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how underfired is too underfired and how to be sure piping is the cause

snugonesnugone Posts: 22Member
Bought a house two months back and it came with a Weil-Mclain HE-5 series 3 propane boiler with an a.g.a input of 133k BTU/hr. Even when the tank is full, on a day with a temperature above freezing, the inlet pressure to the boiler's gas valve sits at 9.1 inWC when operating. The manufacturer's stated range for inlet pressure is a minimum of 11 and 13 max. The manifold pressure sits at 8.6 inWC, and should be 10. I don't think that the white-rogers 36c74 is designed to lower the pressure reduction any less than the 0.5 it already is, and I obviously do not wish to crank on the adjument screw to find out.

The 120 gallon tank's regulator is a non-adjustable Fisher Controls R232-BBF, which I don't believe is the issue (although I have not attempted to check the line pressure at the tank end while under load).

My money is on the piping as the cause, but I assume there's some math involved to know for certain. The boiler is the only appliance on the tank, and the piping consists of 6 feet of 21mm outer-diameter black pipe at the boiler end (am assuming SCH 40 1/2"), and 20 feet of 15mm outer-diameter copper tubing back to the tank (am assuming 1/2"), making many sharp bends along the way.

My assumption is that this boiler has been operating this way since it was installed (back in the 1980's?). The air being non-adjustable, manifold pressure would seem to be fairly important. But just how off is off enough to be worried about? A combustion test at the outside vent gave these readings:
O2 11.5%
stack 260F
EA 110%
CO2 6.2%

Comments

  • aceboileraceboiler Posts: 14Member
    You could measure the radiators and see if the boiler is over sized?
    I think the HE units are hot Surface Ignition. If it is over sized for the radiators, then under fired might be okay? If its over sized and over fired they go through a lot of igniters.
    I always want to make sure the chimney doesn't condense, so you have to watch that temp for sure.
    Years ago when I started finding that the boilers were too big for the houses I would drop the gas pressure 1 inch on the manifold. Was told by the factory that was safe to do?
    Does the system have multiple zones? I have had to put zones together to keep the boiler from short cycling.
    Carbon monoxide needs to be tested before you do anything?

  • ZmanZman Posts: 4,868Member
    What is the static gas pressure with nothing on? This would be helpful in determining if pipe sizing is an issue.
    Is it possible to test combustion right after the boiler? You may be getting a diluted reading. Is a draft hood or damper installed?
    Definitely measure CO.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • snugonesnugone Posts: 22Member
    Zman said:

    What is the static gas pressure with nothing on? This would be helpful in determining if pipe sizing is an issue.
    Is it possible to test combustion right after the boiler? You may be getting a diluted reading. Is a draft hood or damper installed?
    Definitely measure CO.

    I recall seeing a static pressure of around 12 at the inlet before the valve activated. I will take a combustion reading closer to the unit. The venting is double wall duraconnect right from the unit and I was hesitant to drill into that, but since that time I've come to believe it's not a significant issue.
  • snugonesnugone Posts: 22Member
    aceboiler said:

    You could measure the radiators and see if the boiler is over sized?
    I think the HE units are hot Surface Ignition. If it is over sized for the radiators, then under fired might be okay? If its over sized and over fired they go through a lot of igniters.
    I always want to make sure the chimney doesn't condense, so you have to watch that temp for sure.
    Years ago when I started finding that the boilers were too big for the houses I would drop the gas pressure 1 inch on the manifold. Was told by the factory that was safe to do?
    Does the system have multiple zones? I have had to put zones together to keep the boiler from short cycling.
    Carbon monoxide needs to be tested before you do anything?

    Without doing the math, I'm certain it's rather oversized for this small house. In general that seems to be a common thing in this region. Yes, it's HSI. The only major non-original part appear to be the control (W-R 50d47 looks to have been replaced with a Honeywell s8910u). The system has 4 zones (if you include the indirect water tank), and incidently someone put in a tiny Extrol tank that's obviously too small and makes the relief valve piddle when more than 1 zone is receiving heat.
  • ZmanZman Posts: 4,868Member
    The regulator looks to be big enough, assuming you don't have other large loads. Tell us about the pipe sizing and length? Other appliances?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • snugonesnugone Posts: 22Member
    Regarding the CO measurement, which I too would like to know.
    My meter is a SOX3 which isn't capable of measuring CO, so in
    the meantime all I can do is to try and take a more accurate combustion reading (I'll have that new combustion reading done and posted in the morning.)
  • snugonesnugone Posts: 22Member
    Zman said:

    The regulator looks to be big enough, assuming you don't have other large loads. Tell us about the pipe sizing and length? Other appliances?

    The boiler is the only appliance on the tank, and the piping consists of 6 feet of 21mm outer-diameter black pipe at the boiler end (am assuming SCH 40 1/2"), and 20 feet of 15mm outer-diameter copper tubing back to the tank (am assuming 1/2"), making many sharp bends along the way.
  • aceboileraceboiler Posts: 14Member
    I guess i would buy an igniter and have it on hand. Maybe clean the sections. Save some money up for 10-20 years and then replace with some super high efficient unit............
    I have one of these i think 180,000 or so? I did the math on the convectors at about 120,000. Has three zones. I serviced it for about seven years now. Replaced the igniter once. I have four burners pulled and the orifice taps plugged. Still short cycles,
    (not nearly as bad). Chimney temps are as low as I dare go. I lined the chimney before i pulled burners.
    The company that installed it would come out every other year and replace the igniter.
    That's why they called someone else.
  • ZmanZman Posts: 4,868Member
    edited December 2018
    Your piping is undersized, probably about a 2" drop just for the pipe plus everything else. The question is, does it run OK? You will find out with combustion analysis.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • JUGHNEJUGHNE Posts: 5,653Member
    All LP installs around here have 2 regulators.
    (2 stage regulation)
    The little red one at the tank that delivers about 10 PSI.
    Then the green one at the house that drops it to 12-13"WC.
    This has been very helpful for cold weather applications, and puts a constant supply into the house.
  • captaincocaptainco Posts: 424Member
    Based on your O2 and flue temperature your efficiency is between 60% to 65% at the most
  • snugonesnugone Posts: 22Member
    Put a 5/16 hole 16" up the straight pipe that's coming off the elbow that's directly connected to the unit. That should be close enough to the unit and far enough from the elbow to avoid turbulance I think. No damper to deal with since the venting just turns again 5 feet above and exits to the outside through the wall.

    This mornings's reading, taken at the new hole:
    O2 11.5%
    309F
    EA 111%
    Co2 6.2%

    So other than the stack temp, results look similar.
  • snugonesnugone Posts: 22Member
    I've decided I don't want to think about re-piping the gas line before this heating season is over with.

    Today I tried replacing orifice fittings one at a time with plugs, and honestly was surprised how little the inlet pressure increased with each plug added. The most I plugged were 3 of the 8 total burners, which resulted in an inlet pressure of 9.4 and manifold pressure of 9.0.. and the healthiest looking pale blue flame I'd seen the unit ever produce despite pressures still below spec. I took combustion readings, though of course with so many burners disabled I imagine the stack was diluted with room air pulled in by the blower so the readings may be meaningless.
    o2 15.7%
    co2 3.4%
    ea 270%
    stack 275F

    Now, until I know the CO I'm not going to run it that way, and have reduced it to having only a single burner disabled.

    Thank you all for the information and advice, not to mention doing the calculations. Even if I didn't reply directly I've been taking notes; eg. having a spare igniter around makes a great deal of sense to me.
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