Central Heating Explained

There are three main types of household heating and water systems these days. As a brief guide only, these systems are described in the following sections.

GRAVITY FED SYSTEM


In a gravity fed system water is heated by your boiler. This water is then pumped to your radiators for central heating and/or your hot water storage cylinder, where the water stored is in turn heated.
Water may be supplied to the boiler's heating circuit from a small Feed and Expansion tank often situated in the loft. This tank ensures the system is kept topped up and allows for any expansion or evaporation that may occur.
Alternatively, a System Boiler may be used which has no need of a separate expansion tank.
The hot water cylinder is supplied from another larger tank often situated in the loft. As you open a hot tap, water drawn from the cylinder is replenished by this tank.
Water is supplied to the loft tank/s by the rising main, usually through a ball cock valve and are themselves replenished when levels drop.
Because the tank/s in the loft are isolated from the main supply by a valve, they use only their height to force water down by means of gravity. The pressure at your hot tap is proportional to the distance of the tank above the outlet.

ADVANTAGES: Suitable for addition of power shower pump to provide exceptional flow rates.
DISADVANTAGES: Uneconomical for space. An unpumped system may offer low pressure at taps.
ECONOMY: Water must be heated and stored whether or not it's used.
SYSTEM REQUIREMENTS: Boiler, hot water cylinder, loft tank, rads


COMBINATION BOILERS

A Combination Boiler typically requires no storage tanks. It provides hot water to your taps 'on demand' and/or heat for your radiators as programmed. Combi's only heat what you require.
Offering the advantage of space saving, Combi Boilers are popular.
They can however have the disadvantage of lower hot water flow rates - more often noticed when filling a bath or when simultaneous supply is called for at more than one outlet.
Not particularly suitable for properties with more than one bathroom or shower.
Boilers with bigger and better flow rates are being achieved but performance is still a little lacking.

ADVANTAGES: Compact unit requiring no external tanks - good for space saving. Perform well with showers. Endless amounts of hot water on demand.
DISADVANTAGES: Typically lower flow rates than other systems. Baths can take a long time to fill. Will not support simultaneous demand from several outlets. You cannot install a shower pump.
ECONOMY: You only heat what you need.

SYSTEM REQUIREMENTS: Combination boiler, rads


MAINS OR HIGH PRESSURE SYSTEMS

These are regarded by some as the best, but beware - there are disadvantages here too.
The term typically refers to the pressure you achieve at your hot taps. Mains pressure systems provide mains pressure hot water.
This is only an advantage if you enjoy good mains pressure within your property. If your supply pressure and flow rate are poor there is little point.
There are different system types that can offer this facility and you are recommended to examine them carefully before you decide which is best for you.
Remember, hot water at high pressure can present a risk. Some systems require notification to building control, certified installation and commissioning, and annual servicing to ensure they continue to function safely. A system storing hot water under pressure that is incorrectly installed or poorly serviced can be dangerous.

ADVANTAGES: Hot water at mains pressure throughout your property. Potentially high flow rates. No feed or expansion tanks in loft.
DISADVANTAGES: Slightly more costly to install. Some HP Systems require certification and annual maintenance for reasons of safety. Pressure and flow only as good as your incoming main. You may not install a shower pump on a mains-fed system.
ECONOMY: Choosing a system type requiring annual maintenance will lock you into long term cost. Water must be heated and stored regardless of use.
SYSTEM REQUIREMENTS: Boiler, Pressure Vessel or Thermal Store, Rads.


If you have any doubts you should discuss your installation in detail with your supplier, or your installer who must be CORGI registered. In the case of oil boilers this should be done by an OFTEC registered engineer.

TYPES OF FUEL

Natural Gas - This is piped to your home via a supply company. If you require natural gas and it has not been connected to your home yet then it can cost a lot of money to get connected. You can install a gas central heating system yourself but will need a Corgi registered installer to make the connection to the gas supply. Natural gas is very convenient and there are a good variety of heating systems that can be powered by gas, such as Combi's, back boilers, wall heaters etc. Another benefit is that you will not run out of fuel for your heating.

LPG - This is an alternative to natural gas where it is too expensive or impractical to get natural gas. LPG is supplied to your home via large orange cylinders that stand about 4 feet tall, you usually require two of these cylinders to be fitted with a valve to switch between the two as there are no gauges on them to tell you how full they are. LPG works in exactly the same way as natural gas but you will need a boiler that can be made compatible via a conversion kit.

Oil - Oil fuels some of the most efficient boilers available, the choice of heating systems are fewer than with gas being restricted to just boilers. In most cases to run an oil boiler you will need a tank to be installed outside your house, these are usually large and very hard to disguise, you also have to conform to a variety of regulations in sighting it. Another thing with oil is that if you let it run out then you will need a heating engineer to re-prime the system before you can get it working again.


Solid Fuel - Solid fuel heating boilers are mostly limited to back boilers, or kitchen ranges. There are some solid fuel boilers which run the same way as other fuelled boilers and use automatically fed pellets from a hopper situated outside the house. Most solid fuel heating systems are inefficient as they consist of open fires; they also can be messy and require cleaning out once a day at least.
Solid fuel comes in a variety of forms, coal, wood, etc.

Electricity - Until recently effective Electric central heating was limited to storage heaters or blown air systems. These were both run off cheap rate electricity supplied in the small hours, and in some cases for a short top up period in the afternoon. Though storage heaters (the most popular) are reasonably efficient they have a problem of being on all the time, so if you have a hot day after a cold day in the winter, you will have heating even though you don't need it. They are also susceptible to drafts which can discharge them very quickly indeed.
A new form of electric powered heating has appeared recently in the form of electric heating boilers. These can directly replace other boilers in conventional heating systems; they are very compact, light and can be run off cheap rate electricity. Another benefit is that they are completely silent.


Sources: www.gasapplianceguide.co.uk
www.diydoctor.org.uk