Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Improved Venting

Hi there,

I'm working on improving the venting on my one-pipe steam system. One radiator is very slow to heat and a couple others hiss loudly and splutter. I plan to replace all radiator vents with new Vent Rite #1's but need some advice on the main venting.

Please see the attached drawing of the system along with the following stats.

Circuit Main Vented by Vent Rite #31 at location "A"

31’ of 2” pipe = .713 Cubic Feet

8’ of 1 1/2 “ pipe = .112 Cubic Feet

Total = .825 Cubic Feet

Partial Counter Flow Main With Dripped Return Vented by Vent Rite #31 at location "B"

From Boiler to Drip Return and Drip Return Back to Boiler

12’ of 2” pipe = .276 Cubic Feet

9’ of 1 1/2” pipe = .126 Cubic Feet

Total CF/Ft. = .402 Cubic Feet

Counter Flow Branch

26’ of 2” pipe = .598 Cubic Feet

I believe that the Vent Rite 31's are too small and need to be replaced by something that can vent more air more quickly. I was thinking perhaps a Gorton #2 on an antler at location "A." The circuit loop is pretty straight forward. I'm a little more confused by the partial counter flow loop. It seems to me like the current vent at location "B" must only vent air from the 2" main running to the drip return and the drip return. I don't see how it can vent the counter flow part of the main. Would 1 Gorton #1 suffice there? There is no other main vent in the system and the radiator vents at the end of the counter flow main are responsible for venting all of the air from that long stretch, I think. Should I be installing another vent at location "C," perhaps 2 Gorton #'1s. Also, the counter flow pipe is very close to the ceiling and I'm not sure I can get a vent onto it properly at location "C". What about increasing venting on those two radiators instead?

Please advise. Your input will be greatly appreciated.


  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,395
    Vent-Rite #1

    The Vent-Rite #1 has a .09375" vent port. That's about the same as a #6, so your venting capacity is limited to about .24 cfm with the port opened up all the way. You might need more than that for the "very slow" radiator.

    You're right about the Vent-Rite #31s being too small. Normally you want to vent the mains very quickly so the steam starts to enter all the radiator takeoffs at the same time. Then the venting capacity needed for each radiator can be determined by adding the volume of the takeoff to that of the radiator itself.

    The standard main vent is the Gorton #1 or the Hoffman #4 or Dole #4, which vent .54 cfm. That's about six times the rate of your Vent-Rite #31s. Since you apparently have a 1/8" FIP tapping, you might want to try a Gorton #D, which has a .19" port and vents at .44 cfm. It's the same size as the other Gorton radiator vents, so it should fit without any modifications.

    The vent on your countercurrent main is in about the right place. It could be a little farther out, where the tee is, but it's working, so I wouldn't move it.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • counterflow venting

    don't make any changes yet to the radiator vents. put on enough main vents so that your back-pressure will drop to 1 ounce on your good low-pressure gauge [do you have one?]

    when you have arrived at that result, then put hoffman 40's on all the rads. if one or more have a tall long riser, there may be a need to put on one faster vent on that radiator.

    the desired result is that the steam will arrive at all radiators simultaneously.

    the undesired result is that the radiator vents will be doing all the venting, putting money in the pockets of the fuel company, and making a very uneven heat.--nbc
  • greengiant
    greengiant Member Posts: 19
    Vent CFM Specs and Venting Arrangement

    Thanks so much for responding. It's good to know of the choices for main vents (Gorton, Hoffman, Dole). I've been searching for info about cfm venting capacities for vents and really can't find the info anywhere. How did you know the cfm ratings for the various vents?

    Also, I just wanted to clarify. Currently there is NOT a vent at location "C". I'm thinking there should be. I'm thinking that it should be capable of venting the pipe starting at the point where the drip return starts back toward the boiler (yellow section on the diagram). Also I'm thinking that the vent at "B" only needs to be able to vent the section of pipe that runs from the boiler to the point where the drip return starts and including the drip return (blue section on the diagram). This arrangement would mean that the vent located at "C" would be larger than the vent at "D". Does that make sense?

    Again, thanks for responding. Your input is helping me to choose the vents to order for this project.
  • distorted text?

    i wonder why my text has lines through the last part--nbc
  • greengiant
    greengiant Member Posts: 19
    I have

    the standard pressuretrol that came with the boiler. Are you saying that I should add a vaporstat (I think that is what they're called)? They measure in ounces and can be adjusted for pressures between 0 and 1? My boiler is on the large size so I don't know if the pressure will be able to be much lower than it is without shortcycling. What do you think?

    Thanks for your input. I appreciate it.
  • Dave in QCA
    Dave in QCA Member Posts: 1,766
    Try the Edit feature

    NBC, not sure why the text put the strikethrough in it.  I can't find how to turn it on and off, but you might try using the edit feature and going back in and retyping that section, then deleting the strikethrough part.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • Steamhead
    Steamhead Member Posts: 14,840
    What I'd do

    is remove the vents from locations A and B. There is no need to fill those return lines with steam, since they do not supply any radiators.

    Get two Gorton #D vents. Drill and tap for one at location C, and the other at the very end of the 2" main where you have marked "very slow radiator". You want to drill and tap for 1/8" pipe thread on the side of the mains at these points.

    With this modification, the steam will go where you want it and not fill piping where it doesn't do any good. It will also let you fine-tune the radiators much better.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • greengiant
    greengiant Member Posts: 19

    for your input steamhead. I wondered why the mains at A and B were placed there. I thought maybe that venting there would somehow help condensate return but I don't really know much about it. It makes sense to put vents where you suggest. I'm just wondering, what will prevent those Gorton D's mounted on the sides from filling with water? Would the have to be placed on some sort of antler? Is one Gorton D enough venting or should I be using multiples?

    Sorry to ask so many questions but I just want to be sure of what I'm doing.

    Thanks so much.
  • Steamhead
    Steamhead Member Posts: 14,840
    edited December 2011
    The water in a steam main

    isn't much more than a trickle. So a standard angle-pattern type of vent that is screwed into the main on the side, where it is halfway between the top and bottom, won't see any water. It also gets around the height issue where a taller vent piped into the top of the main might not have enough space to fit.

    Based on the piping you have, one #D on each main should be enough. You can always add more if needed, but in my experience this will do.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,395
    Venting data

    I should have mentioned that my venting rates are at 1" wc of pressure, which is about .036 psi.

    I've basically been collecting data from all the manufacturers, some independent testing data and measurements I've made when I couldn't find it anywhere else. At some point I'll post all the data here and see if anybody has anything to add.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • crash2009
    crash2009 Member Posts: 1,484
    Venting data

    Gerry Gill and Steve Pajek tested a huge number of vents.  They posted the data here
  • greengiant
    greengiant Member Posts: 19
    I sort of did

    what you suggested with some modification. By my calculations I needed 4 Gorton D's. I put two at location C atop an 1/8" nipple. I put the other 2 on the riser just below the radiator, labeled slow on the drawing a few posts up, atop an 1/8" nipple.

    Is it OK to put a main line vent up on a rad riser instead of just after the last riser on the main? My thinking was that this would help to get the air out of the way quicker.

    Also, It is still taking 8 minutes, down from 12, for steam to hit the last radiator on this main. Any idea?.
This discussion has been closed.