Richard Trethewey points out a radiator's risers
Photo: Russell Kaye
Q: I'd like to remove one section of a cast-iron radiator to make it shorter. How would I go about it?
James Conbeer, Coal Township, PA.

A: Richard Trethewey replies: If you shorten the radiator, it won't give off as much heat. And even if you don't mind the loss of heat, you might still want to leave it the way it is because disassembling one is either a big job or nearly impossible, depending on the type of radiator you have.

The first step—disconnecting the radiator from its risers—is the easy part. Hot-water radiators always have two riser-pipe connections, while steam radiators usually have one but sometimes have two. If you have hot-water radiators, you'll have to drain the system first. Disconnect the radiator from its valve using two plumber's wrenches, one to turn the nut, the other to apply pressure in the opposite direction to avoid cracking the valve. Now comes the difficult part.

In radiators built before 1930 or so, the sections were connected top and bottom with nipples, 1¼-inch-diameter pipes threaded at both ends. You'll be able to see the lugs inside the nipple if you peer in the end of a radiator with a flashlight. Over the years, those threads corrode, making the nipples almost impossible to remove. A good soaking in Liquid Wrench and some heroic turns with a radiator spud wrench—a steel bar with facets to engage the lugs—might crack them loose, if you're lucky, but I'd leave that type of radiator alone if I were you.

Newer radiators were assembled with push nipples, short lengths of smooth pipe that form a tight seal when the radiator sections are pulled together. Cut the connecting rods that run the length of the radiator and pry the sections apart by tapping a splitting wedge between them. Work slowly; you could crack a section if you're not careful. Once you've taken off the sections you want to remove, clamp a Vise-Grip on the exposed nipples and pound them out. Get new push nipples from a boiler specialist like Oneida County Boilerworks (Online Boiler). Joel Minnich of Radical Radiator Restorations heats them with a torch until they're red hot. After loosely reassembling the pieces, he pounds the sections back together with a sledgehammer, cushioning the blows with a block of lead.

Finally, you'll have to reposition or extend the risers to account for the radiators shorter length. All in all, it's probably easier to buy a new or salvaged radiator of the size you want.
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