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Inadequate Main Vents

Samitch Member Posts: 1
Hi All! Thanks for all your contributions, as a new homeowner, I’ve learned a lot and was able to make huge improvements. However, I think I’ve hit the limit on the “easy items” (proper pitching and radiator vents) and need to move into bigger items.

My problem is long hissing vents and it forcing a long cycle because it’s not heating up the pipes quickly. No water is coming out of the vents, the worse offender can hiss for 20+ mins and not even be warm while the rest of the radiators get hot. It’s set to the largest vent opening, air vent was replaced, and all other air vents reduced to try to encourage steam to go there first. It’s loud enough to wake me up 3-4 times a night. 

My one pipe system has only 2 Main vents that are located to directly next to the boiler on 2 out of the 3 pipes going out. The pipe without a vent is very short and goes to the kitchen then the faulty radiator up top. Am I right in assuming that if I add a main vent to this pipe, this should help it vent faster? 

The challenge also becomes that I am assuming that kitchen one goes up to the bedroom because that is how our other 1st and 2nd floor radiators work. Some time in the 90s they reno’d the kitchen and most likely moved that pipe behind a wall. They made… a lot of not great choices during this reno.

While the rest of the piping has vents, it seems inadequate. They run 40 ft to the next room and 80 ft to the further corner with 2” pipe. 

Would this help the system heat up faster, quieter, and more efficiently? (Natural Gas bill was almost $300 last month)

From what I’ve seen, I would need Gordon main vents, not Ds but the size down? And a drill and tap. Is there anything I’m missing? Is this really better handled by a pro? 

Pictures attached, unfortunately a different bad reno hid a lot of the further piping under a drop ceiling and asbestos. 


  • Jamie Hall
    Jamie Hall Member Posts: 22,881
    Main vents would help -- and there is no point to going small, unless budget constraints force you to. The bigger the better, in general. That total 120 foot should probably have a #2. The vents next to the boiler are probably not doing anything useful. Probably not hurting anything, but... no doing anything.

    On the line that goes upstairs, it may be easier to put a main vent near the top of that riser upstairs, rather than in the basement -- but before the radiator takeoff.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England