How Radiators Work

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Image published in Audel's House Heating Guide, 1948. Image used by permission of copyright holder.

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Image published in Audel's House Heating Guide, 1948. Image used by permission of copyright holder.

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Image published in Audel's House Heating Guide, 1948. Image used by permission of copyright holder.

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This valve from a Joy radiator in Titusville is an example of the previous diagram.

Cast iron radiators appeared in Europe in the mid nineteenth century. They became an important part of the heating and manufacturing landscape in America shortly after. Individual radiators are connected by pipe to the heating mechanism, usually a boiler that might be coal, gas, oil, or even wood fueled. Hot water systems circulate water warm to about 180 degrees through a series of pipes connected to both ends of a radiator. The water goes in one pipe and out the others. The radiators warm and radiate heat to the walls and room.

Radiator heat is even and steady. Steam radiators work on a one-pipe or two-pipe system. In the earlier, one-pipe system, steam from the boiler pushes cold air out vents on the steam mains and on each radiator. Steam vents require upkeep, with modern replacements easy to install for the homeowner. Steam vents on the main were more intricate with a grill that required cleaning, so these may have been removed from older systems, cutting down on efficiency, as the cold air then had more piping to travel to be expelled from the radiators.

In one-pipe systems, the steam enters and exits the radiator through the same pipe. The steam vents close after all cold air is expelled and the hot radiators send out heat to the walls and room. When the temperature of the steam falls, the steam condenses and returns via gravity through the original pipes.

With a two-pipe system, the condensate would return through a second pipe. Residential steam systems run on almost no pressure – ideally at .5 PSI, with a cutoff of 2 PSI, whereas commercial steam systems operate at high pressure. A temperature of 212 degrees Fahrenheit must be attained to create steam, so radiators can heat up so much, they are dangerous to touch and can burn. Radiator covers are often used to protect against steam burns, though steam radiators are also used without them.

T. C. Joy’s company created both hot water and steam cast iron radiators. He developed new shapes and designs in the piping of the radiators themselves, in order to increase the output of heat. T. C. Joy patented these designs and more innovations, directly related to the heating industry.