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Monoflo problem

SuperTech
SuperTech Member Posts: 1,856
I'm looking for some opinions from the community about a problem I came across today on a service call.  I was at an old house (built in 1797) that has a B&G monoflo system in it. The boiler has two space heating zones as well as a boilermate. One zone is fin tube baseboard, looks like it's all 3/4" piping in a series loop. The other zone is a1-1/4" monoflo loop with convectors. 

The problem is that the first convector doesn't heat properly. After 15 minutes of the thermostat calling it will only be lukewarm. Strangely enough the return side of the emitter begins to warm before the supply. There is a coin vent which is on the supply side of the convector but no air comes out when I open it, only water.  I couldn't access the main directly under the convector but I did notice that the rest of the convectors on the zone have monoflo tees on the supply and return sides. I thought this was strange because from I remember in Dan's books this was only necessary when the emitters are below the piping.  

I'm pretty sure this house wasn't always zoned. Zone valves are on the supply side of the boiler not far after the cast iron flow check.  The only thing that has changed recently since the current owners have been there (2 years) was a plumber replaced the zone valve on the monoflo zone. Originally the zone valve was 1" and he installed a 3/4" zone valve in its place for some reason.  So now it goes from 1-1/4" to 3/4" and back to 1-1/4" before the first convector which isn't heating properly.  I'm not sure if this would cause the problem.  The owners aren't sure if the convector worked properly last winter. 

So I'm kinda stumped. This wasn't the main reason for me being there, the indirect tank wasn't heating properly but that was a separate issue.  This was one of those "hey, while you are here can you take a look at this?" things. 

Any ideas or opinions would be greatly appreciated. 

Comments

  • Long Beach Ed
    Long Beach Ed Member Posts: 1,089
    Bigger radiators were often piped with Monoflo tees on both the supply and return. I would guess this radiator only has one and the others all have two. So the water is entering the return side and being sucked out of the supply by the Monoflow tee. There may be a big air bubble in the return side of the radiator which doesn't have a vent. Or the supply and return are piped too close together on the main.

    I can only speculate that reducing the size of the zone valve lowered the flow sufficiently to noticeably reduce flow to that cool radiator. A 3/4" zone valve in a 1-1/4" pipe? What's that about?

    Sometimes cranking up the supply pressure to a Monoflow loop for a few minutes will purge the air. Give it a try, but I'll bet that 3/4" zone valve is a big part of the problem too.
    SuperTech
  • Ironman
    Ironman Member Posts: 7,085
    Can you view the Tees below the convector to see how it’s piped?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,149
    The zone valve being too small is killing the flow in the Monoflo loop.

    I replaced a boiler last year that had a 1 1/4 Monoflo loop with Monoflo tees on the return only. Heat loss was about 50 K with fin tube baseboard to match and it always heated fine with a Taco 007 circ. But I added an indirect so I needed another zone.

    I use two Honeywell 1" zone valves. I forget the CV of the valves but they were like 4 or 5 cv. The Monoflow zone wouldn't heat well at all...very sluggish even with the indirect zone valve closed.

    I took out the Honeywell 1" zone valve and replaced it with a 1" Taco with like an 8-8.5 Cv

    Big difference it worked fine after that. Monoflow tees have a bit of resistance
    mattmia2SuperTechIronman
  • hot_rod
    hot_rod Member Posts: 18,254
    Ed is correct, it’s not the pipe side but the Cv of the valve to be aware of
    A 3/4, 1 and 1-1/4 zone valves could all have the same Cv, the same side opening, just the connection size changes

    While not my favorite, those boxy White Rogers 1361 have about the highest Cv, or full port ball valve type zone valves.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGrossSolid_Fuel_Man
  • clammy
    clammy Member Posts: 2,829
    From my experience when encountering mono flow system which baseboard zone have been added and zone valves installed for zoning . The mono flow side never seem to function as well as they did when it was just single pump . Personally I always just treat the mono flow as it was and install a pump strictly for it and if there baseboard loops then it’s another pump and zone valves . As other have said check the installed tees and see if there’s one or two mono flows installed and also check the space between them if to close ,flow will by pass the rad due to less pressure drop .the heat your feeling on the return side may just be thermal migration due to the radiator being cold or possibly due just wide temperature differences . The Replacement of the original larger zone valve w a small one is not helping anything ,and as pressure drops go if I was water I would certainly flow that baseboard loop over all those mono tees and radiator and radiator valves ?
    Food for thought peace and good luck clamm
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    SuperTech
  • SuperTech
    SuperTech Member Posts: 1,856
    Ironman said:
    Can you view the Tees below the convector to see how it’s piped?
    Unfortunately it would be extremely difficult to access the tees. The main runs into a very tight crawlspace that is probably only 18-24" high. It's full of cobwebs, debris and dead mice. I didn't even want to send my apprentice in there.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,149
    @SuperTech

    I would look at it like it probably worked at one time so look outside the crawl space for what has changed. Or maybe that's just me trying to avoid the dirt rocks broken glass and lack of light :) and mice . I 'll bet if you fix the flow it will start working.

    Monoflow tees depend on velocity and flow to work. If the flow in the monoflow main is low it can't pull water through the branch. Less pressure drop across the monoflow tees the less flow in the branch.

    Especially with 2 monoflows/rad you need the flow. If they sized the main for 1 1/4 they were probably expecting flow above 8 gpm which 1" maxes out at.

    The heat loss probably doesn't need that much flow but the main does. In the old day's oversized was the rule. And with double up monoflow tees it's probably old
    SuperTech
  • SuperTech
    SuperTech Member Posts: 1,856
    My first thought was that the 3/4" zone might be the problem as well. I figured that the system must have functioned correctly for years and the only that has changed recently was the zone valve. I have no idea why the plumber replaced the entire zone valve. It's a Honeywell and I know from experience that you can replace the guts of a 1" valve with the guts from a 3/4" valve without any problems. I suggested to the homeowner that he should call the plumber back to change the valve body back to 1". He asked me to do it, I didn't feel comfortable charging him for doing that repair when I wasn't confident that it would fix the problem.  

    There's probably 20' of 1-1/4" pipe between the zone valve and that first convector that isn't heating properly.  Why is it only affecting the first convector on the monoflo loop?

    I will try to raise the pressure and bleed the convector more when I go back just to make sure it's not air bound. I thought air might be the problem but remember reading in Dan's books that if you try to bleed a radiator and you don't get air out that you should stop because air isn't the problem.  But the coin vent being on the wrong side of the convector might be an issue.  Who knows, maybe the flow was originally going the opposite way on the original boiler. 

    Thanks again everyone for the feedback.  I love this site, it has been a huge help for me over the years in becoming a better technician.  Maybe one day I will actually be a super tech.
    STEVEusaPA
  • clammy
    clammy Member Posts: 2,829
    That coin vent on the wrong side could be it . I had a similar on a call and saw the vent was on the wrong side it was a convector w just unions so I open the boiler drain and while it was draining flipped it on the fly and that was it . It had been a issue for years and it end up being unable to get the air out ever. The customer was really happy it was the only convector that seemed to never get hot now it was working . That sound better then going in the crawl space .
    Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    SuperTech
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,149
    Coin vent on the wrong side? Maybe someone swapped the supply and return at the boiler is it possible they did that? Check the arrows on the monoflow tees you can see.
    SuperTech
  • Big Ed_4
    Big Ed_4 Member Posts: 2,075
    Did you check the butterfly valve on the riser ?
    I have enough experience to know , that I dont know it all
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,989
    So, prior to 2 years ago, the 1-1/4" diverter tee loop operated properly.

    Then:
    The only thing that has changed recently since the current owners have been there (2 years) was a plumber replaced the zone valve on the monoflo zone. Originally the zone valve was 1" and he installed a 3/4" zone valve in its place for some reason. So now it goes from 1-1/4" to 3/4" and back to 1-1/4" before the first convector which isn't heating properly.

    And you want an opinion on what the problem is.

    Let me remind you that @DanHolohan is very specific on how touchy diverter tee systems are with pressure drop. Then read this statement
    The only thing that has changed recently since the current owners have been there (2 years) was a plumber replaced the zone valve on the monoflo zone. Originally the zone valve was 1" and he installed a 3/4" zone valve in its place for some reason. So now it goes from 1-1/4" to 3/4" and back to 1-1/4" before the first convector which isn't heating properly.

    And then see if you can figure out what might be going on.

    Just a thought from a HeatingHelp Fan.

    Respectfully,
    Mr. Ed
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
    Long Beach Edmattmia2Solid_Fuel_ManSuperTech
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,542
    I would get the boiler hot, force that 3/4" valve open, and power purge the monoflo loop from the return at the boiler. This will get some flow going in the loop. Now, check that convector for heating. If it's hot, then you most definatly have a flow problem.....which is my vote as well.

    That is an easy to get flow through the 1.25" loop w/o changing anything. Then procede to make it right. My experience with monoflo is that each loop needs a dedicated and properly sized circulator. The mono tee's add a good amount of resistance to the loop and need flow to work. 

    I'd do that before going into a crawl space too!

    Is this an all copper system, or iron pipe/tee's or a mixture of both iron and copper? 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SuperTech
    SuperTech Member Posts: 1,856
    It's all copper. I should've checked the direction of the tees. At least now I have a plan to attack this problem.  It sounds like the popular opinion is that I should have gone with what I originally thought was the problem,  the zone valve that was changed. So I will offer to change it back to a 1" zone valve and raise the boiler pressure and try to purge the zone. If all else fails I will suggest flipping around the convector so the coin vent is on the return side. If the customer has me do this I'll update this thread with my results.  


    Thanks again everyone!
    Solid_Fuel_Man
  • pedmec
    pedmec Member Posts: 713
    If your going to open up the system and gain access to the monoflo tees I would add ball valves on the branches to the supply and return to the convector with purges on both sides. Purge thru both sides of the branches to the convector. I have found that you get air pockets in the piping that can't be removed at the coin vent. adding purge valves at both branches off the monoflo allows you to know that it definitely ain't an air problem. Of course this is only if you have access to the monoflo tees. I have had to do this to get the air out on some monoflo systems. Bleeding the convector at the coin vent without being able to isolate which side is venting is going to vent the side that is not air locked.

  • mattmia2
    mattmia2 Member Posts: 7,202
    It would be nice to know what the cv of the old valve was. You should look at cv rather than pipe size. I know some of the taco zone sentry valves have high cv for their size.
  • hot_rod
    hot_rod Member Posts: 18,254
    The common spring return valves Erie, Honeywell, Caleffi, etc will be 7.5- 8 Cv. Unless a supplier specifically orders low Cv valves.

    The orifice, or port in the valve will be about the same size regardless of the pipe size in the valves.

    Here is a 3/4 next to a 1-1/4, 7.5 Cv.

    So changing the body doesn't change pressure drop. Unless the 3/4 valve was a 2, 3 or 5 Cv?

    Very finicky piping dynamics in one pipe systems. They don't take kindly to changes.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterManSolid_Fuel_Man
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,989
    edited December 2022
    @hot_rod ...Is that an Optical Delusion? OR is the opening on the larger pipe diameter valve actually smaller?

    Rhetorical Question Bob
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • hot_rod
    hot_rod Member Posts: 18,254

    @hot_rod ...Is that an Optical Delusion? OR is the opening on the larger pipe diameter valve actually smaller?

    Rhetorical Question Bob

    Good eye!

    Two things, the smaller is an Erie, the 1-1/4 is a Caleffi. Also looking at them from different directions. But gauging them on inlet side, there is only a few thousands difference.

    Here are two Caleffi, 3/4 fip and 1-1/4' sweat.

    So a guy, or two guys, or a guy and a gal, or two gals, could argue that the smaller body with a bell reducer (increaser) would be a smoother transition.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,542
    I'd get rid of the zone valve and put a circulator in. Generally a 0010 (or equivalent in red) for 1.25" monoflo loop. Sometimes a 007 (or equivalent in red) will suffice if there aren't many monoflo Tee's in the total loop. Pump away, into the loop for best results. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!