Air in system

Discussion in 'HVAC Heating & Cooling' started by Barry J, Apr 6, 2008.

  1. Barry J

    Barry J New Member

    Messages:
    99
    Location:
    Mass
    I have oil heat with forced hot water. In January the oil co. came in and cleaned my furnance and purged the air out of my system..there was quite a bit. He siad it was either my air valve was bad or i was running my furnance too hot. The air valve looks new so, he figured it was my hot furnance, boiling the water. We put down the settings, which worked good, no big problems with heat or hot water.
    But, now I'm starting to get alot of air in my system again, especially my bedroom zone, sometimes wakes me up with the gurgling.
    My question is, ..with spring coming and me probably not using the heat, should i call the company to come out to purge the system or should I just wait until the fall heating season????
    And does that air in the system effect the hot water for showers at all?? That must be separate right???
    Thanks
    Barry
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
    The boiler water system should be essentially air free. The reason for this is to keep corrosion down and allow proper flow to go where it needs to. The circulator pumps often can't push water through the upper radiators if there's too much air in the system.
  3. Barry J

    Barry J New Member

    Messages:
    99
    Location:
    Mass
    I can't figure out if that answered my original question, all I want to know is ....with spring coming and me probably not using the heat, should i call the company to come out to purge the system or should I just wait until the fall heating season????
    And does that air in the system effect the hot water for showers at all?? That must be separate right???
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
    Shutting off the system allows the water to cool. Colder water is more dense. If there is a leak, the resulting vacuum might pull in more air. But, without circulation, some of the seals might also dry out, and if you fixed it now, you might have new leaks in the fall when you turn it back on.

    Assuming you have an indirect WH, the boiler itself will remain on during the summer. If the lower loops also contain air, then yes, the heat transfer will be less efficient, causing the boiler to run longer than needed to keep the water hot for showers, etc. But, will it fail to keep it hot - probably not - it will be able to keep the water hot.

    There are a couple of means to remove air from circulating water - a high-hat that allows air to accumulate as it passes or accumulates at a high point. Once enough is there, it is released via a float valve. Or, something like an air scoop (Spirovent is one brand), that literally combs microbubbles out of the passing water. Sometimes, it works best to have both.

    Personally, I'd look at all of the radiators, baseboards, etc. and see if I could find any valve, joints, etc. that might be leaking. Note that circulators can introduce air into the system as well. Keeping in mind that it may only be sucked in, it might not be easy. I'd call someone as a last resort. Purging air is not that technical. As noted, with the system shut down, any poor joint might leak more when you turn it back on, so fixing it now might not make much difference and have to be done again. I'd probably consider waiting, but look carefully at the whole system and do maintenance.

    Make sure that the expansion tank is not waterlogged and the water makeup system is working properly. Also, while things are shut down, you could check the static pressure of the expansion tank, but you'd have to relieve the water pressure first, otherwise the air and water pressure would be the result of water, not the air in the tank.
  5. Barry J

    Barry J New Member

    Messages:
    99
    Location:
    Mass
    I was talking to my neighbor who works for the oil company, He said he would switch my air venting vavle to a , what I think he said was a "spiral Valve", I think that's what he called it, something with a "S". He said his cost was about $70-80, and works better than the usual valve. Do you know anything about this vavle???
    Thanks
    Barry
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
  7. Barry J

    Barry J New Member

    Messages:
    99
    Location:
    Mass
    Thanks alot...so definite worth the money???
    Think I should go with it??
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
    It works better than an air scoop. If you have leaky valves or joints somewhere, you still might get some air buildup. Note, sometimes a circulator can suck air in if the seal is wearing out. On the low-pressure side, it doesn't leak water out, but sucks air in. A Spirovent should definately help, though. If the air exhaust hole gets limed up or the float valve sticks, you can disassemble, soak in vinegar and return it to like new state. Instructions are on their website.

    A circulator often cannot push water up through an air pocket (not enough head pressure). Air accumulates at the high points. If you have a good extraction device, and the leak isn't too big, while the system is cycling (i.e., in the winter), it should be able to keep up and keep air from accumulating; the Spirovent has a SS brush in the water stream that literally combs microbubbles out of the water stream as it flows by. When enough air is captured, a float opens and allow it to vent out the top until the float recloses the valve. Hard to tell in the summer or late spring when the system doesn't run often. No circulation, no chance to extract air as it moves by.

    That's cheap to have someone install one...my guess is it would be more like double that if you were paying full price.
  9. Barry J

    Barry J New Member

    Messages:
    99
    Location:
    Mass
    Don't know if this is another indication of what may be my problem, but at times lately, when I go into the work shop..where the furnance is, I smell a faint smell of oil, that I did not notice before...not much and sometimes not at all, just once in awhile.
    Does that have anything to do with anything needing attention??/

    As for the price of the spirovent, it' my neighbor that works for the oil company, luckily he said he would help me do it, and get the part at his cost...must be refering to the Spirovent junior for around $80.
    Barry
  10. cattledog

    cattledog New Member

    Messages:
    42
    Location:
    Portland, Oregon
    Find the air leak

    Barry--

    Adding the spirovent to remove air will not get to the root of the problem. Air should not be in a closed system and can lead to corrosion of some components over time. You may be able to keep the gurgle noise down, but the circulating water will be saturated with air/oxygen. A closed hot water system should not require make up water.

    The system should be pressurized with an expansion tank and should not bring in air upon cooling like a steam system will.

    You should be looking for a leak of some sort, and I like the suggestion offered by jadnashua that the low pressure side of the pump could be at less than atmospheric pressure.

    What is the system pressure in the expansion tank? Are you pumping away from the expansion tank? If the tank pressure is too low, the circulating pressure drop high, and you are not pumping away you may be pulling in air. Most closed hot water systems are designed to run at 10-15psi.
  11. Barry J

    Barry J New Member

    Messages:
    99
    Location:
    Mass
    I don't have a pressure gauge on my expansion tank, but the gauge on the front of my furnance, reads at about 11-12psi
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
    That's probably just barely above the minimum pressure...any lower and the boiler might shut down with it's safety monitor.

    If you have an auto-fill valve, it may need adjusting. You should check the operator's manual to determine the proper value...it could be correct, but is likely on the low side.

    If you've got an accurate tire pressure gauge, you can verify that reading by putting the gauge on the fill valve of the expansion tank.

    If the boiler is now off for the season, it might go down a little because things are cool, but that is one purpose of the expansion tank, to keep things fairly constant.
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