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How much water loss through single vent?

gibson Member Posts: 15
About how much boiler water could be lost (per day) if a main air vent is stuck open? I am losing a quart a day and am wondering if this could be caused by steam escaping a single faulty vent. Or do I have to look for another cause? Thanks.


  • conversiontime
    conversiontime Member Posts: 87
    edited January 2014
    possibly but seems high

    If the boiler is large and runs many hours a day then possible. If you observe the main vent spitting actual water vs some spittle then very possible but I would check elsewhere for leaks, are the returns accessible or under concrete/floor? If no visible leak at boiler then returns are often suspect.
  • gibson
    gibson Member Posts: 15
    Returns are above ground

    All the returns are above ground. The boiler doesn't lose water unless it's working hard, so that means that the loss is in the form of steam (above the water line). I overfilled the boiler to see if it had any leaks that allowed steam up the chimney, but found nothing. Either the steam loss is from the open vent, or hidden somewhere in a wall.
  • conversiontime
    conversiontime Member Posts: 87
    assume you checked all rads

    They can leak from vents, valves, risers and in some cases the radiator sections themselves. Look for black staining on the floor under and around the rads. Even so you would probably know if a quart of water was dumping on your floors every day. If vent is losing that much water you should see it condensing nearby, either on wood, ceiling, etc. You could even try to trap how much the vent loses by placing a suspended metal pan or something over the top that then condesates/drips into a collector set underneath.

    I say it seems high b/c I spent one whole season running my system on too high of pressure before reading Dans books. Every rad vent and many valves hissed like crazy regularly one in particular that never close gushed steam non stop. And even then I was adding 1qt maybe once 10  days.
  • gibson
    gibson Member Posts: 15
    That's a lot of water

    If I put a mirror on the vent, it steams up pretty good. It's a straight vent on a vertical pipe, so it's a little hard to collect the water from it. I'm sure its causing some loss, but not a whole quart per day. I know that the radiator vents are good because they are quite new and I tested them, but I'll inspect radiator joints etc and see what I can find. Thanks.
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,849
    Could be the return.

    Water backs up farther in the return during heating, and even dry returns can develop leaks. It's not the typical pattern, but if yours was the typical case you'd have found the leak by now.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24