An unvented cylinder is a pressurised cylinder which is fed from the cold water mains through a pressure reducing valve and be heated directly via an immersion heater or indirectly via a boiler, heat pump or similar.
The stored hot water sits in the hot water cylinder under pressure and when a hot outlet opens, the water comes out at pressure and is replaced from the cold mains entering through the cold feed to the cylinder.
The unvented cylinder is extremely flexible and can be powered by renewable energy sources such as solar, heat pumps and certain biomass boilers.
As it is a pressurised system, unvented hot water cylinders must be fitted by a G3 qualified installer and serviced annually. This is to ensure all aspects of the pressurised system are working efficiently and most importantly, safely. They also have a discharge pipe from the relief valves which must be installed as per strict guidelines in copper or a suitable high temperature material.
Unvented cylinders offer a number of benefits
- Hot water is stored at a lower temperature – approximately 60 degrees
- Mains Pressure at all hot and cold outlets
- Extremely efficient – especially copper unvented hot water cylinders
- Work well with Heatpumps – especially when fitted with high efficiency copper coil
- Longer warranty due to annual service
Thermal stores take a completely different approach to delivering hot water.
Rather than drawing from the stored hot water, the thermal store forces the mains pressure cold water through a high efficiency heat exchanger coil which draws its heat from the surrounding “Thermal Store” to heat the water for the taps.
The thermal store approach offers a number of benefits depending on the application:
- Extremely energy efficient reducing running costs
- Can be used with Solid Fuel
- Can run central heating from the thermal store
- Instant hot water and heating
- Extremely reliable as there are fewer mechanical components
- Easy to install
- No annual maintenance
- Fresh mains water at hot and cold taps
- Zero legionella risk as no stored water is fed to taps
When to use a thermal store?
- When incorporating a solid fuel energy source such as an AGA or woodburning stove
- When using multiple fuel sources
- In rural locations
- In high rise developments where mains pressure is required without the discharge complications of Unvented