Radiators are often found in older homes, but they remain an efficient home heating system, despite their age. Understanding the parts of a radiator, including its valves, piping system and boiler, can help you accurately control the temperature of every room.
How Home Radiators Work
Home radiators distribute steam or hot water through a series of coiled pipes called fins. The fins are made of cast iron or another material that easily conducts heat. The heat transfers from the steam or water to the cast iron and then transfers to the air around the pipes.
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The air in a room naturally circulates past the radiator without the need for a fan, thanks to the density differences between cold and warm air. As warm air rises away from the radiator, cooler air is pulled from the floor-level alongside the warm radiator.
The steam or water inside the radiator coils cools off as the heat transfers to the air. The resulting cool water is recycled back to the boiler, where it's heated (typically via a gas or oil burner) and redistributed to the radiators. If you've ever noticed that your home's radiators are "crooked," it's actually by design. The radiator in a steam system slopes downward to help the condensate travel back to the boiler via gravity.
Basic Parts of a Boiler
At the heart of a radiator system is a water tank known as a boiler. The water sits in a chamber above a heat source, which is usually a flame powered by a gas or oil burner.
Two or three pipes emanate from the boiler: the pipe sticking out of the top of the boiler transports steam to the radiators, whereas the one closest to the ground carries the condensed, cool water back into the heating chamber. Sometimes, steam and condensate travel along the same pipe. Finally, a large metal pipe leading from the water chamber to the outdoors is known as the exhaust flue or vent, and it carries noxious combustion gases away from your home.
In a hot water radiator system, the water is still heated in a "boiler" but does not actually reach boiling point. Therefore, no steam is generated. The hot water is circulated to the radiator with the help of an electric pump.
Thermostatic Valve on Radiators
When the steam reaches the radiator, it travels through the fins. At the end of the final fin sits a thermostatic vent, which closes in response to the temperature of steam or hot water. This ensures the radiator operates efficiently by keeping the steam inside the fins until the heat successfully transfers to the air. When the steam condenses, the thermostatic vent opens, allowing the liquid to travel back to the boiler through the return pipes, much like taking your thumb off the end of a straw.
Some radiators used in a hot water system feature a manual thermostatic valve, which allows you to control how much hot water flows through the radiator. As the temperature in the room decreases, the thermostatic valve opens, allowing more flow and increasing the temperature.
Other Radiator Valves
Air pockets reduce the efficiency of radiators by allowing less hot water to enter the fins. A bleeding valve allows air to exit the fins in a hot water system. These valves can be manual or automatic and are located near the top of the radiator fins.
Lockshield valves are located at the bottom of the radiator just above the supply pipe. They help make sure each radiator in your home heats up at roughly the same time. Without lockshield valves, the radiators will heat up in succession, with the radiator furthest from the boiler always being the last to warm up.