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Central Heating Explained

There is no such thing as a standard central heating system – you can tailor the system to suit your needs.  If working correctly, a central heating system should look after itself with regard to automatically turning itself on and off.  It should use no more fuel than necessary and always keep your house at the correct temperature.  It should also provide all the hot water you need, when you need it.  In a central system, heat is produced from a single source – usually a boiler – and distributed throughout the house, in the form of hot water or warm air.

Energy Efficiency
As a simple guide to efficiency, a scheme has been created with SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK). Efficiency bands have been assigned to products on an ‘A’ to ‘G’ scale.

Loft Insulation & Space Blankets
Don’t forget, insulating your loft or using space blankets is not only energy efficient but will help keep your heat in your home. Look out for the ‘Energy Efficiency Recommended’ logo.  You’ll find it on the most energy efficient products available.  For more information call the Energy Saving Trust Advice Centre on: 0800 512012.

Safety First
Gas is a safe and economical fuel when used correctly.  However, improper installation and maintenance of appliances can be dangerous.  Approximately 30 people a year die in the UK and many more are injured as a result of carbon monoxide poisoning due to faulty gas appliances. It’s illegal for non – Corgi registered installers to carry out gas work in the UK. For your personal safety and protection of your home please make sure you use a registered Corgi installer for all your gas work.  Before allowing anyone into your property to carry out gas-related work insist that you see their Corgi ID card.  The card displays a photograph of the operative, their name, the trading title of the business, an expiry date and on the reverse, details of the different types of gas works the installer is qualified to carry out.  Gas-related work is covered by strict regulations that say you must be competent to carry out the work. Do not attempt to carry out yourself, you could be breaking the law and risking the safety of your family,  plus enforcement action could be taken against you even if the work was carried out in your own home.  To find a local installer in your area you can call 0270 4012300 or visit the Corgi website trustcorgi or look in your Yellow Pages or Thomson Directory.

Understanding Central Heating
The main components used within central heating systems are:
Boiler- A boiler can use natural gas, liquid petroleum (LPG), fuel oil or electricity to heat the circulating water.
Pump- This is used to circulate the water around the central heating system.  In some cases pumps are not needed, as gravity will allow the water to circulate.  Gravity fed systems may still exist in older properties, when these systems are replaced a new boiler type is fitted, commonly a combination boiler.

Pipework- Copper or plastic pipes are used to circulate the heated water.
Radiators- Transfer the heat from the hot water to the rooms.
Hot water cylinder- Hot water passes through the cylinder heating up the stored water.
Cold water, feed and expansion tanks- Provide water for the heating system and the domestic hot water cylinder whilst at the same time acting as a reservoir for any overflow as a result of expansion.
Control or motorised valves- are used to control the flow of heated and cooled water. They open and close the pipework automatically. The power to supply the valves is regulated by thermostats or a time clock.
Programmer or timer- This controls the operating time of the boiler. These controls can be single-channel (timer) to switch central heating on and off or two-channel (programmer) to switch central heating and hot water on and off.
Thermostats- All boilers and heating systems use thermostats to prevent overheating. They also control the temperature of the circulating water.  Thermostats are fitted to hot water cylinders, boilers, radiators and in rooms.
Thermostatic radiator valves (TRVs)- As well as thermostats you can use TRVs to control the temperature in individual rooms.

There are two main types of central heating systems. A wet system, which works by circulating hot water through a network of pipes, and a dry system, in which warm air is blown through a series of ducts. Within wet systems there are four main configurations:

Combination boiler heating system
Combi boilers are now the most commonly used in central heating systems. These run on mains pressure water, thus do not require tanks to be placed in the loft. They also eliminate the need for a hot water cylinder as they instantly heat the water when it is needed. Another benefit of the combi is that, due to it running from the mains water supply, you can create an effective power shower without the need for a pump. Combi boilers require the least amount of plumbing thus offer a cost saving when installing.

Two pipe system
Most modern layouts have a two pipe layout, where hot water is carried from the pump to the inlet valve of each radiator by a flow pipe, which terminates at the last radiator on the circuit. A second pipe, the return pipe, collects the cooled water from the radiators and carries it back to the boiler to be reheated. Although it requires more pipework, this system transmits heat quickly and directly to all radiators in the circuit, raising them all to the same temperature. Just like the one pipe system it’s often described as a vented system.  Older properties may have a one pipe system, but these are no longer installed.

Sealed system
As the name implies, the system is closed, no water tanks are needed and the hot water is supplied direct from the mains. For this system it is most common that the expansion vessel, pressure gauge and safety valve are all integral components within the system boiler. This approach requires less pipework and no separate feed and expansion tank is required for the heating circuit. It’s also possible to introduce an unvented domestic hot water cylinder which also requires no separate feed and expansion tank. Through this method all tanks may be removed from the roof space thereby allowing it to be used more effectively. Unvented domestic hot water cylinders also have the advantage of delivering mains pressure hot water to your taps.

Microbore or small bore system
Microbore pipes are used on two types of system. The microbore pipe takes less water, but can block up, especially in hard water areas.  They are used to feed the radiators from centrally placed manifolds. This system uses 10mm or 18mm copper or plastic pipe. The size of pipe will depend on the radiator size but 10mm is the most common. The high restriction of water flow in these systems can also cause more wear and tear to the pump and boiler.
An automatic bypass must be fitted to all central heating installations.