Hot Water · Glossary
Vented Cylinder
A hot water cylinder fed by gravity from a cold water tank in the loft, delivering low-pressure hot water without G3 regulation.
A vented cylinder is the traditional UK hot water store: an open-vent copper cylinder fed by gravity from a cold water storage tank in the loft. The vent pipe terminates over the loft tank, allowing expansion to escape safely. No G3 regulation applies, so any plumber can install or service.
Pros: simple, inexpensive, no annual safety inspection required, no risk of catastrophic pressure failure. Cons: weak shower pressure (relies on head height — typically 0.1 bar per metre of fall, so often only 0.3-0.5 bar at a first-floor shower), cannot easily integrate with mains-pressure outlets, and loft tank prone to contamination and freezing.
Most Cornwall replacements upgrade vented to unvented at the same time as a boiler swap, to gain mains-pressure showers. See our cylinder page.