Radiators are heat exchanging devices and are one of the oldest and most effective ways of heating buildings. Typically they consist of hollow metal panels through which hot water is pumped. Convector fins may be welded to the panels to increase their effective surface area, allowing more air to come into contact with the metal. According to British Standards, radiators should be placed on external walls, wherever possible under windows. This is because mounting is easier on external walls and these are usually the coldest parts of a room.
Radiators use the heat from hot water or sometimes steam to warm the surrounding air. The advantage of using steam is that it can flow through pipes under its own pressure without needing pumps. This is useful for large and tall buildings, however, steam is less efficient due to the higher temperatures at which steam systems operate.
Water hammer is a banging sound that can be made by steam pipes and radiators. It is due to some of the steam condensing into water in a horizontal section of the steam piping and pushing the water at high velocity into a pipe fitting.
 Types of radiator
 Panel radiator
These can be either single or double panels without convector fins, and now largely outdated. The panel refers to the long metal containers that run parallel to the wall. The longer the panel, the larger the heat-emitting surface area, so bigger radiators will emit more heat. A double panel radiator will emit more heat than a single panel radiator of the same length.
 Convector radiator
These are similar to panel radiators but have convector fins welded to them. The three different types are:
- Single panel single convector: One front steel panel and one convector fin.
- Double panel single convector: Two steel panels (front and back) and one convector fin.
- Double panel double convector: Two steel panels (front and back) and two convector fins.
Round top radiators allow the convector fins to be seen, whereas compact radiators include a grill across the top of the panels to obscure the view of the fins (see top image).
Column radiators are made up of steel tubular columns welded to end pieces at the top and bottom. Column radiators can range from single to four columns in depth. Column radiators are popular for their more traditional appearance.
 LST radiator
An LST radiator has an efficient internal heat emitter in a robust steel enclosure to ensure safety and concealment of pipework and valves. This type of radiator is often found in places where safety concerns are important, such as hospitals, nurseries, schools, care homes, and so on. They do not have sharp corners and maintain a low, safe-to-touch surface temperature, while at the same time delivering the required heat output.
 Skirting board radiator
This type of radiator is placed inside a skirting board, saving the wall space. Hot water is piped through the system from the central heating system.
Bleeding a radiator involves venting air that can build up over time, preventing proper operation of the radiator.
Radiators should be bled regularly to ensure the efficiency of the central heating system. It is possible to check whether bleeding is necessary by checking for cool spots, especially near the top of the radiator. Bleeding can be done using a bleeding key or flat-heated screwdriver to open a valve at one end of the radiator. This allows the release of the trapped air until liquid starts to escape, at which point the valve should be quickly closed.
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