Radiator (heating)

A cast iron radiator with Single-pipe steam supply

Steam has the advantage of flowing through the pipes under its own pressure without the need for pumping. For this reason, it was adopted earlier, before electric motors and pumps became available. Steam is also far easier to distribute than hot water throughout large, tall buildings like skyscrapers. However, the higher temperatures at which steam systems operate make them inherently less efficient, as unwanted heat loss is inevitably greater.

Steam pipes and radiators are prone to producing banging sounds called steam hammer. The bang is created when some of the steam condenses into water in a horizontal section of the steam piping. Subsequently, steam picks up the water, forms a "slug" and hurls it at high velocity into a pipe fitting, creating a loud hammering noise and greatly stressing the pipe. This condition is usually caused by a poor condensate drainage strategy and is often caused by buildings settling and the resultant pooling of condensate in pipes and radiators that no longer tilt slightly back towards the boiler.

A hot-water radiator consists of a sealed hollow metal container filled with hot water by gravity feed, a pressure pump, or convection. As it gives out heat, the hot water cools and sinks to the bottom of the radiator and is forced out of a pipe at the other end. Anti-hammer devices are often installed to prevent or minimize knocking in hot water radiator pipes.

Unlike steam or hot water systems which receive heat from a boiler, electric radiators produce heat from electricity at the location of the radiator. This heat may be transferred to a fluid (such as oil) inside the radiator. The oil circulates inside the radiator by convection, which distributes the heat from the heating element to the surface of the radiator. Smaller electric radiators have the advantage of being portable, as they do not need to be connected to pipework. Some electric radiators can also use hot water, this is particularity common for heated towel rails, where the radiator uses hot water when the central heating system is running but switches to electricity when heating the whole building is not required.

Cast iron radiators may be used with hot water or steam systems. Traditional cast iron radiators are no longer common in new construction, replaced mostly with forced hot water baseboard or panel radiators, but they remain available.

Hot-water baseboard radiators consist of copper pipes which have aluminium fins to increase their surface area. These conduction boiler systems use conduction to transfer heat from the water into the metal radiators or convectors.

The radiators are designed to heat the air in the room using convection to transfer heat from the radiators to the surrounding air. They do this by drawing cool air in at the bottom, warming the air as it passes over the radiator fins, and discharging the heated air at the top. This sets up convective loops of air movement within a room. If the radiator is blocked either from above or below, this air movement is prevented, and the heater will not work. Baseboard heating systems are sometimes fitted with moveable covers to allow the resident to fine-tune heating by room, much like air registers in a central air system.

Panel radiators are welded from flat or corrugated steel panels, and are usually hung from the wall. They are usually used with hot water systems, but electric versions are also available. The panels often have fins attached, which increases the surface area and therefore the amount of heat that can be transferred into the air. Several panels may be stacked together to make one radiator, and the resulting radiator is referred to with a two-digit type number. The first digit is the number of panels, and the second is the number of sets of fins, for example a type 21 radiator has two panels with one set of fins in between. Air flow around the radiator and between the panels is by convection only, and must be unrestricted if the radiator is to reach it's design performance. The heat output of panel radiators is regulated by controlling the flow of hot water, with either a manual or thermostatic valve.

A fan-assisted radiator contains a heat exchanger fed by hot water from the heating system. A thermostatic switch energises an electric fan which blows air over the heat exchanger to circulate it in a room. Its advantages are small relative size and even distribution of heat. Disadvantages are fan noise and the need for both a source of heat and a separate electrical supply.

In underfloor heating, tubing is placed on the floor throughout the room and later covered with a concrete layer during construction.

Also known as "radiant heat", underfloor heating uses a network of pipes, tubing or heating cables, buried in or attached beneath a floor to allow heat to rise into the room. Best results are achieved with conductive flooring materials such as tile. The large surface area of such room-sized radiators allows them to be kept just a few degrees above desired room temperature, minimizing convection. Underfloor heating is more expensive in new construction than less efficient systems. It also is generally difficult to retrofit into existing buildings.

The Roman hypocaust employed a similar principle of operation.

Skirting-board radiators are a form of heating which involves placing radiators inside a skirting board. Hot water is piped though the system, usually taken directly from the central heating system.[5]