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more venting, another rad, and / or bigger pipe?

4Barrel Member Posts: 125
after a couple of seasons of fiddling, i've got three of the four apartments in my building heating pretty much in unison; the last apartment (ground floor w/ more heat loss) is proving to be quite stubborn. my EDR calcs show i;ve got more potential heat in that apartment than any other, yet it is still the coldest, and is slow to heat (the config of the apartment is a major impediment, but i can't do anything about that). the largest rad in the apartment serves the main room, which is also the coldest room. the rad is a total of 28' of pipe away from the 2" main (5' of 1.5' stepped down to 1.25' the rest of the way). there's a gorton #1 about 16' down along the 1.25" line, just after the final run towards the radiator in question. the 1.25 line continues to serve one more rad on an upper floor... the vent is not at the very end of the 1.25 run, but close.

i've boiled (pun intended) the fix down to three scenarios:

1) easy: add another #1 vent.

question: for a 1.25" pipe of the length discussed, is the gorton in place already venting that pipe to its maximum? is adding another going to have any impact?

2) sorta hard: add another rad to the main room. there is a place this can be done where the line steps down from 1.5" to 1.25" it gets a little messy tying in the dry return, but doable.

3) really hard: replace the 1.25" pipe with 1.5" - at least for the greatest length of the run before the branches to the rads. of course, i'd add more venting as well, prob a #2. but does bigger pipe mean faster steam, or just more air to vent? hate to do all this to find i'm in the same boat i'm in now.

obviously, it's easy to test #1, and i'm doing that. just interested in input on the bigger picture questions.

as always, thanks for reading and any responses.

PS - All pipes have 1" insulation.


  • cold apt.

    are all the rads getting steam at the same time , comparing the cold rads to other warmer ones on the same floor? will plates of butter all melt at the same time on all rads? this test also has the advantage of having some nice buttered toast at the end!

    if you have a good low-pressure gauge, then you can see the back-pressure of venting, which in my case is 2 ounces. this shows the resistance to the air escaping from the mains. as you can never have too much venting, i would put on the biggest one you can buy as the 2nd main vent on that run.

    if you have a big radiator vent in the vicicnity of the thermostat, then replace it with a slower one like a hoffman 40. in fact they are best for all the rads, except on a top floor problem area.

    an alternative, if you have a honeywell visionpro would be to mount its remote sensor in the cold area, and that cooler ares will trigger the system. you can set the temperature down, if the rest of the building seems to overheat. --nbc
  • icesailor
    icesailor Member Posts: 7,265
    Venting Rad:

    I'm not really qualified to answer this question. But I have a question. Do I understand that there is another radiator on this 1 1/2" line that changes to 1 1/4" and feeds the radiator in question? And continues to the second radiator? If so, does the second radiator get hot? If no second radiator, and the only radiator on the circuit/branch doesn't get hot, I'm waiting for an experienced thought.

    From what I have learned here, it seems that the ideal venting part of a steam system is one that has vents installed that will vent all mains and radiators at a rate where all air is vented at the same time. That some vents may need more venting resistance than others.

    What happens if you close off a few radiators, which cut down on the system load on the boiler? Will the radiator get hot?

    I'm interested.
  • BobC
    BobC Member Posts: 5,471
    What size radiator air vents

    Assuming the slope of the pipe and especially the feed to that first floor radiator are good, is the upper floor air vent larger than the one on the first floor? If the upper floor vent is larger it might be hogging the steam and depending on where the thermostat is it might be enough to give you a problem.

    A 1.25" pipe could support at 10-15 Gorton #1's for venting  but that pipe run only has about 140 cubic inches of volume (0.08cf) so that single #1 should be ok if it's working correctly. Have you timed the steams arrival at the vent to it's arrival at each radiators input pipe?

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Long Beach Ed
    Long Beach Ed Member Posts: 1,187
    Heat Loss

    You must conduct a heat loss calculation for each room and see if the radiators are properly sized to the heat loss. 

    That's always the first step. 

    Proper, uniform operation of a heating system is counterproductive if three apartments are over-radiated and one is under-radiated. 

    Often a system is purposely out of balance to favor a room or unit that has too little radiation or to slow steam to a unit with too much radiation. 

    This is especially common in multi family conversions were walls were moved and room configurations altered without a corresponding revision to the radiators. 
  • 4Barrel
    4Barrel Member Posts: 125

    great input - thanks.

    answers to all questions, hopefully:

    nbc -

    - no, not all rads in the same apt are getting heat at same time, although, i may do your butter test anyway ;-) the other ones have end runs branched closer to the 2" main (which has a #2 vent), so they heat a little faster. i've compensated for this at the rads (all have new 1A vents), slowing down the one closer to the 2" main, and speeding up the one in the bigger "cold" room. to compound the issue, the config of the apt has the warmer rads located in tighter spaces.

    - not sure exactly how to test the back pressure (where do i mount the gauge? in place of the vent?)... but i get the idea.

    - w/r/t t-stat, out of necessity, i've placed the sensor in the cold room of the cold apartment. i use a white rodgers t-stat with remote sensing, which has been very helpful is isolating the issue. if i place it in the warmer part of the the cold apartment, then the system cycles too quickly to heat the other apartments. if i place it in the cold room, it cycles longer than necessary, creating a rather larger temp differential from coldest to warmest apartment (as much as 5 degrees over set point). this has been the best compromise though, because I don't want the cold apartment too cold to be uncomfortable for that tenant. and, of course, no one else is complaining about being too warm. but, i know i'm wasting energy.


    yes, the 1.25 does continue and feeds another rad located on an upper floor, another apt. the #1 vent is located on the 1.25 run between it and the slow rad i've been discussing. yes, it also heats slowly, but due to a number of factors that go to heat loss, that apartment overall stays nice and warm.

    the rad in question does get hot, just more slowly than I want it to. closing off other rads really doesn't impact it.


    the feed to the first floor rad comes off the 1.25 run at 45 degrees up and then runs angled down so any condensate will run with steam flow to the riser, which has a dry return. I re-piped it this way last year, and it helped (before the feed line ran counterflow).

    the upper floor rad vent is also a 1A, and is set to 2. the lower floor 1A is set to 6.

    i have, in the past timed the arrival of steam, and the 1.25 run has always lagged behind. less so once the system is steaming more continuously. i expect the disparity to lessen once it gets colder out, but it will still be there.

    Long Beach Ed:

    I think you are absolutely on to the ultimate factor here. when i reworked the system two seasons ago, i juggled he rads, sizing up the "cold" room in the "cold" apt, and making many other changes. this resulted in more even heating in the building with the one exception. but you are right in that heat loss, versus just straight sizing per square footage, is what is driving the problem. i think, eventually, i will be adding a rad to this room.

    BUT, in the meantime, the fact that the 1.25 run heats more slowly is making matters worse. i am going to add another #1 and see what happens.

    thanks for all the input!
  • Jamie Hall
    Jamie Hall Member Posts: 22,897
    If it cheers you up any...

    I doubt that changing the pipe size -- the hardest option -- will help at all!  But I imagine that adding a new vent on the runout/riser will help.  Good luck.  I hope that that tenant is civilised?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 4Barrel
    4Barrel Member Posts: 125
    thanks jamie

    i'm pleased to put the third option out of my head!

    but you've given me another idea - instead of adding a vent to the location of the current, i may add it at the end of the runout for the slow/cold rad. thanks! will report back once completed.

    Happy Thanksgiving!
  • BobC
    BobC Member Posts: 5,471
    Error . . Error . . Error

    I stated your problematic pipe run only had about 0.08 cubic ft of air but it actually has more like 0.26 Cf so I have to agree with Jamie about the addition of more venting.

    Sorry for the screw up.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • 4Barrel
    4Barrel Member Posts: 125

    i didn't have another #1 handy, so that gave me another idea. i pulled a #1 from the main serving rads in two the warmer apartments (i had 2 on that main) and added it to the single #1 that served the 1.25 run out... pic of my new vent "antenna" attached... so simply put, i'm trying to slow down the warm main, and speed up the cold one.

    so far so good... the temp differential from warmest apartment to coldest is now about 2-3 degrees versus 5 before. however, it's been warm, so we'll see what happens when it gets cold and the cold room heat loss tics up...
  • 4Barrel
    4Barrel Member Posts: 125
    a footnote

    so this story wraps up this way: after a the change i described and some slight fiddling with rad vents, the so-called "cold" apt and "hot" apt are heating in unison, i mean right on the money. NICE, right?? well, now the tenant in the former "hot" apt is complaining that she  "feels" cold!   &^%##%^&**!!

    this would be an example of when a balanced system, even when accomplished, is not appreciated. oh well.
  • Abracadabra
    Abracadabra Member Posts: 1,948
    tenant is now cold?

    she probably "feels" cold because it was so hot before ;-)
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