for an indirect unvented cylinder instead, which has an internal coil connected to your central heating circuit.

How It Connects

Installationof Direct Unvented Cylinder is straightforward in principle. Cold mains water feeds into the bottom of the cylinder via a dedicated supply. A pressure reducing valve (PRV) is fitted to control incoming mains pressure, along with an expansion vessel and a temperature and pressure relief valve (TPRV) — all of which are required by regulations for safety. Hot water then exits from the top of the cylinder and is distributed around the property. The immersion heater element(s) connect to a dedicated electrical circuit from your consumer unit, typically on a 16A or 20A circuit for a single element.

⚠️ A Few Things to Check Before Buying

Unvented cylinders must be installed by a G3-qualified engineer under Part G of the Building Regulations — this isn't a DIY job. You'll also need adequate electrical capacity for the immersion heater(s); a standard 3kW element draws around 13 amps, while a twin-element cylinder with a 3kW boost element will need its own dedicated circuit. Some cylinders also offer dual-tariff wiring, allowing you to take advantage of cheaper overnight electricity rates such as Economy 7.

Browse our direct unvented cylinders below — or contact our team if you need help sizing the right cylinder for your household demand.