Heating Systems

Different types of heating systems explained

Gravity hot water system

gravity fed hot water system

This is a traditional open vented system with gravity fed domestic hot water heating (DHW) and central heating that is pumped around the system. In this traditional open-vented design, the system is fed with water and kept under pressure via gravity-fed water from the main header tank in the loft. The hot water cylinder is heated simply via a gravity hot water circuit from the boiler, and central heating is provided via a separate pumped circuit from the boiler.

A separate header/expansion tank is used to feed the DHW to prevent the risk of contamination with the primary circuit water. If your water pressure is low, you might consider increasing it with a pump. These are especially useful when building a high flow-rate shower or wet room.

Fully pumped system

fully pumped system

Over the last 25 years in the UK the fully pumped, open vented system has become the number one choice of installation whether it's for new build or is a replacement system.

This is the standard open vented system as above with both the domestic hot water and central heating both controlled on the same single pumped circuit from the boiler (hence the term: "fully pumped system").

Such a system provides increased control over domestic hot water heating and quicker heating times which in turn leads to better system performance and increased efficiency.

Sealed system (vented DHW)

sealed vented hot water system

The sealed system is an ever increasingly popular type of heating system due to its simplified design. The system is fed and pressurised with water direct from the mains, then sealed. This eliminates the need for the system water feed tank and open vent pipe work in the loft.

This therefore simplifies and reduces the cost of the installation process and reduces maintenance requirements (there are less components to maintain!). In the diagram on the left a conventional tank-fed indirect hot water cylinder has been used with its own header tank in the loft. If you require additional heating in the summer, especially with Towel Warmers and Heated Towel Rails, an electrical element can be used to override the heater without turning on the Central Heating.

Sealed system (unvented DHW)

sealed unvented hot water system

"Unvented" system boilers (as opposed to "open/vented" systems) feed direct from the mains water supply and are supplied as a packaged unit comprising all the necessary controls and safety devices.

A mains pressure unvented domestic hot water cylinder is used and so all tanks/pipework are eliminated from the loft. The whole heating system is completely sealed (i.e. "unvented") which removes the risk of freezing pipes in the loft, does away with maintenance work in the loft and reduces the risk of system leakage.

Unvented sealed system boilers benefit the end user with increased flow rate on their domestic hot water to all outlets in the property as it is held at mains pressure.

Combination boiler

combination hot water system

A combination (or combi) boiler is like a standard unvented boiler, only with a second heating circuit (the domestic hot water circuit) to provide instant hot water on demand - thus the name 'combination boiler'. On an HRM combi the secondary circuit is fed directly from the mains water supply to the plated heat exchanger and so, as long as the boiler is firing, there is no limit to the amount of hot water that can be produced.

In an age where space is a highly sought after commodity, combination boilers are understandably becoming ever more popular. All water tanks in the loft and even the domestic hot water cylinder are done away and hot water is heated instantaneously, on demand by the boiler.

They are ideal for flats and smaller households with low/ infrequent hot water consumption, especially where space is at a premium, but for homes with more than one bathroom it is generally worth considering stored hot water by means of a cylinder.

Kitchen and Bathroom mixers do not require as high pressures as showers, and as such, do not often need to be pump assisted. If you have a low flow-rate in a mixer tap, Hansgrohe provide a facillity to specify that a product is to be used in a low pressure situation


Gas Safety Certificates by Central Gas Safety ltd