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Hot water cylinders are continually increasing in popularity and can now be found in most homes across the UK. They are commonly used to ensure that a copious amount of stored hot water is available on demand for a multitude of domestic uses. Unvented cylinders are connected directly to the mains water system so there is no cold water tank, which means they offer high water flow rates to provide higher water pressure for showers and baths.
An unvented cylinder is heated by either immersion heaters (a direct model) or by a heat source located outside the vessel such as a boiler or wet solar system (an indirect model).
Unlike vented cylinders, there isn’t a vent pipe or tank to cope with excess water as it heats and expands. To remedy this unvented cylinders have inbuilt safety features like an expansion unit at the top or an air bubble that is inserted at installation.
The installation of an unvented cylinder is considerably less hassle as it can be placed anywhere in your home and, with no water tank needed, doesn’t take up as much physical space.

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Advantages
- No need for a water tank so the system takes up less space, giving you flexibility with where to install it.
- Tend to provide stronger water pressure (depending on the strength of the mains).
- No need for a tank of water that could freeze in winter or be contaminated.
- Quieter Performance
- Last's 30 plus years
Disadvantages- More expensive to install and maintain.
- If the water supply is turned off there will be no hot water.
- Not always compatible with modern power showers and mixers.
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If you would like some further advice on unvented cylinders and whether or not you would benefit from one, then please give us a call.
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Hot water cylinder capacity varies between 75 and 400 litres for domestic supply. The below figures are used by industry professionals as a guideline to the size cylinder you would require:
Bedrooms Showers/Bathrooms Indirect (litres) Direct (litres) 1 1 75/120 120/150 2 1 150 180 3 2 180 201 4 2 210/250 250/300 Larger Properties 300+ 300+ -
Here are a few brands and models of unvented hot water cylinders we recommend.
Cylinder Model/ Brand Sizes Available (volume in litres) ErP Rating (Energy Efficiency) Heating Method Warranty Megaflo Eco by Heatrae Sadia 70 / 125 / 145 / 170 / 210 / 250 / 300 B Indirect or Direct Lifetime Greenstore by Worcester Bosch 90 / 120 / 150 / 180 / 210 / 250 / 300 B Indirect Only 25 years Vitocell 200-V by Viessmann 90 / 120 / 150 / 180 / 210 / 250 / 300 C Indirect but includes a backup immersion heater 25 years against corrosion StainlessLite by Gledhill 90 / 120 / 150 / 180 / 150 / 300 / 400 C Indirect or Direct 25 years Tempest by Telford 90 / 125 / 150 / 170 / 200 / 250 / 300 C Indirect or Direct 25 years -
How it works
Getting started with boilerPRO is as simple as 1,2 3!
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Step 1Reach out to our team
Book your repair, installation or survey using on onsite forms, live chat or calling our team on 0800 810 1112
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Step 2Await our visit
Our professional team of engineers will be at your property to survey and in most cases, get started with the work.
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Step 3Relax and enjoy!
Whether its a new install or just a fix – we’ll leave your property with high performing heat and hot water.
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Let's get your unvented cylinder installed!
If you would like some further advice on unvented cylinders and whether or not you would benefit from one, then please give us a call.
