How it works: One-pipe steam

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One-pipe steam radiator.
Single, large valve at the bottom of the radiator, air vent midway up.


In one-pipe steam installations, steam flows from the boiler to the radiators, and water flows back again through the same single pipe. One-pipe radiators are easy to identify because they have just one pipe connected to them, always at the bottom, and an air vent attached to one side, usually about halfway up the height of the radiator.

This is different to two pipe steam installations in which the steam flows from the boiler to the radiators in one pipe, and water returns to the boiler through a separate, second, pipe.

Read an introduction to two-pipe steam systems here.

Steam is lighter than air, and it’s hot – to state the obvious – so its natural buoyancy causes it to rush upwards out of the boiler and towards the radiators.

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