Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Correct Pitch for Two-Pipe Air Vent System

PetePete Member Posts: 6
for the advice provided. I had bought Dan Holohan's Pocketful of Steam Troubleshooter. It was very useful addition to my library but it didn't really address the two-pipe air vent systems. Thanks for filling in the gaps.



  • PetePete Member Posts: 6
    Correct Pitch for Two-Pipe Air Vent System

    I have old house in Boston that is heated with radiators that use the two-pipe air vent system (no steam traps, two pipes attached to the bottom of the steam radiator with air vent near top).

    Was the optimum pitch for these radiators? Pitch towards the bigger input pipe or pitch towards the air vent end?

    Also I am insulating all the bare steam pipes in my basement. I found white pre-slit fiberglass pipe covers (3 ft in length) in Home Depot that range from $4.50 to $5.29 each in price. Could this price be bettered much if I found a wholesaler or factory outlet? Anyone know of any in the Boston area?



  • ta finneganta finnegan Member Posts: 121
    Pipe pitch

    Pitch sometimes is a matter of trial and error, but in general, in two-pipe, steam comes in one and condensate out the other. So pitch toward the condensate.

    Two-pipe with vents eh? Sounds like an old vapor/vacuum that has been through a number of "cosmetic surgeries".

    If you have pictures, that would be great to see.

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
  • two pipe air vent IS the name of it

    It pre-dates vapor. It is an improvment on one pipe that allows adjusting the heat with the radiator valves.

  • PetePete Member Posts: 6

    Here's a picture that I dregged up. It doesn't show much. I will to take a fresh one if anyone thinks it will help much.

    I think my 1880 house uses a steam system that existed after one-pipe systems but before the more conventional two-pipe, steam trap systems bacame popular.

    I can't get much information on how to optimize my 'hybrid' system. Any rules-of-thumbs would be gratefully received.


  • SteamheadSteamhead Member Posts: 11,381

    it's two-pipe, air-vent all right. Is that an American Rococo radiator? Those look fantastic when cleaned up and repainted- just ask Mad Dog!

    To answer your questions- the rad should pitch slightly toward the return end. In this system the steam lines were not sized to handle counter-flowing radiator condensate.

    Your steam mains should have vents at their ends. These should be sized to vent all the air in the main in a minute's time. Then each radiator takeoff has equal access to the steam.

    Do not install a vent on the return lines. On this system, the returns only handle condensate- not air as you'd find in a Vapor system.

    All your steam pipes should be insulated with fiberglass pipe insulation at least 1-inch thick. You won't find this stuff at Home Depot, but a local supply house would carry it or know where to get it.

    Keep the pressure LOW. If you have a Pressuretrol, set it to stop the burner (cut-out) at 1-1/2 pounds and restart (cut-in) at 1/2 pound. If you have a Vaporstat, set it to cut out at about 12 ounces and in at 6.

    When you've done all this, sit back end enjoy your classic, efficient heating system.
    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
    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.
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!