Sizing Radiators For Home Central Heating Systems

Before you start sizing any type of radiator it is essential to decide which type to use and where you are going to install them.


The best place to put radiators is under windows where the downward currents of cold air will be heated, so giving the room an even temperature. This will also prevent wall stains above the emitters.

If you have to place the radiator against a wall, these stains can be prevented by fixing a shelf above it.

Types of domestic radiators

Panel radiators are made of light steel pressings welded together. They are reasonably attractive and cheap to buy. They present a large surface area. Single and double versions are commonly available in a variety of heights and lengths.

Although called radiators they radiate very little heat, working mainly by convection currents. They are easy to install and can be hung on light partitioning from brackets supplied with the radiators.

Their main disadvantage is that they are prone to attack by corrosion. To overcome this an inhibitor can be put into the system. This is usually a liquid (Fernox) which is put into the F & E tank.

There are many types of panel radiator on the market. When sizing always read the maker’s instructions. Lockshield valves (lsv) and wheel head (wh) valves are fitted to either end.

Convector radiators are outwardly similar in appearance to panel radiators and are fitted with steel fins on the reverse face (or between the two panels of a double radiator) which greatly increase the surface area and thus the heat output. A double convector radiator may have a heat output up to 40% greater than the same size of panel radiator, and they are therefore more economical in terms of wall space. Fitting is as for panel radiators.

Fan convectors provide instant controlled heat. A fan capable of low, medium and boost output blows air over a finned heat exchanger. It can also be used in summer to give a cold air blow.

Fan convectors are small and efficient but the units themselves are expensive. Individual control is very easy because the heat output is governed by the fan which can be switched and thermostatically controlled. Installation is simple since there is only a flow and return water pipe. The only drawback is that you also need an electric socket outlet next to each unit. The fans can be noisy and need regular maintenance if they are to give good service.

Skirting heaters

These provide a neat and unobtrusive system. A skirting heater is a form of convector and special enclosures are available shaped to take the place of a skirting board. The drawback with this system is that it may be difficult to make connections around doorways: also it may not provide enough heat in large rooms.

The position of the radiators or fan convectors can now be drawn on the sketch plan together with the boiler, hot water cylindei and the feed and expansion (F & E) tank The sketch plan can be used equally well for both small and microbore systems.

At this stage you can decide on the type of controls you wish to install, whether to use small or microbore piping, and a pumped or gravity-driven system. All this will affect the positioning and design of your pipe runs to the individual units.