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air vents

I recently repaired a leak on a cast iron radiator. It was venting through the leak and was always the hottest one in the house. I have since replaced the air vent with a danfoss type air valve with an upright vent. I did the same thing in another room in which the radiator was also cranking heat, unregulated, and now both radiators are barely heating up. Air vents out (valves open) but then close while only heating maybe 1/4 of the radiators which then cool off quickly. So now the solution to my overheated rooms is working to the opposite extreme. Not enough air vents out to allow a middle ground of heating each room. both are on the second floor and are fed from the middle of the main from the basement. Also, one of these radiators vents very wet ( the only one in the house) with a very slight hammer and sounds as though there is water in it. Do I just replace the air valves with vents only? that seems the obvious choice but I was hoping to regulate the heat?


  • neilc
    neilc Member Posts: 2,667
    pictures, of both rads, from both ends,

    Are the rads pitched back to the supply valves?
    Are the supply valves fully open? they should be.

    Are the vents closing, steam hot, or are the TRVs closing down?
    you may be venting too fast, and the steam shooting across to the vent, before heating the rad,
    What type vents?
    maybe try without the TRVs.
    known to beat dead horses
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,849
    I recall a couple of instances where radiators shut down prematurely because the vents were too fast, allowing steam to hit the vent without completely filling the radiators. Could this be happening here as well?
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • 638agent
    638agent Member Posts: 3
    valves and pitch are good.

  • acwagner
    acwagner Member Posts: 505
    Silly question--are the rooms comfortable?

    Basically is the room warm enough at the start of the heating cycle and the TRV are working?
    Burnham IN5PVNI Boiler, Single Pipe with 290 EDR
    18 Ounce per Square Inch Gauge
    Time Delay Relay in Series with Thermostat
    Operating Pressure 0.3-0.5 Ounce per Square Inch

  • 638agent
    638agent Member Posts: 3
    no the bedroom is cold, the larger room/rad. and the heating cycle shuts down before the room rad gets any substantial steam to it. the rest of the house is comfortable with the thermostat.
  • KC_Jones
    KC_Jones Member Posts: 5,705
    First, if those are Danfoss, as near as I can tell you bought the wrong product. There are Thermostatic valves for water (goes on inlet to radiator) and there are Thermostatic valve for steam that goes on the vent. Here is a link to the steam version.


    Second in order to get them to work properly you need the correct size vent. If the room isn't reaching temperature due to the cycle ending you need a faster vent on that radiator. I and others on here advocate for getting as good a balance with venting first, then if you can't get the control you want go to the Thermostatic vent valve.

    Food for thought, with the "too small" vent you currently have you are showing how much control you can have without the Thermostatic valve since it isn't actually doing anything right now. You might have been able to fix this without spending the money on it.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • neilc
    neilc Member Posts: 2,667
    or is the steam vent getting steam hot and closing, before the radiator warms up ?
    known to beat dead horses