If your home stores hot water in a cylinder rather than heating it on demand, you’ve got one of two types: vented or unvented. The difference isn’t just technical trivia — it affects your water pressure day to day, and it’s directly tied to a genuine safety requirement around who’s allowed to install it.

Vented Cylinders

A vented cylinder is fed from a cold water tank, usually in the loft, using gravity to move water through the system. It’s the traditional setup in a lot of older UK homes, and it’s simple, reliable, and low-pressure by design.

Unvented Cylinders

An unvented cylinder is fed directly from the mains, with no tank required, so you get strong, consistent water pressure throughout the house — the same pressure at every hot tap and shower, rather than depending on gravity and tank height.

Why the Installer’s Qualification Isn’t a Technicality

Here’s the part that actually matters: unvented cylinders are pressurised systems, and if installed incorrectly, they can be genuinely dangerous — not just “might leak,” but capable of serious failure under pressure if the correct safety devices and installation standard aren’t followed.

Because of this, installation must be carried out by an installer holding G3 qualification specifically — this isn’t a general plumbing qualification, it’s a distinct one covering unvented hot water systems and their required safety components. If an installer can’t confirm they hold G3, that’s not a minor gap.

Which One Should You Choose?

If you’re happy with your current pressure and your existing vented system is working fine, there’s often no pressing need to change it. But if you’re renovating, extending your bathroom setup, or simply tired of weak pressure upstairs, an unvented cylinder is usually the upgrade that solves it — provided your incoming mains pressure and flow rate can actually support it.

See our Hot Water Cylinders page for full detail on installation, or Get a Quote to get your current setup assessed.