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Steam radiator venting

Vent sizing

I have an academic question to check if I am understanding one pipe steam venting correctly (because I am about to reinstall my new radiators and need to order vents, and I want to land in the right ballpark).
Please excuse my nomenclature, I am not sure what all the proper industry terms are.

Let’s say you have existing steam system in the basement that feeds a three story house. The big pipe (main?) that supplies everything before it turns up is optimally vented and insulated. If I wanted to get steam to every radiator at the exact same time, in the theoretical world (and I am not suggesting a person do this), would this work?
1. station an elf with a stopwatch at every single radiator connection, have the valve wide open
2. Once the steam reaches the main, have every elf time how long it takes the steam to get to their location.
3. Install a vent Before the radiator according to the charts in Dan’s book to vent all those fast.
4. Calculate the volume of air in the largest radiator and pick 2 radiator vents that will allow that radiator to fill slowly but sufficiently.
5. Extrapolate what rate you would need to fill the other radiators so that they also fill in the same time the big radiator fills.
If all that was done precisely, would you have a perfectly balanced steam system?

Then as a follow up to that, I have a third floor sunrad that lives in the wall. The supply to that is buried in the wall. Is there a way to vent the supply pipe separately from the radiator?

In the absence of my steam elves scheme, if I want to vent the vertical pipes (are those still called steam mains?) separately from the radiators, does that mean replacing the shutoff valves? Right now I have the kind that the pipe goes up into it, and the turney-wheel thing sits on top, and the connection to the radiator is on the side.

And practically speaking will I see any appreciable performance increase in venting the first and second floor vertical pipes separately from the radiators if they are only supplying one radiator each?

Thanks in advance, you guys are a such a great resource.



  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,838
    So, where are you going to get enough elves to spend the time to do this controlled experiment, this time of year? Please consider that all the elves are out working on shelves now.

    Theoretically, if you wait until after December 25, there will be a large number of elves starting on holiday. There may be better chance of having a successful outcome when your staff is not under the stress of deadlines for providing information for a much more important list. The Naughty and Nice list!

    I hope you find this information helpful
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • gfrbrookline
    gfrbrookline Member Posts: 753
    I wouldn't worry about venting the verticle pipes, called runouts or risers depending on the application. I would start with Ventrite # 1 adjustable radiator vents set to 4 on all the radiators and see where you are. They can be purchased at https://www.patriot-supply.com/products/showitem.cfm/VENT_RITE_1. If your mains are vented properly in the basement you should not need additional venting.

    Rooms that overheat turn them down, under heating turn them up. If your third floor radiator is not heating enough slow the venting down on the radiators below it, that will entice more steam up to it.

    You will likely have to do this yourself as elves are very hard to come by in this economy. I tried to hire 35 at work and only 10 passed the drug test, 4 quit within a week when they figured out we actually wanted them to work and not stand around looking at their phones.
  • nicholas bonham-carter
    Make sure your main vents are adequate enough, because they do most of the air removal work. If you have a low pressure gauge, the venting should take place at less than 2 ounces.—NBC
  • ethicalpaul
    ethicalpaul Member Posts: 5,702

    Make sure your main vents are adequate enough, because they do most of the air removal work. If you have a low pressure gauge, the venting should take place at less than 2 ounces.—NBC

    I love this advice. If it were me with what I know today I would put #4s (gorton or maid o' mist) on every radiator, see how it goes for a week and then put a number 5 on any cold rooms. Then run another week and put a 6 on any that are still cold.

    But first by a mile is to get the main venting working completely and watch it work during several calls for heat to understand how the steam moves.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el