How does a boiler heat water in your hot water cylinder?

Having hot water readily available in a house is an important contributory factor in creating a good standard of living for the occupants. Fortunately for the UK, the majority of its houses contain either a combination boiler, or a hot water tank or cylinder that distributes hot water around the home, once it has been heated by a boiler or other device.

Two common types of water cylinders are ‘direct’ and ‘indirect’. A direct cylinder stores water and heats it with an internal electric immersion heater. The most commonly implemented heating system, used in new houses, actually uses an indirect cylinder. In an indirect system a copper coil filled with hot water from the boiler passes through the inside of the cylinder. This heats the water inside it indirectly because no hot water from the boiler ever mixes with the water in the cylinder. The storage capacity of both cylinders allows them to provide hot water for several appliances simultaneously. This gives you the useful ability to wash up while someone else is enjoying a warm shower. A variation on the single coil cylinder is a twin coil cylinder. This uses two coils to heat a cylinder indirectly. There are several alternative ways to heat the water that passes through the copper coil, other than a gas burning system: solar panels and wood-burning stoves are common examples of these. A twin coil cylinder combines an environmentally-friendly system and a standard boiler to heat the water in the main cylinder indirectly. Using two coils means you can operate a more eco-friendly source and top up the heat where necessary with your gas or oil boiler. 

Both direct and indirect water cylinders can be vented or unvented. Unvented means that the cylinder uses the mains water pressure to push the water through to the outlets. A vented cylinder uses a tank in your loft to provide the water pressure needed to supply the water to your taps. If your heating systems utilise a solid fuel, such as wood or coal, then a vented cylinder is compulsory because you are unable to precisely control the heat going from the boiler to the cylinder. A vented cylinder will allow for any excess heat and pressure to be released through the header tank because it is unsealed.

When shopping for a cylinder there are many factors to consider. The most important thing is to consider all of the possible configurations and to find what makes the most sense to you, in terms of money and sustainability. Nobody likes being without the basic comfort of hot water so a sensible investment is recommended. We recommend you consult a professional installer before you buy. Check out the following sections of our website for the types of cylinder available.

Unvented Cylinder Pressurised Cylinders Vented Hot Water Cylinder Direct Hot Water Cylinders Indirect Hot Water Cylinders
Unvented Cylinder Pressurised Cylinders Vented Hot Water Cylinder Direct Hot Water Cylinders Indirect Hot Water Cylinders