An unvented hot water cylinder is worth considering if your showers are weak, hot and cold pressures don’t match, you have more than one bathroom, or you’d like to get rid of cold water tanks in the loft. It stores hot water at mains pressure, so several taps and showers can run at once with strong flow.
It only works well if your incoming mains water pressure and flow are good enough, so that’s the first thing an installer should measure. Our unvented hot water page explains how we assess homes.
Vented vs unvented: the difference
| Vented cylinder | Unvented cylinder | |
|---|---|---|
| Water supply | Fed by a cold water tank in the loft | Fed directly from the mains |
| Pressure | Depends on tank height (often low) | Mains pressure |
| Loft tanks | Yes | No |
| Showers | Often need a pump | Usually strong without a pump |
| Safety devices | Simple | Several, and must be checked annually |
Signs your home would benefit
- Weak showers, especially upstairs where the loft tank is only a short height above
- Unbalanced hot and cold pressure, making mixer showers hard to set
- Two or more bathrooms used at the same time
- An old loft tank that’s rusty, dirty or taking up space you’d like to use
- Plans for a loft conversion, where the tanks need to go
- A shower pump that’s noisy or failing
When an unvented cylinder isn’t right
It’s not the answer for every home:
- Low mains pressure or flow means an unvented cylinder won’t deliver its benefits
- Only one bathroom and small household may be well served by a combi boiler instead
- No suitable discharge route, as the safety discharge pipe needs a proper route to a safe outlet
- Old pipework may need upgrading to handle mains pressure
What installation involves
An unvented cylinder installation typically includes:
- Measuring mains pressure and flow at the property
- Choosing a cylinder size to match the household’s hot water use
- Fitting the cylinder with its safety controls, expansion vessel and pressure-reducing valve
- Running a discharge pipe (tundish and pipework) to a safe termination point
- Removing redundant loft tanks and capping old pipework
- Commissioning and registering the installation
Unvented cylinders must be installed by someone qualified in unvented hot water systems, and the work is notifiable under Building Regulations (Part G).
Annual checks matter
An unvented cylinder stores hot water under pressure, so its safety devices need checking every year. The service typically covers the pressure relief and temperature relief valves, expansion vessel charge and the pressure-reducing valve. It’s often done alongside the annual boiler service.
Unvented cylinders with different boilers
An unvented cylinder can be heated by a system or regular boiler, and often has an immersion heater as a backup. In off-grid homes around Worcestershire, it works with oil boilers and LPG boilers just as well as mains gas. It’s also a common part of a heat pump installation.
Unvented hot water in Worcestershire homes
In older homes around Worcester, Malvern and Droitwich, gravity-fed systems with loft tanks are still common. Where mains pressure is good, swapping to an unvented cylinder can transform showers and free up loft space, especially as part of a bathroom renovation.
Frequently asked questions
How big an unvented cylinder do I need?
It depends on the number of bathrooms and people in the home. An installer should size it based on your hot water use rather than using a standard size.
Can I have an unvented cylinder with a combi boiler?
Not usually. Combi boilers heat water on demand and don’t use a cylinder. An unvented cylinder normally works with a system or regular boiler.
Do unvented cylinders need servicing?
Yes. The safety devices should be checked annually by a qualified engineer, and it’s usually a condition of the manufacturer’s warranty.
Find out if your home is suitable
Fancy stronger showers and better hot water? Send us a message and we’ll check whether an unvented cylinder suits your home.