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how do I measure overfire draft in Buderus 115ws3?

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alias2102
alias2102 Member Posts: 10
edited March 13 in Oil Heating
The boiler has a special port for this purpose. It is a brass nipple with a screw. Unscrewing it reveals a tiny pinhole. It is so small that no static tip fits through it. Another problem is boiler door insulation on the other side of the pinhole. I saw no hole on the other side of the boiler door when I opened it. Essentially, the pinhole is blocked.
How does one measure the overfire draft in Buderus?

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  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,840
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    It is in the instruction manual.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • SuperTech
    SuperTech Member Posts: 2,164
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    I usually just attach my probe to it with a piece of rubber tubing. A piece from my manometer or a piece of old pressure switch tubing will work.
  • alias2102
    alias2102 Member Posts: 10
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    Perhaps, these 2 photos illustrate the problem better. First one shows the pinhole next to the static tip. Pinhole diameter is barely 1/16 in. The other photo shows the other side of the port. There is no opening into the chamber. There is a small hole next to the viewport but it is not connected to the pressure port.
    I'm not sure how connecting a tube to the port with no opening into the chamber would help.




  • SuperTech
    SuperTech Member Posts: 2,164
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    In my experience all the Buderus boilers I've worked on have a port that you loosen a small brass plug with a small flathead screwdriver. I unscrew the plug a bit and slip the hose over the port and attach my Testo probe or a manometer to measure the draft. What you have pictured looks different from what I usually encounter. 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,529
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    Just take the fitting off an poke a small hole through the chamber material
    alias2102SuperTech
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,840
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    I would use one of those insulation support rods (commonly used as a search bit) in my cordless drill to make that opening communicate with the chamber, then attach one of these to the 1/8" or 1/4" female pipe thread
    Then attach the rubber hose from the draft measuring device to the barb side of the fitting.

    Or you could just open the glass sight door by removing it. You can certainly get a reading through the sight hole using the probe without removing the rubber tubing from it. Sometimes that boiler operates with a positive pressure, so wear heat resistant cloves like the fire fighters use.

    Working on heating equipment, your tool box should have those gloves. Also I had 3 different barb fittings in my combustion analyzer kit. 1/8" 1/4" and 3/8" by the 1/4" tubing size of my manometer, or draft gauge.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    alias2102
  • alias2102
    alias2102 Member Posts: 10
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    I just can't believe Germans would design a pressure port in such an odd way. There must be some trick to it. I have a gnawing suspicion that the port hole connects via a lateral door passage to the much bigger sight hole. I need to test this theory.
  • alias2102
    alias2102 Member Posts: 10
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    These Germans are a clever bunch. The pressure port does connect laterally to the sight hole (see the photo). It is angled. This design avoids measuring compounding effects of both static and velocity pressures when measured parallel to the flow.


  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
    edited March 14
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    The 115 is a three pass positive pressure boiler . You don't take measurements on the busness side . I believe that port is used on German controls , over there ...
    I have enough experience to know , that I dont know it all
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
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    The boiler is fire tuned , set the burner to spec , take your reading at the stack , I recommend a W nozzle with todays oil , The stack temperature needs to be adjusted through the setting of the baffles .. 350*-400* depending of venting ...
    I have enough experience to know , that I dont know it all
    SuperTech
  • HVACNUT
    HVACNUT Member Posts: 5,841
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    Big Ed_4 said:
    The 115 is a three pass positive pressure boiler . You don't take measurements on the busness side . I believe that port is used on German controls , over there ...
    Buderus wants 0 to slightly positive over fire on the G115. A piece of 3/8 vinyl hose on the analyzer makes do.
    When Buderus offered the G125BE in the States, you used a manometer at that port to check/set static pressure.
  • alias2102
    alias2102 Member Posts: 10
    edited March 22
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    I discovered that sticking a 1/8 " silicone tube into the port was a simple solution. It fits snuggly in the pressure port. It gave me +0.01 overfire, and the breach was at -0.02. The numbers comply with the Riello 40 F3 spec.