Central Heating: Planning your Choice of System

Central, or comfort, heating is not a new thing. The Romans used a form of ducted heating, maintained by a team of slaves, stoking-wood furnaces.

Heating has made enormous technical strides in the last few decades, and is now reasonably within the range of most pockets.

In fact, good central heating, backed, of course, by efficient thermal insulation, should give greater all-round comfort, at lower cost, than a battery of individual appliances or open fires.

Modern heating utilizes a range of fuels efficiently, and scientifically directs heat where it is wanted to the best advantage. Central heating is so called because the source of heat is from one point-though the heat is directed around the home. In one or two cases, central heating is provided by warm-air units which emit heat from a central position and circulate this through wall ducts into each room. However, this may also spread stale air and cooking smells.

Which system?

There is a wide choice of heating appliances-gas, oil, solid fuel or electricity. Radiators, or other heat-emitting units, also offer a wide choice.

Heating systems are either ‘wet’ or ‘dry’. The wet system, the most common, derives heat from heated water circulated along pipes from a boiler to various heat exchangers-panel radiators, skirting or fan convectors or ducts. The water finally returns to the boiler along return pipework, where it is reheated and recycled.

In modern smallbore and microbore systems-the term relates to the pipe sizing-a pump is used to accelerate the water flow.

Modern heating systems also allow the provision of domestic hot water, called the ‘primary’ circuit. In some designs, hot water is pumped for the primary. In other cases, ‘gravity’, or natural circulation, is set up by the expansion of hot water.

The microbore principle, which has many technical and physical advantages and may give lower running costs, in some respects is an extension of the smallbore system.

Many early piped heating systems relied totally on the effect of gravity circulation by using large bore pipes; this was neither economic nor efficient.

Open smallbore and microbore systems utilize a feed-and-expansion cistern, located at a high point, such as the loft. This provides for the thermal expansion of hot water, which discharges into this cistern if the water reaches a high temperature.

Evaporation loss is also made up from this cistern, which is simply a smaller version of a cold storage cistern, fitted with a ball valve to regulate the supply of water.

Sealed systems are completely isolated from atmosphere and are pressurized and able to operate at much higher operating temperatures than open systems.

Another arrangement is the loop system, providing a form of heating ‘ring main’. Loop systems are a development found largely with linear heaters (skirting convectors). Installing these can cut down dislocation to house fabric. The skirting radiator is part of a continuous smallbore pipework loop. Power convectors may usually be used on loop systems.

The first smallbore heating systems utilized a single pipe. Pipes were run along the skirting boards, to avoid lifting floorboards. This did not always present the most attractive appearance aesthetically. The grave disadvantage of this arrangement is that water temperature falls as heat is transmitted, and further along the system the size of radiators have to be increased to give the desired heat output.

Smallbore and microbore systems utilize separate flow and return circuits. Enabling an even temperature of flow water to be maintained.


Electrical systems are normally ‘dry’, though there are electric storage systems which heat hot water and circulate this around pipework.

The most common form is the storage unit. This runs off cheap electricity, stored at night, which heats up refractory blocks, with electric elements.

These are, in effect, electrical radiators, which emit the stored heat throughout the day and can be switched over to full-price electricity by day if a boost is needed. Some are fan-assisted to give a higher heat output. Such systems do not, however, provide instantaneous heat.

Ducted systems can be operated by any kind of heating source. The heat exchange is effected by air circulating and fan assisted through an electrically heated element, or through grills with circulating hot water. Ducts or ‘registers’ of appropriate sizes are placed to provide the de-sired comfort levels.

Ducted systems, with few exceptions, are installed during house building because of the trunking or ducting needed to circulate the warm air.

10. November 2011 by admin
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