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Radiator vents

ChrisJ Member Posts: 14,948
If radiators are properly sized for the rooms and mains are properly vented is there any need for adjustable radiator vents?

And even if adjustable vents are required wouldn't this mean on very cold days when the system is going near full swing those rooms would still end up over heated because all rads would end up totally filled with steam anyway?

I was thinking of buying a bunch Hoffman 40's or Gorton 5s or 6s but wanted other opinions first.  I have seen threads about the Hoffman 1A's being questionable but none on the quality of the 40's.


Chris J.
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment


  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    Radiator Vents

    I am assuming by your question, that you are talking about 1 pipe steam. Yes, it is important to vent the rads as well as the mains. And, hopefully, the rads were sized properly for the rooms, and probably were, because the dead men often would build their own rads 1 section at a time, correctly sized for each room. Think of it as 2 seperate parts of the same system. You have the steam going thorugh the mains, and air is being squeezed out through the main vents, and hopefully, its vent is sized properly for the main. Double check this. Steam hits the main vent, then shuts, allowing the main to pressurize, hopefully only to ounces. Then comes the job of the radiator vents. They HAVE to vent the air out before the steam can get in. Remember, no two things can occupy the same space at the same time. Now, you have to remember, the rooms may have changed some since the system was installed, however long ago. They may have been insulated, so now you may have too much radiator for the room. The vents, by way of their adjustment, allow only the proper amount of steam to enter the radiator for the comfort of the room they occupy. As far as the type of radiator vent, you wont find a better brand than Hoffman.
  • ChrisJ
    ChrisJ Member Posts: 14,948
    edited June 2011
    But how useful are variable vents

    Hi Greg,

    Yes it is a 1 pipe system.  I still have my doubts as to how useful adjustable vents can be.   Say I set up four radiators in four rooms all to vent at different speeds.  If the system runs for a short amount of time occasionally the rooms with slower vented rads will stay cooler.  But the longer the system runs the more time those slower rads have to fill up.

    To me this means the colder the days the closer the slower vented radiators come to the normally vented ones making the adjustable vents kind of pointless.

    The reason I brought this up is I was considering buying a 12 pack of Hoffman 40's and replacing all of my vents with them.  Currently the system has a mix of LDR and heat-timer valves.  Some are adjustable and some are not.  I just bought the house and was able to run the heat a few times before it got warm out. Neither main vent worked and of course the system as a whole works like garbage. 

    I am replacing the main vents with Gorton #1's as per steamhead's recommendation though I realized one of my mains was longer than I originally thought so I will be using three Gorton 1's on that one (2.5" pipe @ 29 feet) and 1 on the other (2.5" @ 11 feet). 
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    Vent Questions

    I understand your dilema. But, you have to take into consideration that the venting rate is everything in steam. The faster the air can get out, the faster the steam can get in. Then, the the entire system will heat more quickly. If the current vent rate does not meet your needs, crank them up a notch or 2. The tstat location is also a factor in this. Has it been changed? Is it in an area that was once an open area, but now may be divided off? This is all stuff that has to be taken into consideration. Varivents are a great vent also, and standard non-adjustable vents would be fine, but only if you were sure that that fixed rate is what you need. Generally, it is not. Replace your main vents first. Make sure you have the proper vent for the main(s). Make sure also, that it is installed properly. A correctly sized vent installed improperly can be as bad as no vent at all.

    If you still are having problems, I would recomend that you find yourself a good steam guy, to come evaluate your system for you. His maintainence, and corrections, can save you a lot of money, and give you a lot of comfort.
  • crash2009
    crash2009 Member Posts: 1,484
    You need to get yourself a copy

     of "balancing steam systems using a vent capacity chart"  written by Gerry Gill and Steve Pajek.  The hand book is available here on the website for 10 bucks.

    The hand book explains in detail better than any 10 of us could explain here in a post.  Venting, basicly, should be approached as two different problems. 

    Problem one is the main vents.  Get the steam to fill the main line as quickly as possible. 

    Problem two is the radiators.  Slowly let the cold air escape through the rad vent. 

    At 2 oz CFM, the Hoffman 40 vents at .067 period, there is no adjustment.  Maybe you will get lucky and find out that's what you need.  But if not, you are married to it, until you replace it.

    The Ventrite #1, has 8 individual settings, ranging from off to 0.020 and all the way up to 0.125 The Ventrite can be 7 different vents in 1, and is my favorite. 

    A lot of people, new to steam, including myself, thought that the radiator needs to be hot all the way across, all the time, to be working correctly, but this is not true.  Most of the winter mine and others only heat the first 3 sections.  Mine don't heat all the way across until it gets very cold 0 F to -10 F.  This is the only time my radiator vents get to feel the steam.  The rest of the time all they do is let out the cold air and let the cold air back in.

    If you get the hand book, and calculate how many EDR you have on each rad, the book will recomend the size you need.  Until you measure and calculate the size of vent needed, anything is a guess at best.
  • Dave in QCA
    Dave in QCA Member Posts: 1,777
    edited July 2011
    Vent selection and Adjustable Vents

    Chris, you are correct on your point that regardless of the venting rate, on a very long steaming cycle, all of the radiators, even the ones with the slowest vents will, or likely will, fill with steam.  There are two big points to consider though; 1.  That the vent selection will affect the comparative speed with which the various radiators in your system will fill with steam, and 2.  You will find that your system will probably rarely run long cycles where all radiators will completely fill with steam, especially a radiator with a very very slow vent.

    Boiler Pro, aka Dave Bunnell's mantra is " vent your mains fast and your radiators slow, but completely."   The whole point is to get even steam distribution and even heating of your radiators.  In a properly vented one pipe system, the steam should begin to travel down the mains toward the main vents.  As the main vents close, steam should begin to enter each radiator at about the same time.  You will not get this to be perfect, but that is the goal.  The next thing is that you want the radiators to fill with steam at the same approximate rate.  This is not to say that you want all the radiators to fill 5 sections at the same time, because you probably have a variety of sizes of rads in your system.  So, what you want, is for all the radiators to reach 25% filled with steam, 50%, 75%, etc at the same time.    So for 50%, a 4 section radiator would be have only 2 sections heated while a 20 section radiator would have 10 sections heated.  If you use all of the same vents, i.e. Hoffman 40, you might get good distribution, but it will be dependent on your system piping and the fact that different radiators will have different sized feed lines.  Often what you will find is that the rooms with the big radiators will be cooler that the others because that big radiator is vented at the same as the little rads, and is not heating at the same proportional rate. 

    Here comes the application of an adjustable vent, you could get a good reliable adjustable and fine tune it so that the big radiator is heating at the same spead as the smaller ones.  Once you get it set right, you leave it alone.  

    Crash recommends Ventrite brand, they are a good reliable vent and the adjustments are accurate. 

    Another approach, you could use the Gill & Pajek balancing information, and it should help you get your system finely tuned with fixed rate vents based on the relative sizes of your rads.

    In answer to your question regarding Hoffman #40 vents, you might find that your system works very well with them.  They are a reliable good quality, very quiet, slow vent that tends to bring a system into balance.  I have seen systems with all Hoffman 40 vents, and the often worked very well. 

    The vents that will cause problems are those that are too fast.  Those tend to be the Heat Timer Varivalves, Hoffman 1A (on all but the slowest settings), etc.

    If you can get a good deal on a 12-pack of Hoffman 40s, it might not be a bad choice.  Recently, I rebalanced a system that was totally messed up.  It originally was totally vented by Hoffman #40 vents.  Someone who installed a new boiler threw in a bunch of Hoffman 1A vents on the first floor.  It totally messed up the balance, with some radiators fully heating very quickly and others on the first flloor, even with a fast vent, not getting any steam at all.  A bunch of vents that are too fast will to that to a system.   The Alpha Male Radiators will take all the steam for themselves, and nothing gets to the runt at the back of the pack.  Slow vents will prevent that from happening.

    When I reset the 1A vents so that they were venting the same as the #40s that they replaced, everything came into balance.
    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.
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