Hot Water System

There are different ways to heat the water in your home. To help you understand hot water systems we have broken them down into the three main types of system.

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, unvented and instantaneous. But what do these terms mean and how do they work?

Open vented hot water systems

This system uses a selection of 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. The heat source can be gas or electric. The gas heats the water in a coil that passes through the hot water cylinder and the heat is passed into the water – like a big kettle. If it is electric then there is an element (immersion heater) inside the hot water cylinder that heats the water. This is usually less efficient.

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 cold water storage cistern and operate at a much higher pressure than the open vented system.

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 electric versions use a coiled heating element to heat the water rapidly in a similar way to a kettle or immersion heater.

The most common method to heat water is the use of a combination boiler sometimes referred to as a combi), 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.