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Single Steam Pipe Venting - Sizing

How do I properly vent my mains?  I installed 3 Gorton #1's recently and

this really helped me get the radiators to heat at about the same

time.  Does any one have a suggested remedy?  I don't know the proper

venting for my system and the equations or web pages I 've seen are


<a href="http://www.tlv.com/global/TI/calculator/steam-pipe-sizing-for-steam-vent.html">http://www.tlv.com/global/TI/calculator/steam-pipe-sizing-for-steam-vent.html</a>

Please advise if you can. Thanks.


  • how many vents are needed?

    i advocate the addition of enough main vents to enable the system air to escape easily at a back-pressure of 1 ounce, as verified by a good low-pressure gauge, mounted on the same pigtail as the pressuretrol/vaporstat. this would be observed as the water just begins to boil.

    on your drawing, i notice that the main vents do not appear to be much higher than the boiler. this location could become water-logged, as the pressure rises and pushes the return waterline higher than the boiler waterline. a higher connecting point would make sure there is no water preventing the venting.--nbc
  • Boiler Talk
    Boiler Talk Member Posts: 136
    Drawing is not to scale

    I ordered the venting chart.  The picture I attached shows the true situation - not my abs!

    Vents are where they need to be, but I read that the mains should vent first and quick to save money. 
  • crash2009
    crash2009 Member Posts: 1,484
    edited February 2012
    Diagram looks good

      Shows slope and size of main, riser size.  Once you get the venting handbook, you will need to know how much air is in the risers.  It's not much, but it still needs to be counted.  On mine I just estimated, ceiling height plus 4 or 5 feet for zigging and zagging through the floor.  Some of mine had longer runouts than normal so I added a bit more for that.

    Also you will need to know how many EDR each radiator has.  You can't figure the air content without it.  Here is the "How To"
  • Boiler Talk
    Boiler Talk Member Posts: 136
    Venting the Mains

    OK.  My system may not be optimum for pipe sizing.  I heard 1" pipe is not the best, but I have it and it isn't going to change.  The Capacity chart doesn't show 1" pipe, but I guess if I picked .008 CF per 1' of pipe, I couldn't be too far off.  Anyway, I think the main pipes have about .5 CF each and if Gorton #1 can vent .7 CFM at 3 oz's, then I guess I'm OK. 

    Now I will deal with the radiators, but I think I'm OK here as well.  
  • crash2009
    crash2009 Member Posts: 1,484
    One, two, and three ounce scale

    .008/ foot should be pretty close for 1" pipe.  When calculating how many and what size of vents you need, use the 1 oz scale for main vents, the 2 oz scale for risers (if nescesary) and the 3 oz scale for the radiators.  The reason for this is to encourage the steam to fill the mains first, risers second, and of course the radiators last. 
  • Boiler Talk
    Boiler Talk Member Posts: 136
    One last question

    The booklet has a chart about air in pipes.  When it is said 1-1/4" pipe has .010 Cu Feet of air in a linear foot of pipe, is it under pressure?  
  • crash2009
    crash2009 Member Posts: 1,484
    Under pressure

    I don't think so.  I would think that the .010 would be based on atmospheric.  Hope this isn't your last question.  Stick around awhile.  We want to hear about how well things are running once you finish the upgrades.  Have you looked at any brands of radiator vents yet?
  • Boiler Talk
    Boiler Talk Member Posts: 136
    Pipe Volume in booklet

    I think the booklet could be a bit clearer on volumes of the piping.  What is the equation used to measure CF's of pipes?  I went to math sites to find the volume of an inside-diameter 1.25" foot long pipe and come up with .008 instead of .010.  There are additional equations available that include Pressure variables.  Just want to check, ya know?

    No biggy.  I'm guessing the numbers for volume are close enough.  Everything is rounded anyway. 

    So now I have two Gorton #1's on one side and a single on the other main.  The 3 together at 1 ounce are about 1.0 and my total pipe CF is 1.068.  I'm close for the total but Volume on each main is about the same - .584 and .484.  My Rad's heat about the same, but could be better.

    More Later. 
  • Boiler Talk
    Boiler Talk Member Posts: 136
    edited March 2012
    Vented the Mains

    I forgot about your advice on how to use the scale tables, but I ended up doing it that way because I thought I'd just go with the lowest pressure.  I calculated the cubic feet to vent for the risers and the radiators too.


    I now have two Gorton #1's on one main and a Gorton #1 and a Jacobus Maid-O'Mist self adjusting type vent on the other main.  The mains are about the same length, but the shorter one doesn't have any insulation on the return piping.  Thus, that under-insulated slightly shorter main doesn't vent as fast!  That is, it doesn't heat as fast as the longer one with insulation. 


    I think the geography of the radiators plays a huge part in venting of radiators.  I ditched some of the brand new Heat Timer VariValves for Home Depot Maid O Mist #4 and #6.  In the room with the new Lux TX9000TS thermostat, I boiled an older Hoffman Adjustable now set to #6.  VariValves are too fast in some situations as stated in the vent chart. 

    All the radiators seem to heat at about the same rate regardless of size and location. 
  • Boiler Talk
    Boiler Talk Member Posts: 136
    edited March 2012
    Insulation for piping

    Reading further on this site if found a thread about a pipe insulation.  The dealer below was provided. 


    I'm not saying you should only look here, but I found 1" insulation for a price here far better than I could get at any big box or at the local plumbing stores.  I'm in Northern NJ and all I found in the stores was 1/2" thick insulation.  I'll have to say I found 1" insulation but only for 3" pipes.  If I'd only looked harder.  If you are going to reinsulate, don't hesitate, buy online!  You'll get a better price even with shipping and tax.  Do it! to borrow a slogan. 

    UPDATE: Since insulating the remaining 14' of dry return, steam fills the shorter main faster than the longer side.  Oh, I can go on and on in making adjustments. 
This discussion has been closed.