A traditional vented system relies on a cold water tank in the loft, using gravity to push water down to your taps. That is why the shower upstairs is weak and why you need a pump to make it acceptable.
An unvented cylinder takes its supply directly from the cold water mains instead. Because the water is heated under mains pressure, it delivers to taps and showers at a much higher flow rate, with no pump needed.
What you actually get
Mains pressure showers. Proper pressure across several bathrooms at the same time without the flow dropping when someone else turns a tap on. This is the reason most people do it.
The loft back. No cold water storage tank and no expansion tank up there. That frees up real storage space, and it removes the single biggest water damage risk in most houses. It also makes a loft conversion possible where the tanks were previously in the way.
Cleaner water. Loft tanks collect dust, debris and occasionally worse. An unvented system is completely sealed, and the hot water comes from the same clean mains supply as your cold.
Silence. No tank refilling noisily in the middle of the night and no shower pump buzzing every time someone runs a tap.
Where it makes most sense
Larger properties with two or more bathrooms, particularly where several might be used at once. That describes a lot of housing around Horsham, Southwater, Leatherhead and Reigate.
It is also the right answer where a combi boiler cannot cope. A combi is limited by flow rate, typically nine to twelve litres a minute, and no combi can serve three simultaneous showers regardless of what its output figure says.
The one non-negotiable
Unvented cylinders must be installed and serviced by someone holding the G3 Unvented Hot Water qualification. That is a legal requirement, not a preference.
The reason is straightforward. These systems store a large volume of water well above boiling point, under mains pressure, held stable by safety devices. If those devices are fitted or maintained incorrectly, the failure mode is genuinely dangerous.
We hold G3 alongside Gas Safe registration, and we install and service unvented cylinders across West Sussex and Surrey.
Before you commit
The one thing worth checking first is your incoming mains pressure and flow rate. An unvented cylinder delivers hot water at whatever pressure your mains provides. If the incoming supply is weak, the cylinder cannot invent pressure that is not there.
We measure this at survey rather than assuming it, because it is the difference between a system that transforms your showers and one that disappoints you expensively.
Frequently asked
Do I legally need a G3 qualified installer?
Yes. Unvented cylinders operate under mains pressure and store a large volume of very hot water. It is a legal requirement in the UK that they are installed and serviced only by someone holding the G3 Unvented Hot Water qualification. We hold it.
Will an unvented cylinder work with my water pressure?
It depends on your incoming mains pressure and flow rate, and that has to be measured rather than assumed. If the incoming supply is weak, an unvented cylinder cannot manufacture pressure that is not there. We test before recommending one.
How is it different from a combi boiler?
A combi heats water on demand and is limited by flow rate, so it struggles with several outlets at once. An unvented cylinder stores a large volume of pre-heated water at mains pressure, so it can serve multiple bathrooms simultaneously. The trade-off is that it can run out and needs space.
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Relevant in:HorshamCrawleyLeatherheadReigate