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Technical Help for Heating and Hot Water Systems

Technical information explaining the different type of hot water and heating systems, and how to tell which type you have.

Combination boilers

Combination boilers have the ability to heat hot water on demand and run central heating systems, this system provides hot water at mains pressure. A combination boiler occupies a small amount of space, so is ideal for small flats and houses, as there is no need for water tanks and hot water cylinders, as in other systems, such as Gravity Systems, Unvented / Pressurised Systems & Pumped Systems.

Advantages
Never runs out of hot water.
Hot water delivered at mains pressure
Ideal for small buildings, as they occupy less space

Disadvantage
Should the boiler ever fail both hot water and heating are lost
Not so suited for supplying multiple hot water outlets at once

Do I have this system?
If you do not have any tanks in the loft or an airing cupboard, then you most likely have a combination boiler.

Gravity Systems

Gravity System this system consists of a boiler, hot water cylinder, and cold water tank. The hot water cylinder holds the hot water (usually in an airing cupboard) and the pressure to drive the hot water is generated buy the cold water tank in the loft. It is the height of this tank that determines the pressure of the hot water.

Advantages
Better suited to multiple users/outlets

Disadvantages
Once the hot water tank is empty it can take a long time to reheat
Hot water pressure can be low.

Do I have this system?
If you have a tank in the loft and an airing cupboard containing a hot water cylinder and a boiler, then you most likely have a gravity system.

Pumped Systems

Pumped Systems this essentially of the same design as a gravity system but a pump is fitted to boost the hot water pressures. The pump may be just for one outlet (shower) or a 'whole house pump' which provide pressurised hot water at all outlets.

Advantages
High hot water pressure
Well suited to multiple user/outlets

Disadvantage
Uses available hot water up very quickly
Once the hot water tank is empty it can take a long time to reheat

Do I have this system?
If you have a tank in the loft and an airing cupboard containing a hot water cylinder, a boiler, and a pump that runs when the hot water is turned on, then you most likely have a pumped system.

Unvented/Pressurised Systems

Unvented/Pressurised Systems these systems use a large water cylinder that is pressurised using the mains water, the cylinder can be heated by a combination boiler, conventional boiler or electricity.

Advantages
Hot water at mains pressure
Well suited to multiple user/outlets
Larger tank use than in a gravity system

Disadvantage
Tanks tend to be very large and take up a lot of space
Once the hot water tank is empty it takes a long time to reheat

Do I have this system?
If you have a hot water cylinder usually white in colour, a boiler, but no tank in the loft, then you most likely have a Unvented/Pressurised

Water Pressures

Bar This is a measure of pressure. A water tank one meter above the shower head would generate a pressure of 0.1 Bar.

Mains Pressure This is the pressure that water enters the house. The legal minimum pressure water companies must maintain is 0.7 Bar or 7 metres of static head.

Disclaimer

This information is given as a guide only, if in any doubt please consult a qualified tradesman. SMR accepts no liability for the accuracy of the information given.
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