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Help needed - constant air in hydronic loop in 1950s house.

ptz3233ptz3233 Member Posts: 6
edited November 19 in THE MAIN WALL
Hi all, thanks for your time.
About a year ago I bought a fixer-upper 1950s house in the northeast.
I have cast iron rads in the 1st and 2nd floors, and copper with fin baseboard in the basement.

1st and 2nd floors are on one loop, basement is on another. I've only ever turned the basement loop on twice, to test.

When I was fixing up the house, I had a plumber replace the original 1950s boiler with a new one.
Ever since moving in, I have not been able to eradicate the noise of gurgling and bubbling in the pipes.
It gets way worse as it gets colder and the boiler works harder.
I have bled every radiator many many times, I only ever get a clear stream of water. Even after bleeding multiple gallons at a time, the air persists.

I have also purged the loop with the purge outlet the plumber installed.
One thing I noticed is that the system seems to be running in reverse, have old style monoflo tees under the rads in the basement, and according to the marking on those tees, the water direction is wrong. I'm not sure wether this is an issue or not, the system has no problem heating the house, it can just get very loud with all the gurgling.


My circ pump is on the return under both of the zone valves, and above the pump and below the zone valves is an automatic air vent. The cap is screwed on loosely. I suspect the placement of this air vent may be allowing it to suck in air when the pump runs hard, but I cant confirm this. I have closed the cap on that and let the boiler sit with the pump and heat off to see if I could get the air to rise to the top floor but still see a clear stream of water. The only thing that could be a clue is that the water seems "fizzy" when bleeding at the top floor bathroom rad, it seems this rad receives the most pressure.

I'm wary to keep bleeding and purging, as I know the older the water the better, and new water could start corroding the old cast iron rads, and introduce its own microbubbles.

Any help would be appreciated - this noise is driving me absolutely crazy (Im sure some of you can relate)

Comments

  • EdTheHeaterManEdTheHeaterMan Member Posts: 1,046
    edited November 19
    The new boiler's near boiler piping is at fault, I'm sure. send pictures of the boiler piping from several angles so we can see how the pipes enter and leave the boiler.

    Mono-flo in reverse may add to the problem

    This publication will be helpful in describing your problem to the installing contractor.

    read page 9, Zoning with circulators (First a Word on "Pumping Away")
    https://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2020/01/FH-Z100B-BG-Zoning-Made-Easy-2.pdf

    For future help with problem-solving, see if you have any pictures of the old system, maybe from an inspection when you purchased the home. This will help in proving the boiler was installed incorrectly. the old system may have had an air removal or air management device in the system
  • ptz3233ptz3233 Member Posts: 6











    The new boiler's near boiler piping is at fault, I'm sure. send pictures of the boiler piping from several angles so we can see how the pipes enter and leave the boiler.

    Mono-flo in reverse may add to the problem

    This publication will be helpful in describing your problem to the installing contractor.

    read page 9, Zoning with circulators (First a Word on "Pumping Away")
    https://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2020/01/FH-Z100B-BG-Zoning-Made-Easy-2.pdf

    For future help with problem-solving, see if you have any pictures of the old system, maybe from an inspection when you purchased the home. This will help in proving the boiler was installed incorrectly. the old system may have had an air removal or air management device in the system

    EdTheHeaterMan, Thanks for your reply. I have attached many pictures of the piping around the boiler, and a picture of one of my monoflo tees. Reading that brochure definitely makes it seem like the circ should be on the supply. I do wonder if thats the "full" problem however.
  • CanuckerCanucker Member Posts: 635
    Your air vent pictured in the second last pic is almost useless in that position. It would be a good spot to connect the expansion tank though. Currently there is no reason for the air to travel up that pipe to the vent
    You can have it good, fast or cheap. Pick two
  • ptz3233ptz3233 Member Posts: 6
    edited November 19
    Canucker said:

    Your air vent pictured in the second last pic is almost useless in that position. It would be a good spot to connect the expansion tank though. Currently there is no reason for the air to travel up that pipe to the vent

    Thanks for your reply - where do you think a better place for the air vent would be? Im guessing on the supply side

    I was able to find a picture of the old boiler, it does not seem to be clear enough to tell what is really going on however.

  • CanuckerCanucker Member Posts: 635
    @ptz3233 they make scoops for vertical pipes and yes, it should be on a spot where the hottest water passes through it. This is an example
    https://www.caleffi.com/usa/en-us/catalogue/discalr-air-separators-vertical-or-horizontal-pipes-brass-551705a
    You can have it good, fast or cheap. Pick two
  • SuperTechSuperTech Member Posts: 1,476
    edited November 19
    Looking at your boiler pictures,  it reminds me of the way I found the boiler piping in my home done. The boiler has a 1-1/4" supply that runs down the middle of the house to a wye, then it splits off to 1" copper pipes that feed the cast iron baseboards in a reverse return setup. Two 1" pipes return to the boiler.  
    I was quite surprised to find out that the venturi tees were facing the wrong direction. I'm thinking that it was a split loop monoflo design that may have been changed to two pipe reverse return at some point. When that happened or when the guys installed the current boiler they may have changed the supply direction.  

    Now its primary secondary, I've tried circulating both ways, it doesn't matter. The venturis cause a pressure drop and flow either way. 
  • IronmanIronman Member Posts: 5,922
    edited November 20
    Get rid of the auto vent: it's worthless in that place. Connect the expansion tank to the Tee above the pump where the vent now is. It can mount in any position. Set the fill valve and the air pressure on the tank to 15 psi. You have to do the tank air pressure with no water pressure on it. When you have it disconnected would be a good time.

    You could put a vertical MBR (air separator) on the supply out of the boiler if you wish, but it's really not necessary since any air that it doesn't catch on the first pass will go to the top of the cast ion rad's and have to bled manually. Standing CI rad's are the best air separator ever invented.

    Do these things and your problem will be gone.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,544
    The mono flow tee you took the picture of. Which way is the water flow in the main? With the arrow or against it? Also the branch pipe coming off that mono flow tee is it connected to the radiator supply or return?

    BTW I have seen mono flow tees with arrows pointing in both directions. One arrow used if you mounted the tee on the radiator supply pipe and the other when it is used on the return
  • ptz3233ptz3233 Member Posts: 6

    The mono flow tee you took the picture of. Which way is the water flow in the main? With the arrow or against it? Also the branch pipe coming off that mono flow tee is it connected to the radiator supply or return?

    BTW I have seen mono flow tees with arrows pointing in both directions. One arrow used if you mounted the tee on the radiator supply pipe and the other when it is used on the return

    The arrow is going opposite the direction of flow, and it seems the tee is connected to the return of the rad.

    I have actually seemed to have success with purging the system completely and running it both while keeping the autovent closed. This may confirm my suspicion that it was sucking air into the system in the position it's in.

    Moving the expansion tank will probably be the next thing I try, this may have to wait for the spring though. A wise man has told me that if the house is warm then don't go taking apart the boiler in the winter...
    MaxMercy
  • MaxMercyMaxMercy Member Posts: 73
    ptz3233 said:

    A wise man has told me that if the house is warm then don't go taking apart the boiler in the winter...

    Amazing how things that are so obviously logical, like not taking apart a working boiler in the winter or not jumping out of a good airplane etc. get ignored..



  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,544
    @ptz3233
    agree with not disturbing things in the winter if you don't have to.

    Did someone reverse the supply and return connections at the boiler??
  • ptz3233ptz3233 Member Posts: 6

    @ptz3233
    agree with not disturbing things in the winter if you don't have to.

    Did someone reverse the supply and return connections at the boiler??

    It looks like that was the case, I'm guessing my plumber did that. But it could've been a plumber before I owned the house who had it that way on the old boiler too.
    To see the direction of the tees I had to scratch off a few layers of old paint.

    From what I remember before I started working on the house, the boiler was original, and looks like a second loop was added when the basement was finished, and there was a circ per loop.

  • hot_rodhot_rod Member Posts: 14,075
    Yes it is quite possible to pull air into an auto vent, lock down the cap or remove that Amtrol vent.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • EdTheHeaterManEdTheHeaterMan Member Posts: 1,046
    On a monoflo tee, the preferred connection is to put the tee on the return of the radiator (or emitter) and make the water flow in the direction of the arrow.

    The opposite will also work. place the tee on the supply and make the water flow in the opposite direction.

    My guess is the air vent at the location so close to the intel of the circulator pump will allow the pressure to get low enough for air to enter the vent. one point to consider is that every pressure change happens over time. the outlet of the pump increase in pressure and the inlet of the pump decrease in pressure happens immediately upon the start of the pump. It takes time to equalize throughout the system. Only a second or so, but it does take time. In that initial shock of the startup, the pressure may drop below 0 PSIg for that split second.

    You can actually see this phenomenon can be witnessed if you have a gauge on the system. when the pump starts, you will see the gauge move past the operating pressure on startup, then quickly bounce back to the operating pressure

    During the surge, air will be allowed to go into the system on every start-up of the pump thru the air vent. That air is then distributed throughout the piping and make the annoying noise you are experiencing. Get rid of the air vent. if you have bleeders on the radiators, let the air out at the radiator bleeder location.

    This will add less air than trying to flush or purge the air out at the boiler.



  • EdTheHeaterManEdTheHeaterMan Member Posts: 1,046
    In looking at the old system, there was a path for air to leave the system and find its way to the expansion tank. see the parts indicated in the attached picture


    There is another point of concern. The 1" zone valve will only allow about 4.5 to 5 gallons per minute (GPM) to flow in the 1" pipe. This is due to the restrictions to flow designed into the valve. When the system was zoned by circulators, the flow rate could be as much as 8 GPM. As long as your system does not require more than about 45,000 BTU of heating capacity in that zone, there will be no problem. If however, the zone requires 60,000 0r 70,000 BTUs on the cold days, you may notice a reduction in the ability to heat the zone, This will show up in the radiators furthest from the boiler supply pipe.

    You may want to keep detailed records of the air noise and the temperature during the colder days (or nights, when it is colder) Get yourself an accurate thermometer and record the individual room temperatures and compare it to the thermostat set point. If it is consistently the correct temperature during the mild weather and the room temperatures begin to become noticeably cooler during the extreme temperatures, you will be wise to have these records. Record the outdoor temperature each time you record the indoor temperatures.

    Other than the obvious design flaws, the job looks like he did a good job. Craftsmanship I would give him an A Design is would give him a C-. Reading the instructions I would give him an F


  • ptz3233ptz3233 Member Posts: 6

    In looking at the old system, there was a path for air to leave the system and find its way to the expansion tank. see the parts indicated in the attached picture


    There is another point of concern. The 1" zone valve will only allow about 4.5 to 5 gallons per minute (GPM) to flow in the 1" pipe. This is due to the restrictions to flow designed into the valve. When the system was zoned by circulators, the flow rate could be as much as 8 GPM. As long as your system does not require more than about 45,000 BTU of heating capacity in that zone, there will be no problem. If however, the zone requires 60,000 0r 70,000 BTUs on the cold days, you may notice a reduction in the ability to heat the zone, This will show up in the radiators furthest from the boiler supply pipe.

    You may want to keep detailed records of the air noise and the temperature during the colder days (or nights, when it is colder) Get yourself an accurate thermometer and record the individual room temperatures and compare it to the thermostat set point. If it is consistently the correct temperature during the mild weather and the room temperatures begin to become noticeably cooler during the extreme temperatures, you will be wise to have these records. Record the outdoor temperature each time you record the indoor temperatures.

    Other than the obvious design flaws, the job looks like he did a good job. Craftsmanship I would give him an A Design is would give him a C-. Reading the instructions I would give him an F


    Thanks for all your insight, this is starting to make more sense to me. I purchased a copy of Dan Halohans book to educate myself some more. I am still crossing my fingers because I have not heard any air since closing the air vent.

    The true test will still be when the extreme cold comes in the next few months. This system was installed last year, but I was not living in the house at that time because of the renovations. It was kept at 55ish all last winter.

    Im not hearing any air in the pipes but I have a feeling there still is some at the rads, I think the problem may be that because the system is in reverse the bleeders are on the supply side of the radiators, but that may not matter.
  • hot_rodhot_rod Member Posts: 14,075
    @EdTheHeaterMan zone valve restriction?
    Most 3/4 and 1" ZVs are 7.5- 8 Cv.
    The large the WR are 11- 13. That really should not reduce flow as long as the circ can overcome a 1 psi drop at 8 gpm?

    Unless someone installed a 1 or 2 Cv zone valve, by mistake :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me

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