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How do I tap this water rad for a steam vent?

My customer wants to put this radiator in her kitchen as a replacement for a larger one that was removed to gain floor space. This one will go about 8 feet away from the old one's location. My question is about the steam vent. There is no tapping now as this rad was in a hot water system. In the picture you can see there is a spot in the end casting that looks to be where the mtg'er could have tapped it for a steam vent. Can I just drill this out and tap it for 1/8th inch pipe and screw in a steam vent?


  • Jamie Hall
    Jamie Hall Member Posts: 19,420
    Should work. Be gentle. Cast iron cracks if you look at it cross-eyed...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • You’re talking about the lower boss, I hope as the upper one is for a hot water vent.—NBC
  • bruce_21
    bruce_21 Member Posts: 237
    Yes, the one about 10 inches from the bottom.
  • ChrisJ
    ChrisJ Member Posts: 13,257
    edited September 2018
    My experience has been cast iron drills like butter with a little oil on the bit and low speed with a lot of pressure. Something like 200-300 RPM.

    I'd drill it with a size Q drill bit and then tap it by hand 1/8" NPT.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • luketheplumber
    luketheplumber Member Posts: 147
    what did you do with the old one?
    I just earned my GED and am looking for a apprenticeship with one of these steam gurus on this site!