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Questions on adding main vents to old steam system

I just got the great E.D.R. book by Dan Holohan, and was happy to find that the Dunkirk PVSB-5D replacement boiler we put in a few years ago (when the old boiler leaked and snuffed out the gas burner!) happens to be just right for the radiator square footage. But I also read in Dan's Lost Art book that it's all about the venting, and we don't have any main vents on our pipes.

We did replace all the radiator vents with much faster Gorton valves when we got the new boiler, which was a big improvement. But it still takes 10 or 20 minutes when it cycles to get heat at the last radiators.

So I'd like to know the likely cost and payback for installing 1 or 2 main vents. Here are the details:

Front main: 20 ft 2-in iron pipe, asbestos "insulation," serving 251 sq-ft of radiators.
Rear main: 12 ft 1-1/2 in pipe, asbestos, for 100 sq-ft.

Here's the end of the front main:

Here's the rear main:

If you think this is worth doing, here are my questions:

1. Am I right to think the valves should be back 15" past the elbow on the LOWER return, on a 6'' to 10" nipple, since the elbow is only a few inches from the last risers for both mains, on the upper (supply)?
2. What size, model, etc., valves are recommended for each?
3. How much asbestos should be removed to allow a contractor to splice in the fittings?
4. Any steam heat contractors recommended near me here, in the Albany, NY, Capital District?

Thanks - Any help & suggestions are sure appreciated!


Mad Dog_2


  • ethicalpaul
    ethicalpaul Member Posts: 5,704
    edited April 5
    No one is responding, so I will:

    1. It doesn't matter much honestly. Anywhere around the end of your mains is fine. There is this idea that there is a "slug of water" that slams down the main when steam starts to be produced. This is a myth so just put the vent somewhere. Raising it a little above the main is fine if you have room. It doesn't hurt.
    2. Your mains are quite short and obviously insulated. I would put a Gorton or Maid O Mist #1 (they are basically the same) on each one.
    3. If there's not a reducing tee or other handy fitting hiding at the end of your mains, then I'd have a couple feet of asbestos removed from the end of each main, and then drill and tap a 1/4" NPT hole in the top of each pipe
    4. Try https://heatinghelp.com/find-a-contractor/

    Is it worth doing? Hard to say. I'd say it depends completely on how much it will cost to touch that asbestos. 10 to 20 minutes from start of call for heat to receiving steam at your radiators doesn't sound bad. Is it 10 or is it 20?

    Also it depends greatly on how much time has passed since the last call for heat. A main has to be heated to steam-hot in order to let the steam pass, regardless of venting and that takes time.

    To get a better idea of the actual time your system takes to clear the air out, have it do a call for heat just a few minutes after a call for heat ends and all the radiators are nice and hot. Remove a vent from your closest radiator and see how long it takes for the steam to appear there. Even that can be misleading since your radiator, no matter how hot it is, will still condense steam so you might not see it come out until some time after steam has reached it.

    It's just a lot easier to time this with an existing main vent which you don't have of course.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Long Beach Ed
    Long Beach Ed Member Posts: 1,209
    edited April 9
    Just as Ethical references, many of the recommendations we know and read are "proper piping practices". When in the field, an experienced workman can deviate from these practices if he knows performance will not be affected, or when the cost/benefit isn't favorable.

    In a small system, depending on its specific design the cost of adding main vents to a difficult configuration may not improve the performance or efficiency enough to justify the work. (if the system permits sufficient radiator venting). As mentioned above, you can get an idea of system improvement by taking some timing measurements with and without a radiator vent removed from a radiator close to the end of the main.

    While well-vented mains can offer a vast improvement to most systems, don't simply assume that adding main vents will be a worthwhile investment where complexities such as asbestos remediation are necessary.

    The most valuable time spent on this job is in the testing and research you do before picking up a tool.

  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,004
    @ethicalpaul said, "drill and tap a 1/4" NPT hole in the top of each pipe"

    I assume this suggests the vent be threaded directly onto the main or a fitting or two be added then the vent.

    My question is, "Does tapping the main meet code?" I'm not a student of the codes, so I don't know. I also recognize the temperature and pressure, under normal circumstances are pretty low.

    Maybe a saddle tee with an appropriately temperature, pressure and steam rated gasket is allowed.

  • Gordo
    Gordo Member Posts: 857
    Steamhead shows us how he taps a cast iron tee for a Gorton #2 main vent.

    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
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