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Hydronic boiler flow problem

jimmyenz17 Member Posts: 14
edited December 2023 in THE MAIN WALL
Hello all,
I have a hydronic boiler Utica 150; supplying
A) Baseboard Radiators in 2 rooms (with separate zone valve)
B) Radiant floor in one room
C) Indirect tank for DHW (80G)

I am pretty sure it is oversized at least 20-30%.

Problem I have is that the Baseboards in the rooms do not heat well at all especially during cold days. I believe it is related to flow (possibly undersized circulator pump? it is currently TACO 007).

For instance, if room temperature was 69F, if I raise the thermostat to 70F, it takes 2-3 hours for it to acheive it in one of the rooms (I got this from my Ecobee thermostat/Beestat).

Another instance (this is uncommon for me to set temp so high but in this instance I did):
Room temp initially 68,, when I raised to 72, then it took 8 hours to acheive it (outside temp was 28)
Lastly, the basement is very warm. There must be a lot of heat loss happening there (and unfortunately my pipes are not insulated yet, which I will work on later).

Here's what happens in the boiler during this time:
Boiler temp 160 --> runs for 5-7 min --> boiler temp now 180, and it shuts itself.
I can not hear circulator pump when the boiler is off but maybe it's quiet. and the cycle continues. Essentially every 15-20 minutes the boiler turns on when temp is 160, works for 5 min, acheives 180 and turns itself off.

I know the boiler is oversized, but I wonder, if a bigger circulator pump help with the short cycling and heating the baseboards faster?
I looked at some of the charts for circulator pump sizing, with my 150K BTU boiler, the GPM on the X-axis is between 15 to 25 GPM (using different sources). I have about 6 feet of header (for supply) for the near boiler piping. I have a hard time calculating the pressure drop for baseboard in the formula (I think it's 0.03 per ft?). My guess is on the Y-axis of the chart I have

The pressure head drop, I had a hard time calculating.

I guess my main question is if I go from Taco 007 to TAco 0011, could that help the issue?

An overall question, what is the main downside of possibly "oversizing" the circulator pump; does it significantly increases the wear/tear on the copper pipes or Pex?
appreciate your input.


  • jimmyenz17
    jimmyenz17 Member Posts: 14
    Here are some pics 

  • Ironman
    Ironman Member Posts: 7,342
    The pump is mounted incorrectly and is probably going bad.

    The 007 should be sufficient, but it must be mounted horizontally. 

    I’d replace the pump and mount it correctly. A Grundfos ups15-58 on medium speed is the equivalent of the 007 and would give you one higher speed if needed.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • jimmyenz17
    jimmyenz17 Member Posts: 14
    @Ironman , thank you! 
    I did flip it horizontally yesterday (parallel to thefloor). I did not get a new one, I’ll give it time and see if it’s salvageable. 
    Aside from symptoms of not heating well, is there another way of telling if circulator pump is functioning at its capacity? 

    I wonder if there is a formula that can measure flow capacity within pipes based on supply and return temperature difference ; maybe over a specific time from when the boiler turns on?
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,790
    How much radiation is connected? How many linear feet of baseboard and how many floor loops (and lengths if you have them)?
  • Jamie Hall
    Jamie Hall Member Posts: 22,899
    "I wonder if there is a formula that can measure flow capacity within pipes based on supply and return temperature difference ; maybe over a specific time from when the boiler turns on?"

    There isd, but you need to know the flow rate in gallons per minute. It is simply the flow rate, in gpm, times the temperature difference from supply to return, in Fahrenheit, times 500. That will give you BTUh.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 21,840
    Measure the temperature going into the baseboard and temperature coming out at the other end. Add them divide by two to get the AWT average water temperature.

    Then find the output chart for the baseboard you have or a similarly sized one.

    This chart shows some output example.

    The next riddle would be determining if there is enough baseboard in the rooms to cover the heat load. So a load calc is needed.

    Has it worked in the past?
    Is there a bypass on the boiler between supply and return? A few more boiler piping pics would help.

    If you change that circ, add a place to connect a gauge on either side to calc actual flow rate with this example.
    Or add a Caleffi Quicksetter :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 9,409
    Are you sure the circulator is running at all, that you're not just getting gravity flow?
  • mattmia2
    mattmia2 Member Posts: 9,409
    It could also be air bound. Do you get enough DHW?
  • Ironman
    Ironman Member Posts: 7,342

    Is this a mixing valve and is this the loop having trouble?

    If it is a mixing valve, it won’t work being piped that way.

    Some more pics for better clarity would help.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • jimmyenz17
    jimmyenz17 Member Posts: 14
    Thanks to all for your replies; just getting back to the thread for some updates.
    @Ironman ; thanks again, here is the image of corrected 007 orientation.
    -- I see improvement so I did not get a new one (the baseboards heat faster relative to before); and instead of 8 hours, it now takes 3-4 hours typically now in similar conditions as before.
    --And yes, there is a mixing valve for "radiant floor" loop, see comment below on that. it has its own pump in the basement in a panel near near the destination "room2", before it gets into the subfloor.

    @Hot_water_fan and @hot_rod

    Pipe length
    A) Boiler header = 5 ft
    B) Pipe to indirect = 2 ft
    C) Pipe to room1 baseboard= 115
    —room1 baseboard length is 40 ft.
    D) Pipe to room2 (radiant floor) =50 ft radiant floor.
    -this loop has a mixing valve at the radiator so about 120F water gets to it. This loop also has its own circulator by the way.
    E) Pipe to room3 baseboard = 60 ft.
    —room3 baseboard length is 40 ft

    When thermostat in room1 baseboard calls for thermostat, here are the pipe temperatures:
    On the boiler Supply (header) it is about 166-170 F
    On Pipe Supply to the room1 (near the boiler), it is about 164-166
    On the boiler Return , it is about 131-133 F

    @mattmia2 , I assume the circulator is working but I don't know how to determine if it is optimal for the system, I do get enough DHW in the 80G indirect tank, it hasn't been an issue.
    I am sure my boiler is very oversized (but not planning to change it anytime soon); in the future I may add more load (baseboards) when I finish the basement etc.

    In the meanwhile, I wonder if insulating all the pipes for different zones (radiant floor, room 1-3) will make a difference. Not sure if pex pipes are typically insulated out there.

    thanks again for being a great resource. Happy Holidays & Merry Christmas to you all
  • jimmyenz17
    jimmyenz17 Member Posts: 14

    EBEBRATT-Ed Member Posts: 15,304

    You can't assume the circulator is running when the boiler is shut off. You could be wired wrong. The fact that the room heats eventually shows it is probably not an air problem. When the boiler shuts down at 180 and the thermostat(s) are still calling for heat the circulator should still be running to take the heat out of the boiler and distribute it. When the temperature drops the boiler should restart and this will continue until the thermostat is satisfied.

    You can also safely raise the high limit setting to 190. It will only get to that temperature if it needs to to heat the load.

    Think about driving your car bumper up to a huge tree and pushing the gas pedal. You not going anywhere but your burning fuel.

    If your boiler limit is not high enough and your circulator may be shutting down with the boiler you will burn a lot of fuel and not get the job done.

    Your boiler output is 127000 btu (input of 150000) so you pump should move 12.7 gpm.

    The circ pump is capable of this if not restricted. Those Honeywell zone valve can be restrictive I have found out the hard way about it the hard way.
  • HomerJSmith
    HomerJSmith Member Posts: 2,391
    edited December 2023
    As a general note, There are several conditions that can create a low heat output, some of which have been mentioned. Insufficient pex loops in the slab or underfloor, loop embedded too low in the slab, no heat diffusion plates on underfloor pex, insufficient supply water temp, flow restrictions to the loops which could include high pressure losses which could be do to excessively long loops, valve that maybe partially closed, etc.
    Further diagnosis is warranted.
    As a further note, having a Spirovent so close the the input to the pump can suck air into the sys or at least create turbulence in the Spirovent. 10 to 12 diameters of straight pipe length before the pump inlet.
  • hot_rod
    hot_rod Member Posts: 21,840
    We have seen a number of sludged air separators here recently. Easy enough to split open the Spiro to see what is inside. Reducing flow has the same effect of having inadequate SWT.

    The best way to confirm actual output is shoot temperature at the baseboards, supply end and return end.

    Add the temperature then divide by 2 to get average AWT. Use that to see what the fins are actually putting into the room.

    Your pump and ZVs should be adequate to move the btu.

    Then expansion tank below the Spiro makes that assembly the PONPC, no way to suck air into the system, unless there is no pressure at all on the piping?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • FarmerBob
    FarmerBob Member Posts: 4
    Ironman said:

    The pump is mounted incorrectly and is probably going bad . . .

    . . . AND never with the label on the Cartridge "Upside Down!" Also make sure the system is flowing in the "correct direction". My problem, I think. A true "Gravity Fed" system only needs a little assist, if any at all. So the 007 should be OK.