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How Many Vents for Main ?

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CommAve
CommAve Member Posts: 6
Hi,
I'm trying to balance out a single zone, steam heat, 5 story (plus full basement) apartment building and I'm replacing many of the radiator valves in order to do so. The front of the building is about 100 feet from the boiler and always under heated.

The distance from the boiler to the two furtherest risers is about 100 feet and the main is 6 inches.

Is a single Gorton #2 or Hoffman 75 on each main sufficient ? If not, how many vents should I have at the end of the two mains, before the risers ?

Thank you.

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  • JUGHNE
    JUGHNE Member Posts: 11,075
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    Rule of thumb is one G2 for each 20' of 2" pipe.
    Barnes & Jones Big Mouth does twice that.
    That is for 2". If all of yours is 6" then you need a lot if there is none.

    I would not spend the money on the Hoffman 75, only about 1/2 venting of a G2.
  • CommAve
    CommAve Member Posts: 6
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    Thank you for your reply. Right now I have one 3/4" Hoffman 75 on each.

    So you're saying 5 G2s or 3 Big Mouth's ?
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    A 3/4" pipe opening can only pass about 4.3 G2's worth of air, you could add the existing 75 to 4 G2's on an antler arrangement.

    G2's and BJ Big Mouth's are about the same price...…
    But the BM does not have a float to keep any water inside if you get some flooding situation. G2 & 75 does.

    Again that rule of thumb was for 2" pipe, any increase in venting will surly help your situation though. IMO
  • ChrisJ
    ChrisJ Member Posts: 15,774
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    A 6" pipe has 9 times the volume of a 2" pipe.

    My guess would be you need 9 times the venting that a 2" pipe requires.

    @gerry gill What are your thoughts?
    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
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    You might have vents or plugs at the top of the risers on the 5th floor. That would help things a lot.

    Page 133 of Greening Steam shows some other options, being how you are changing some rad valves.

    BTW, is this a one or two pipe system.?
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    edited October 2018
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    I have a somewhat similar system, with 6 dry returns coming back to the boiler room. Each one has 4 Gorton #2 on it, (big mouthe we’re not available then).
    Don’t spend your money on new radiator vents, unless they are non functional. The main vents do all the work of letting the air escape with low resistance, instead of having to be squeezed out through a constipated undersized main vent. Don’t pay extra for the fuel company to force your air out each heating cycle.—NBC
  • CommAve
    CommAve Member Posts: 6
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    Thank you all very much for your responses.

    No expert (but learning fast) but I think it is a one pipe system when suppling the radiators, but there seems to be a 2 pipe loop (supply and return I guess) in the bathrooms. There is a return back to the boiler for what I guess is water / condensation.

    The reason I'm replacing vents is because most of the heat is on lower floors and in the back of the building where the boiler is. Plus the handyman has been installing adjustable vents and Gorton D vent in any unit that didn't like just 70-75ish degrees heat. So I think that is out of balance.

    Good point about my heating contractor. I asked them to add more vents and they basically said "if you hear any air coming out of the vent then it's working" and said that's good enough. But the problem of all the heat in the back of the building still persists.

    I think I'll try adding vents in the antler configuration as suggested, see how that works and take it from there.

    Any other advice is appreciated.

    Thank you.
  • CommAve
    CommAve Member Posts: 6
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    Meant to say:

    There is ALSO a return back to the boiler for what I guess is water / condensation.

    The reason I'm replacing VALVES is because most of the heat is on lower floors and in the back of the building where the boiler is.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    If the thermostat is in the lower floor, then it is generally satisfied before the upper floors get adequate steam, due to the lack of main venting slowing things down further away from the boiler.
    With proper venting, the steam will fill the mains, and dry returns first, and then rise up towards the top floor, and into the radiators on each riser.
    Some tall buildings will have “downfeed risers”, which deliver steam to the top first, and then moving downward to the takeoffs for each radiator, evening out the natural tendency of the upper floors to be colder.
    If you have a Honeywell VisionPro with remote sensor mounted in the colder part of the upper floor, it can sense when the temperature falls in that more exposed area, while you have the control under lock and key. You still need to balance out the venting to avoid overheating the warmer areas.—NBC
  • CommAve
    CommAve Member Posts: 6
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    There is no thermostat in the building. Heat is controlled by a HeatTimer and there is sensor on the furthest riser as well as an outside sensor.
  • DropTheHeader212
    DropTheHeader212 Member Posts: 3
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    New here as well..I have lots of asbestos on my steam piping main. I need to add main vents because there is none. Instead of putting these at the end of the mains. Could I put them on the (2) returns right before they drop to the boiler? Less asbestos on the returns near the boiler.

    Also- one main is 36’ and one is 18’. Will a big mouth vent on each main be sufficient?
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    Yes, that is the best location: at the end of the dry return, just before it drops down to become the wet return.
    Put some elbows in the risers for each vent, to absorb the shock of any water hammer there.
    A Big Mouth on each is a good start, but you may need 2 on the longer main.—NBC
    DropTheHeader212