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Unvented Cylinders
- Bespoke coil positioning and sizing for heat pumps, solar thermal, biomass, and multi-fuel systems
- Custom dimensions to fit awkward plant rooms or tight access routes
- Specific connection configurations and port positioning to match existing pipework
- Choice of stainless steel 316L or copper construction
What is an Unvented Cylinder?
- Delivers water from mains supply
- Does not require a separate cold water tank
- Allows for stronger water pressure and quicker heating times
- Can be heated using immersion or external heat sources
An unvented hot water cylinder is a sealed, pressurised storage vessel that delivers mains-pressure hot water throughout your property without requiring a cold water tank in the loft. Unlike traditional vented systems that rely on gravity-fed water, unvented cylinders provide consistent high pressure to multiple outlets simultaneously.
Why Choose Unvented Cylinders?
Unvented cylinders are the modern standard for UK properties, offering:
- High water pressure – Mains pressure (2-3 bar) ensures excellent flow to showers and multiple taps
- Space saving – No header tank needed, freeing up loft space
- Flexible installation – Can be installed anywhere in the property
- Renewable energy compatible – Works with heat pumps, solar thermal, and modern boilers
Unvented cylinders are designed to work at a high pressure and offer superior flow rates. This is beneficial as it allows high water pressure for a power shower and the ability to feed several outlets.
We manufacture unvented cylinders in both copper and stainless steel which both offer their own unique advantages.
Unvented hot water cylinders have no need for a cold water feed tank and with it being supplied directly from mains water, it offers far greater flexibility than a traditional vented unit. With the unit not requiring a gravity feed or pump it can be placed anywhere in the premises.
Flexibility
Unvented water cylinders also have the flexibility to work on a wide variety of systems; they can be fitted with coils for solar heating, heat pumps and underfloor heating. As all units are manufactured in-house, they can be made to bespoke customer specifications such as tapping size and positioning.
A range of standard sizes and formats is available in the Size and Specification tab. Alternative heights from 600mm to 2,000mm and diameters from the list are also available where space and water volumes are at a premium.
Advantages of Unvented Cylinders
- No extra storage needed
- Versatility
- Energy Efficiency
- Consistent hot water supply
The benefits of an unvented cylinder considerably outweigh the disadvantages.
One of the main advantages is that no cold water storage tank (like a header tank) is required in the system. This means homeowners can save space.
Another key advantage of unvented cylinders is their versatility. This is achieved through the possibility of using multiple heating sources. Unvented cylinders are also more efficient than vented systems, especially when used with modern boilers or heat pumps.
Due to their high water pressure, unvented cylinders benefit from a consistent supply of hot water. This makes them suitable for homes with multiple bathrooms, as well as commercial buildings with a high hot water demand. When unvented hot water cylinders are optimised properly, the recovery time and energy efficiency ensures hot water is readily available.
Copper
Copper has been renowned for its excellent antibacterial and antimicrobial properties for centuries; copper will eradicate E-Coli, MRSA, Avian Flu, Legionella and 99% of bacteria within just 5 hours of contact.
Copper is one of the most efficient conductors of heat. It has a thermal conductivity of 401W/mK.
Due to recent surges in copper prices, cylinders made from this material can be restrictively more expensive than their stainless steel alternatives.
As copper is a very flexible material, it allows for a wide range of customisation options. Generally speaking, if a bespoke specification isn’t possible in stainless steel, it’s probably possible in copper.
>Copper is valuable as scrap as it's an elemental metal. This makes recycling copper easy and cost-effective.
Copper is perfectly suitable for pressurised systems however its softer tensile strength means thicker copper material is required to withstand higher pressure resulting in increased costs; it also can not reach the high pressures of a comparable stainless steel units.
Copper is a raw material that is more costly than stainless steel and is suceptible to price volatility in the market.
Both copper and stainless steel are very resistant to corrosion when holding pH neutral water.
Private water sources however, tend not to be neutral, so cylinders in either material can corrode prematurely.
Stainless Steel
Although Stainless Steel is still perfectly safe for use, tests have concluded that bacteria takes longer to deteriorate on a stainless steel surface than a copper one.
Stainless steel has a much lower thermal conductivity than copper at just 14w/mK; this means that there is less heat transferred, but we compensate for this by specifying appropriately-larger coils.
Stainless Steel cylinders are by far the more cost-effective to purchase however their lower thermal conductivity and therefore surface area may result in higher costs in the long term.
The downside of the high tensile strength of stainless steel is that it is a more difficult material to work with; coils can not be wound as tight and require more lengths of tube for a suitable thermal transfer and therefore the sizes and types of unit we can make are more limited.
As stainless steel is an alloy, it requires separating into its key elements before it can be recycled, this is a more difficult and more costly process so usually will need to be disposed of at a recycling centre.
With stainless steel being a stronger material, stainless cylinders can withstand a higher pressure than copper with the same material thickness; resulting in stainless being suited to pressurised or unvented units requiring a higher pressure.
Although stainless steel cylinders have an initially lower upfront cost, the slight reduction coil conductivity could make them slightly more costly to run. However, when you also consider that slightly less heat will conduct through their walls, everything probably balances out quite equally.
Both copper and stainless steel are very resistant to corrosion when holding pH neutral water.
Private water sources however, tend not to be neutral, so cylinders in either material can corrode prematurely.
| Size | 80 - 1,150 litres |
| Primary Max Working Pressure | 3.5 BAR |
| Pressure Reducing Valve Pre-Set | 2.1 BAR |
| Expansion Relief Valve | 3.5 BAR |
| Combined Temperature & Pressure Reducing Valve | 4.5 BAR |
| Max Working Pressure | 3.5 BAR |
| Max Water Pressure (Before PRV) | 12 BAR |
| Immersion Heater Rating | 3kw 240V AC |
| Size | 90 – 2,000 litres |
| Pressure Reducing Valve – Max Inlet | 12 BAR |
| Operating Pressure | 3 BAR |
| Expansion Vessel Charge Pressure | 3 BAR |
| Expansion Relief Valve Setting | 6 BAR |
| Pressure & Temperature Relief Valve – Pressure Setting | 7 BAR |
| Pressure & Temperature Relief Valve – Temperature Setting | 90°C |
| Energy Cut-out Thermostat Setting | 80°C |
| Primary Heat Exchanger – Max Working Pressure | 6 BAR |
| Solar Heat Exchanger – Max Working Pressure | 6 BAR |
| Immersion Heater Rating | 3Kw – 240V AC |
Coils
We utilise a high surface area finned copper tube in our copper unvented cylinders for use with a Solar or Heat Pump system which operate at a lower temperature, and a stainless convoluted tube with our stainless steel cylinders. As the stainless tube does not have as high surface area, we utilise a larger coil to match the surface area of its copper counterpart.
Components
Combined Pressure Reducing Valve & Expansion Valve
Reduces the pressure of the incoming cold water feed to 3.0 BAR as well as allowing connection of an expansion vessel.
Temperature & Pressure Relief Valve
Set to relief pressure should the tank reach 7.0 BAR or 90°C.
Expansion Vessel
Supplied at a suitable size relative to unit volume; contains an internal rubber expandable membrane to facilitate increase and decrease of pressure inside the cylinder.
Plastic Tundish
Allows for audible and visual inspection of water being expelled from the pressure relief valve indicating a fault.
Immersion Heater
Electric immersion heater to provide backup heating, available in 3, 6, 9, and 12kw.
Dual Thermostat
Combined high limit and control thermostat for use with a boiler system.
Single Check Valve
Spring-loaded non-return valve to prevent backflow.
Drain Valve
Allows for easy drain down of the tank without needing to remove the cold feed pipe. Useful for when replacing immersion heaters.
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