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How to Replace a Steam Radiator

Ask This Old House plumbing and heating expert Richard Trethewey replaces a small radiator with one that’s the correct size


  1. Switch off the steam boiler to prevent risk of scalding.
  2. Loosen the nut holding the radiator. Make sure the wrench is biting the nut in three different corners to prevent the nut from deforming.
  3. Carefully remove the old radiator.
  4. (Optional): To replace the hand valve, use one wrench to bite the pipe and one wrench to bite the valve. Move in opposite directions to loosen. This step may require a pipe for persuasion.
  5. (Optional): To replace the spud, insert the spud wrench to loosen, then remove.
  6. Make all the necessary connections with the wrench: floor to hand valve, hand valve to spud. Apply the pipe dope and the wicking to each thread to ensure a secure connection. The hand valve should be parallel to the floor in order to fit back into the radiator.
  7. Carefully fit the new radiator into place and connect it with pipe dope and the wrench.
  8. Open the hand valve and turn the boiler back on.


Richard used an existing radiator left over in the homeowner’s house, but a replacement radiator could be bought at plumbing supply stores or salvage yards.

The other tools for this project, including the hand valve, pipe wrenches, and a spud wrench can be purchased from a plumbing supply store.