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Old radiator vents smaller than 1/8"?

I have an old 5-tube, 14-section Weil-McLain radiator in our rental apartment that I *think* is a Cameo model. It's connected to a steam heating system. Our new tenant just turned on the heat for the first time this season, and she noticed that there isn't any vent valve on the side of the radiator -- just a hole -- and so it's turning her living room into a steam room.

Here's the odd thing. All of the other radiators in her apartment and in ours have vent holes that accept a standard 1/8" vent, but this hole is smaller -- between 1/16" and 3/32". I didn't have much luck searching online for replacement vents in that size -- it doesn't seem like anything smaller than 1/8" is available out there. Is there any way to figure out what type of vent fits this radiator hole? Or is searching for replacement vents a fool's errand, and should we be doing something else, like fitting an adaptor to this hole so it can accept vents of a more standard size?

Thanks in advance for the help. I searched through the forum quite a bit before posting, and the threads provided a great crash course in steam heating.


  • FredFred Member Posts: 8,418
    Your best bet is to tap that hole out to accept a standard 1/8" vent. It is a very simple task if you have a tap or purchase one. Very inexpensive too.
  • SteamheadSteamhead Member Posts: 13,768
    Agreed. From the looks of it, part of an old vent broke off in there. Be very careful as you drill and tap.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • I believe the drill size will be stamped on the tap.
    In a situation like this, I would drill first using a firm hand on the drill, as the thin amount of metal of the original vent will probably become wrapped around the drill bit, as you break through.
    After drilling, when tapping, rotate the tap to the left until you can feel the threads drop into alignment, and then proceed in the standard clockwise direction. Turn the tap 90 degrees, and then back up 45 degrees, in steps, until you have cut enough thread, so the swarf gets pushed out of the way.
    Don't run the boiler too long with the inlet valve shut or the boiler may lose water, as a tiny wisp of steam may still make it through the valve, and be unable to drain out again.--NBC
  • LionA29LionA29 Member Posts: 254
    @RhodyGuy try cleaning the surface areas and take a good look at it. It's an easy fix and can be inexpensive as @Fred suggested.
    I agree with @Steamhead, the valve nipple is probably in there
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,940
    I agree the old vent broke off in the hole. Drill it carefully and re-tap the hole and you should be fine.

    They do make a 1/16 pipe tap but cant get fittings for it anyhow
  • RhodyGuyRhodyGuy Member Posts: 2
    Thanks for the helpful feedback, everyone. I'll try the drilling and retapping tomorrow.
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