What are the main types of hot water systems?
Currently there are three main types of hot water systems in use in the UK; open vented, instantaneous and unvented.
Open Vented
This system uses many different parts to heat the water. It consists of a hot water cylinder, a cold-water storage cistern (tank), special pipework (known as an open vent pipe), and a heat source to heat the water. There are two types of open vented hot water: direct heating and indirect heating.
- Direct heating – the water is heated directly from the heat source either by an immersion heater or by the boiler.
- Indirect heating – the central heating and the hot water are separate. The water is heated via a coil (heat exchanger) from a boiler. This is done because there is a set of radiators connected to the boiler, in this case water in the central heating system slowly becomes contaminated by iron residues from the radiators which would make the hot water unusable for washing.
Instantaneous Hot Water Heating Systems
This method involves using gas or electricity to heat the water to a useable temperature without the need to store the water.
The most common method to heat water is the use of a combination boiler, this type of boiler works by using the circuit that powers the central heating and diverting it to another ‘water to water’ heat exchanger (heat swapping). This part swaps out the heat from the heating water to the hot water parts of your home.
Unvented Hot Water Systems
These systems are far more complicated and have many more parts to them but do allow near mains pressure hot water supply. They are designed to do away with the storage cistern and operate at a much higher pressure than the open vented system.
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