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How do unvented cylinders work?

9 Answers

Answered by BoilerOne

29th May 2019

BoilerOne answered the question "How do unvented cylinders work?"

An unvented cylinder uses mains cold water at a set pressure to provide a balanced and higher pressure to hot and cold outlets. It also serves expansion via a vessel complete with pressure and temperature safety relief valves. A preferred option for larger hot water demands. It is important that the pressure and flow are checked prior to installing an unvented cylinder. BoilerOne recommend you consult a heating engineer with an unvented qualification to install your cylinder.

Answered by LP Plumbing & Heating Ltd

19th May 2019

LP Plumbing & Heating Ltd answered the question "How do unvented cylinders work?"

In a nutshell they are a sealed system (ie not open to the atmosphere) and work from water pressure rather than from flow rate like a combi boiler does. For an unvented cylinder to work properly they generally need a minimum of 3 bar incoming water pressure. So if we use the scenario that your incoming main to the house is at 4 bar pressure it will then hit a pressure reducing valve that regulates it to 3 bar, in theory this then means that your hot and cold water outlets will all be at equal pressure (however bad pipework runs and incorrect pipesizing can affect this). The biggest advantage of an unvented cylinder is that you can have multiple showers running at the same time without any of them losing pressure. Unvented cylinders also use an expansion vessel which can be internal or external alongside 2 safety devices called pressure relief valves, these are there to ensure that any excess pressure can be released safely in the event of failure in the system,these valves are always piped to the outside for safety and include a tundish so that you can see if there is water passing through (basically a visual aid to detect a fault).

Answered by A.D. Energy

17th May 2019

A.D. Energy answered the question "How do unvented cylinders work?"

Unvented systems are pressurised and are mains fed. The system has expansion vessels and various safety devices to protect the system. Pressure from these is much better due to being mains fed. You can also usually have multiple hot water outlets open without a reduction in pressure. Annual servicing is very important on these systems to ensure it's operating correctly.

Answered by PG Plumbing

26th March 2019

PG Plumbing answered the question "How do unvented cylinders work?"

Unvented cylinders work by using mains pressure direct into them . Normal vented cylinders are fed from a cold water tank normally in loft . The cylinder has a vent pipe coming from the hot and into the cold water tank , this is for expansion . Unvented cylinder do not have a vent pipe , they have expansion vessels to allow the natural expansion that occurs . As long as you have got good flow rates and pressure the unvented system will be far better . You will not need additional shower pumps and you can get rid of the cold water tank . But you might also need to achieve better flow rates to have an unvented cylinder fitted . This can be done by either having a new water main installed or using a booster pump

Answered by Garden City Services

23rd March 2019

Garden City Services answered the question "How do unvented cylinders work?"

The hot water cylinder doesn't need a vent pipe for expansion going into the loft and is mains fed from your cold water incoming mains from the street, therefore you will not need a cold water storage cistern in the loft. The cylinder is far superior to your conventional vented cylinder because the pressure will be amazing more throughout your house and will not fluctuate when multiple services are used, therefore allowing multiple shower outlets with high water flow rates to be used at the same time. These cylinders will need to have an annual service due to some safety valves and discharge pipe and general check, this is normally carried out at the same time as your gas boiler to save costs.

Answered by Heatwize plumbing and heating

15th March 2019

Heatwize plumbing and heating answered the question "How do unvented cylinders work?"

Mains pressure hot water storage. It's a store of hot water which is pressurised and mains fed. It means being able to have stored hot water in a tank but at mains pressure. So no need for cold water storage tanks. Best when there's more than one shower or bath in the property. The water is heated via an immersion heater (direct) or a boiler (indirect).

Answered by Fortune And Co Plumbing and Heating Ltd

1st March 2019

Fortune And Co Plumbing and Heating Ltd answered the question "How do unvented cylinders work?"

In a property with a mains pressure hot water system, all taps and water outlets attached to that system will have mains pressure at both hot and cold. in a property isn't difficult to understand that all cold taps or cold outlets are connected directly to the incoming water mains. Understanding where your hot water come from takes a little more technical understanding as it is still fed directly from the incoming mains water but then the water passes through equipment designed specifically for heating the water at high pressure. There are different methods of doing this and many interpretations on product design.

Answered by Beales Services

28th February 2019

Beales Services answered the question "How do unvented cylinders work?"

In an unvented hot water system, a cylinder is connected directly to the mains so there is no need for a cold water tank in the loft. The unvented cylinder is filled with cold water and kept under pressure from the incoming water supply. The cold water is then heated by either a boiler or electric immersion heater. Because water increases in volume as it gets warm, an unvented cylinder needs to include a mechanism that allows for this expansion to take place, thereby keeping the cylinder operating at a safe pressure at all times. The unvented cylinder will have outlet pipe work connected to it that will carry the hot water around the property to various outlets. As soon as a tap is opened the pressure of the incoming cold water forces the hot water in the cylinder out towards the opened outlet. Therefore, hot water is delivered to the tap or shower head at a pressure relative to the force of the incoming cold water mains pressure to the cylinder. Because unvented cylinders are limited by the pressure of the mains water supply that feeds them, it is important to check that there is adequate mains pressure at the property prior to installation, typically a minimum of two bar but preferably more.

Answered by PipeDream Plumbing

11th February 2019

PipeDream Plumbing answered the question "How do unvented cylinders work?"

Unvented cylinders are supplied directly off cold main supply, normally around 3 bar of pressure. This means means you have great pressure all the time at every outlet. Unvented systems will also have some kind of expansion vessel to accommodate the water as it heats up. A vessel basically a trapped volume of air, held by a rubber diaphragm within a steel vessel which is connected to the pipework, and as the water in the cylinder expands it is pushed into the expansion vessel, compressing the air within the diaphragm.

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