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Looking for confirmation on main vent sizing (check my math)

So I have two mains, each with a Ventrite 35. My suspicions is that that are both undersized and due for replacement, based on comments in this forum and the fact that many of my radiator vents seem under strain, especially those served by the longer of the two mains. So I'm planning to replace them.

I've mapped out the mains my basement, meaning each main/return loop.

Main #1: 25 ft of NPS 2 pipe, with about 20 ft of NPS 1 1/4 return. I've calculated this to be about .775 cubic feet of air, based on the chart in Greening Steam.

Main #2: 15 ft of NPS 2 pipe, with about 15 ft of NPS 1 return. I've guesstimated this to be .43 cubic feet or less, as I'm not certain of the air volume inside NPS 1 pipe.

Since one main has substantially more volume than the other, it should have a larger vent. Looking at the Greening Steam / Gill chart on vents, it looks like the highest current-product main vents out there are:

Gorton 1: .33 cfm

Gorton 2: 1.1 cfm

Hoffman 75: .5 cfm

Maid-o-mist 1: .33 cfm

Since one of my mains is about 2/3 the volume of the other, I should have 2/3 the venting on it. Is the best course then two Gorton 1s on it, and one Gorton 2 on the other? I've also been warned that Gorton's have a max temperature threshold that I need to make sure my return doesn't rise above.

I'm doing this myself, so I'm trying to both not go overboard, and have a second set of eyes on this if at all possible!


  • BobCBobC Member Posts: 4,440
    Try this

    Use 2ea Gorton #1's on the long main (0.66cfm total) and one Gorton #1 and 1 Ventrite 35 (0.44CFM Total) on the shorter main.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • SteamheadSteamhead Member Posts: 11,375
    Bob's right

    that should work OK. As long as the steam reaches both vents within about 30 seconds of each other, and they don't take more than a couple minutes to fill with steam (measured from the time the boiler starts sending steam to the system) you should be fine. 
    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.
  • verbal329verbal329 Member Posts: 34
    Hmm....rad vents are still spitting and under pressure

    Yesterday I installed two beautiful new antler style main vent assemblies on each of my mains - dual Gorton 1's on the longer, and the hybrid Gorton/Ventrite on the other. 6" of clearance aboe the main below each.....ordered the materials from pexsupply.

    But I'm still getting a symphony of ugly sound in the morning - whistling from all of them, and spitting from a few vents upstairs. Plus the valves on two, and now possibly a third upstairs are starting to leak toward the end of the cycle. My intuitive sense is that the pressure 'seems' high, but the pressuretrol is set reasonably low, and my gauge seems to be both stuck at a reading of 6psi, and stuck fast in the boiler, so that I can't remove it to clean it. Sigh.
  • Main vent sizing

    Pexsupply doesn't sell the low pressure gauges so essential to diagnosing problems such as yours, but gauge (0-3 psi) does. Install it on the same pigtail as the pressuretrol, and then you can finish the main vent sizing. Add venting equally on both mains so that you can see the resistance to the air escaping in the back-pressure of venting. You want that back-pressure as low as possible, 2 ounces. In your situation I would have put Gorton 2's on each. Remember that doing the math gets you in the ball park, but observing the pressure gets you on the money!

    I would also put Hoffman 40's on your radiators

    Just leave the old gauge in place, as you do not want to break it it off in the tapping.--NBC
  • verbal329verbal329 Member Posts: 34
    Low pressure gauge

    Looks like is Valworx. Should I be ordering something like the following?

    I'll need to also figure out the right fittings and nipple configuration. Do I tee off above the pigtail, or below it? I suppose it shouldn't matter.
  • Mark NMark N Member Posts: 1,035

    You say it happens in the morning. Are you recovering from a set-back. if you are how much of a set-back are you using? Steam system work better without set-backs.
  • verbal329verbal329 Member Posts: 34
    Set back

    Yes, this happens only in the morning. We moved in to this house fairly recently (a month ago), and when we first moved in we got clanging in the radiators in the morning. I went through the house, shimming one end of the rads, and that helped. I then started insulating the header and mains, and that's when the real noise issues started. Assuming that the 'setback' refers to the differential between the night thermostat setting and the day setting, I do use one and it's about 7-8 degrees - the system setting is about 58 at night, and it comes up to 65 in the morning. If it's a weekday, then it is set back to 55 or so until just before we come home in the evening. This cacophony we notice only in the morning, when the system is ramping up from the setback, but I'm not home in the late afternoons, so I don't know if it's happening then too. During the 'temperature maintenance' firings over the course of the day the system seems to make all the right noises, that is very few.
  • Mark NMark N Member Posts: 1,035
    Recovery from set back

    That set back you are using is causing your problems. I've had steam heat for 25 years and I've learned it is best to leave it at one temp setting and leave it alone. I only set it back if we will be away for a few days and when I bring the house back up to temp I only raise the thermostat 2 degrees at a time. I would just leave it at 65 all the time.
  • verbal329verbal329 Member Posts: 34

    I'll believe anything at this point, but being the frugal sort I'm reluctant to leave it at such a high temp, even when we're sleeping or away from the house for several hours at a time.

    Separately, though, I still don't understand why what seems to be the act of making my system more efficient (insulating the header and mains) 'caused' such a strange response to the setback recovery. Maybe it is coincidence, and not causation, but peculiar nonetheless.
  • Mark NMark N Member Posts: 1,035
    Yea Really

    How long does the boiler run coming out of set back? Cold pipes make excessive condensate. Excessive condensate and steam cause water hammer. Excessive condensate from rads and steam cause spitting vents. Long run times recovering from set back can cause the pressure to rise as rad vents start to close. Long run time will cause over heating. How hot does the house actually get when the recovery is done?
  • verbal329verbal329 Member Posts: 34
    Recovery time

    Tricky question, for the morning - it seems like our thermostat is smarter than me, as if I tell it to bring the house to 65 in the morning, that's not when it kicks on - that's when it finishes. (actually, it finished early at around 6:20 this morning.) And yes, it has the correct date and time.

    I'm wondering if there is a local problem to two of my rads shared by the same runout, in terms of a slope pitch problem.

    Our bedroom (upstairs) is definitely cooler than the foyer (downstairs) at the end of the heating cycle, and that's where most of the sound is happening.
  • Mark NMark N Member Posts: 1,035

    Are you using a Honeywell thermostat with intelligent recovery? If it is a Honeywell is it set up properly for steam? it should be set to 1 CPH(cycle per hour). This morning might not have been the best to see how things work. It was very warm here in New Jersey. Was it cold where you're located? If it was warm the temp in your house might not have dropped much over night.
  • JHprovidenceJHprovidence Member Posts: 51

    I would love to see pics of what you have done. I am trying to get my landlord to add main vents on my system and it would be great to see how someone else added mains themselves.
  • verbal329verbal329 Member Posts: 34
    Mains vents pictures

    Below should be pictures of the mains vents I added. The antler with two Gorton 1's is on the longer main, and I re-used one of my old Ventrite 35's along with a new Gorton 1 on the other, shorter line.

    It is a Honeywell, but I'm not sure which model....we didn't install it, and it's a bear to get it open. No reference to cycles is available in the push-button menu, but maybe there's something behind the plastic cover? (Again, a huge pain to get it open.)
  • verbal329verbal329 Member Posts: 34
    ..antler for mains diagram

    Below is the sketch I stole from this site, and reproduced using 3/4" black pipe nipplesand fittings from Thanks to whoever originally submitted this....

    It was indeed warm last night and this morning, the system didn't come on at all. I re-shimmed the bedroom rad and the adjacent office rad, but haven't looked inside the built-in linen closet yet, which is where I think the runout times I feel like I've heard a lot of clanging and gurgling in there, which would imply (to me, maybe not others) bad pitch.
  • verbal329verbal329 Member Posts: 34
    installer setup for thermostat

    Sounds like you get to the 'installer setup' in a honeywell unit through a series of button pressed. My 3 year old is up now, so that will have to wait to tonight - but then I'll check for single cycle heating.
  • JHprovidenceJHprovidence Member Posts: 51
    nice job

    looks great. Thanks for putting it up.
  • Kev3bKev3b Member Posts: 18
    edited November 2013
    Honeywell pdfs

    It's a Honeywell RTH6350/RTH6450

    Below is the link to the installation guide.  The part you're going to be interested in is on page 17.

    Also, if you go to the Honeywell website, you can find the operating manual.  You have the ability to turn off the "System Recovery Function" if you don't like it.  With the function off, the system will turn on and off at the designated time.  With the function on, the system adjusts to have the thermostat satisfied by the designated time.  With the function off, it may be easier to time how long your system runs coming back from recovery. 

    In  regards to using a setback, if you look through "the wall", many people use little to no setback.  At most, I would use a 4 degree rollback at night.  Deep setbacks can be too much for the system to recover from, and can end up costing more than saving. 

    Full disclosure, I am not a professional, just a homeowner.  But, I do own the same setup.
  • verbal329verbal329 Member Posts: 34
    Steam recovery

    Thanks - I just went through the menu, and found the smart response portion. I won't be able to test that for a couple of days, but it will be interesting to see what the recovery time is.

    So it sounds like the conventional wisdom is to keep it to a 4-5 degree setback or less. I would think the amount of setback would matter less than the absolute temperature of the setback. If I keep the house at 85, with a 15 degree setback, I would think that kinder to the system than 65/55 or similar....because the ambient temperature of the 'setback' pipes would be higher in the first example.

    Right now, sitting here watching my son take a bath, I set the thermostat at 68, from the original 65. Several vents are whistling, and sounds like they're about to launch. The common element seems to be that they're on the longer run, that I just added two Gorton 1's to.
  • Mark NMark N Member Posts: 1,035
    Conventional wisdom

    The conventional wisdom with steam is to set the thermostat to 1 temp and leave it alone.

    Chose a temp that you find comfortable and let it be. An oversized boiler can cause whistling vents. What boiler do you have? How many radiators do you have and are you able to calculate how many square feet of EDR they have? Is the thermostat set to 1 cph?
  • Kev3bKev3b Member Posts: 18
    edited November 2013
    Agree With Mark

    Like Mark, I don't use a setback.

    I noticed in a previous post, you have Ventrite adjustable #1 and USAV radiator vents. Which are making noise. The USAV are cheapos that can be found at HD and are always going to make noise.

    Graphite packing on the valves will eliminate noise there. Undo the nut, wrap some of the packing around the stem and re-tighten the nut down. It'll act as a washer, as the old ones are most likely worn.
  • verbal329verbal329 Member Posts: 34

    It's a Burnham Indepedence PIN7SNI-ME2. I have 11 radiators that seem (to me) mostly medium to large in size. I haven't calculated the EDR for them all, as I wasn't sure (using the Greening Steam book) what class of rad they fell under (there were 4-5 types, if I remember right, and I didn't know if they were 'cast iron column' or a different type).

    Earlier in my steam experience I made a rookie mistake and started a different thread with a (barely) different that thread I uploaded pictures of all my rads. I'll do the same below.

    I don't know that my thermostat can be set to 1 cycle per hour, but it did give me the option of choosing 'steam' as my heating method.

    Foyer #1: waist high, 10 columns, Vent-Rite #1

    Foyer #2: waist high, 10 columns, USAV 880B

    Living Room #1: waist high, 11 columns, Columbia Metal Box Co enclosure, Dole "Syphon" vent (looks old)

    Living Room #2: knee high, double wide, 15 columns, Columbia Metal Box

    Co enclosure, Dole unmarked (no visible model number) with flat-head

    screwdriver turned control dial...looks old

    Dining Room: knee high, double wide, 13 columns, Columbia Metal Box Co enclosure, Dole #1933

    Kitchen: knee high, slim, modern, 22 columns, Vent-Rite #1 w/ dial

    Bedroom: waist high, 8 columns, USAV 880B

    Bedroom: waist high, 8 columns, Vent-Rite #1 w/ dial

    Bathroom: waist high, 5 columns, USAV 880B

    Master bedroom: waist high, 9 columns, USAV 880B

    Office: waist high, 6 columns, USAV 884
  • verbal329verbal329 Member Posts: 34
    pics of boiler and header

    Some more (duplicated) pictures of the boiler and header. I think I'm supposed to have another riser coming directly out of the boiler, but I have only one.My pressuretrol is set for just under 2psi, with a 2 psi differential, but the pressure gauge is stuck at 6 psi even when the system it's been suggested that it's clogged, and that I should add a 0-3 psi gauge to the pressuretrol pigtail.
  • verbal329verbal329 Member Posts: 34
    valve packing

    Does the fact that this leaking around multiple valves occurred simulatenously, and 'all at once', imply anything? We didn't experience the whistling, moaning, or leaking at all until I started adding insulation to the header and least in our brief experience in the house so far, anyway.
  • Mark NMark N Member Posts: 1,035
    Boiler and rads

    An IN 7 is rated for 542 sq ft of steam. As for your what you are calling columns are actually sections. Each section contains either columns(each section only connected at bottom) or tubes(each section connected at top and bottom). Count the number of tubes or columns in each section and the number of section and it's height. There is a PDF, I think it is on the Burnham site to help figure EDR for sizing a boiler. You seem to have a collection of different types of rads. Once you know the total EDR it will be easy to determine if the IN 7 is properly sized for you system.
  • Whistling vents

    When you finally get your pressure down, and your main venting made adequate, you will not be able to hear your radiator vents whistling. That whistling is music to the ears of your fuel company, as they supply extra fuel to push the air out!

    When you consult the radiator charts to find the EDR , you will need to use a tape measure, as it is so much more accurate than using body parts!--NBC
  • verbal329verbal329 Member Posts: 34
    Counting sections

    Thanks....I'll check that out. Suppose the boiler is oversized, is there anything to do about it?
  • verbal329verbal329 Member Posts: 34
    Lowering pressure

    So I've read all over the wall, and in Greening Steam, to turn down the pressure - and I know how to turn a screwdriver counterclockwise. But is there anything I need to consider before doing so? And how do I assess whether my main venting is now 'adequate' or not? Superficially, it should now be a lot better - 3x to 4x per main, depending on which one....but how do I assess whether that portion of the system no longer needs attention?
  • "No longer needing attention?"

    Another point to investigate is the diameter of the riser pipe coming up from the boiler-is it the specified size? Use a string to measure the circumference, and post that here. If it is too small,then the steam (with the lack of adequate main venting) will push excess water up into the radiators.

    Where does the smaller pipe teeing off the header above the boiler go?

    Even though you know how to use a screwdriver, you will not know how far to turn it, without a proper gauge, as those markings on the scale are notoriously inaccurate. The installation instructions suggest that the settings be verified using a gauge.

    You will know when you no longer need to pay attention to the venting, when the symptom (whistling) stops.--NBC
  • verbal329verbal329 Member Posts: 34
    edited November 2013
    Radiator EDR Calculation

    I calculated the total square foot EDR for all the radiators in the house, based on tables provided by Columbia Heating Products Company (I didn't find a Burnham reference). I tried putting in the whole table, but the formatting doesn't carry over in to the post properly. The summary:


    Total EDR sqft


    Foyer #1


    Vent-Rite #1

    Foyer #2


    USAV 880B

    Living Room #1


    Dole 'Syphon'

    Living Room #2


    Dole unmarked

    Dining Room


    Dole 1933



    Vent-Rite #1



    USAV 880B



    Vent-Rite #1



    USAV 880B

    Master bedroom


    USAV 880B



    USAV 884

    Total sqft EDR: 666

    This does not include the risers or mains, so it seems like the boiler is actually undersized, rather than oversized...but I had to do some interpolation in the table, so I could easily be off by the 20% mismatch between the two numbers.

    NBC asked about the size of the risers; they are NPS 1 1/4.
  • verbal329verbal329 Member Posts: 34
    edited November 2013

    Risers leading to the rads appear to be NPS 1 1/4. Risers coming directly out of the boiler, into the header, are NPS 2.

    ....I also calculated the total house rad EDR (excluding mains and risers) to be 666, which exceeds the boiler size by about 100 sqft.
  • Mark NMark N Member Posts: 1,035
    Rad Sizing

    It looks a if you may have used the wrong factor to determine the sq. ft. of EDR. The column rads you have I think should be 5sq.ft. per section not 7.5.
  • verbal329verbal329 Member Posts: 34
    Zounds! are exactly right, I was off by a row for the 3-column units that are ~36" tall. Having changed their EDRs to 5 per section, I now get about 510 EDR total.
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