The choice between a vented vs unvented cylinder affects how stored hot water reaches taps and what the installation needs around it. A traditional vented cylinder uses a storage cistern and gravity, while an unvented cylinder receives mains water. Unvented hot water is pressurised, but that does not mean every property achieves the same shower performance. Understand supply, storage and safety constraints before choosing a replacement or conversion.
Gas Safe registered 25 years in the trade 12 years running the business
Written by Chris Gill, C Gill & Son Plumbing & Heating ·
How a vented cylinder supplies hot water
A traditional vented cylinder receives cold water from a storage cistern, commonly in the loft. The height difference between its water level and an outlet creates available static pressure. The system also has an open vent arrangement that must remain correctly configured and unobstructed.
Performance depends on available head, pipe sizes, restrictions and outlets in use. A shower close to cistern level may behave differently from a downstairs tap. Some installations use suitable pumps, but compatibility and supply arrangements need assessment rather than assuming any pump can be added. Retaining a serviceable vented arrangement can be worth considering where its performance already suits the household; age of the design alone does not determine the right replacement.
How an unvented cylinder differs
An unvented cylinder stores hot water in a sealed vessel supplied from the mains, with required controls and safety provisions. It does not normally need the cold storage cistern feeding a traditional vented cylinder. That can release loft space and change layout options.
The supply still has limits. Incoming pressure, available flow, internal pipes and simultaneous demand influence performance. An unvented cylinder does not create unlimited water or automatically solve a restricted main. Investigate those conditions before promising better delivery at several outlets. Ask whether other equipment still uses the existing cistern before assuming it can be removed, and include any changes to cold-water distribution in the proposal rather than considering only the cylinder itself.
Pressure and flow are different measurements
Pressure describes the force available to move water; flow describes the volume delivered over time. A static reading with outlets closed does not show how the supply behaves with several taps running. Good-looking pressure alone is therefore insufficient to predict a satisfying shower.
Assessment should consider working pressure and flow under relevant conditions, alongside restrictions, valves and outlet requirements. For either cylinder type, ask what is expected at your chosen fittings rather than accepting high pressure as a complete specification. Stored hot water capacity does not remove a mains-flow restriction. Explain when several people use water together, and consider the cold supply to showers as well as the heated water coming from storage.
Safety provisions and qualified installation
Unvented storage needs expansion provision, temperature and pressure protection, and an appropriate discharge arrangement. These are essential design elements, not optional accessories. The route and termination of discharge pipework can affect whether a proposed location is practical.
Installation, servicing and safety-device work should be undertaken by someone competent and appropriately qualified for the cylinder system and applicable requirements. Vented systems also need correct installation and maintenance. Do not adjust safety valves, obstruct discharge pipes or alter vents yourself. Abnormal discharge and leaks need professional attention. This comparison does not claim any additional cylinder qualification for Chris; ask who will undertake the work and confirm the responsibilities for assessment, installation and servicing.
Need it sorted? Discuss hot water cylinder installation
Capacity should reflect demand, while recovery depends on the heat source and cylinder design. Both vented and unvented arrangements can use different heating methods; the supply category does not specify how stored water is heated.
A conversion assessment should cover supply, cylinder space, structural support, pipework, controls, discharge and redundant equipment. Discuss this through hot water cylinder installation. If the heat source is changing, explore boiler installation. Use the quote form to compare retaining vented storage with an unvented arrangement. Include your current system and the outlets you want to improve. A complete proposal should explain expected performance, any supply limitations and maintenance requirements before you decide which arrangement suits the home.
Covering Neath, Port Talbot, Swansea and the surrounding area.
Common questions
Vented vs Unvented Cylinder FAQs
Clear answers before you arrange a visit.
Will an unvented cylinder improve my shower?+
It may provide suitable delivery where the incoming mains supports demand, but cannot guarantee improvement with a restricted supply. Shower requirements, pipework and simultaneous use matter. Expected performance needs assessment before choosing.
Can a vented cylinder stay when the boiler is replaced?+
Potentially, if condition, capacity and compatibility suit the proposed arrangement. A new boiler does not automatically require unvented storage. Ask why retaining or changing the cylinder and its controls is recommended.
Does unvented storage mean no maintenance?+
No. Controls and safety provisions need attention under the manufacturer instructions and applicable requirements. Arrange appropriate professional servicing. Producing hot water does not prove that all safety devices function correctly.
Can an unvented cylinder go anywhere indoors?+
No. It needs suitable support, maintenance access, compatible pipe routes and an appropriate discharge arrangement. Removing the need for a feed cistern creates flexibility, not permission to use every cupboard.
