A variety of cylinders exist for older and more modern setups, with different configurations for different heating systems and energy sources.
These are heated via an internal coil connected to an independent heat source, most commonly a boiler.
These are heated electrically via an immersion heater
TRADITIONAL VENTED CYLINDER AND HEADER TANK
If you have an older heating and hot water system, you will likely have a cylinder like this lurking in an airing cupboard and a header water tank in your loft to provide a simple cold water store and pressure supply.
The components for this system are still readily available, these are great low maintenance systems, great on water volume but poor on water pressure.
This can be remedied by installing a pump to the system, in some instances a pump may not be ideal due to vibration and operation noise.
These cylinders can come with multiple coils, allowing for different heat sources. From Solid fuel to renewable energy.
PRESSURISED CYLINDER AND EXPANSION VESSEL
A Pressurised or Unvented Cylinder is connected directly the mains water supply. This means it will run at a higher pressure without the need of a cold feed tank.
These also have options for multiple coils driven by boilers, solar thermal and other modules.
The one pictured is a direct cylinder, being heated via the two immersion heaters connected on the side of the unit.
With the use of two immersion heaters it is ideal to take advantage of low rate electricity tariffs such as economy 7 or variable rate plans such as Agile Octopus.
Thermal stores turn the hot water cylinder concept on its head. Traditionally your boiler heats the hot water in the cylinder, which is then piped directly to your hot taps.
With a thermal store your boiler or other heating source is tasked with heating and maintaining the temperature of water in the cylinder and that water remains in the cylinder permanently. Both heating and hot water supplies are run through heat exchanging coils inside the thermal store to heat the water running through the pipes.
This provides the benefit of your hot water running hotter for a much longer period, without the limitations of a combi boiler.
They can also be a more modern approach to making use of off peak energy savings without the complexity or inefficiencies of storage heaters and also providing hot water to taps.
Off peak tariffs such as economy 7 or newer smart tariffs such as Agile Octopus can be leveraged for greater cost savings.
They are also ideal for making the best use of renewable heating sources such as thermal solar or solar panels with the use of immersion heaters or electric boilers.