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Buderus G115 Breech Draft Spec

CFooteCFoote Member Posts: 11

I own a raised ranch in CT with a Buderus G115 w/Riello burner. It's a great unit and serves me well.

In reviewing specs in the installation manual, Buderus states, "After starting the burner, set breeching draft to -0.01 to -0.02 inches WC using a draft gauge.".

My service company is currently reading -0.043 draft, which he says is great because the exhaust gases are moving up the pipe faster and I won't have as much of a smell in the basement.

Can anyone explain why Buderus calls for the -0.01 to -0.02 spec? What issues does having a higher negative breech draft cause?

Thanks for your time.



  • STEVEusaPASTEVEusaPA Member Posts: 4,729
    edited August 2018
    Your tech is misinformed. Normally -.043 would be a good breech draft number, but not for the Riello, and not for this Buderus.
    Usually you set the draft over the fire first, and whatever is at the breech is just what it is.
    The more important reading is over the fire. Buderus and other newer boilers (3 pass) want (need) a positive over fire draft.
    Now with an MPO, for example, there is a test port and Burnham wants 0 to -.01, but it also tells you that the draft over the fire needs to be (for example) +.02 - +.035.
    Have him bring the manual (if you don't have it there) and reset your burner correctly.

    A higher draft wastes fuel, makes your stack temperature increase, pulls more air (excess air) thru the burner and combustion chamber for lower efficiencies.

    What were the rest of the combustion numbers?

    Edit: Looking at an online set-up guide (may not be an exact match) it states the breech can be 0 to -.03 with the over fire being 0 to slightly positive. So the over fire number is important, as well as the other combustion numbers.
    rick in Alaska
  • CFooteCFoote Member Posts: 11
    Thanks Steve for the fast response.

    Here is the printout - ignore the date/time

  • HVACNUTHVACNUT Member Posts: 3,699
    Ask him (or the company) why there's no stack temperature readings. Gross and net. It also doesn't state combustion efficiency.
    Oxygen is a little high. CO2 is a little low, and excess air really shouldn't be more than 25-30%.
    I like to see 0 PPM CO.
    How long did he leave the probe in the stack?
    Is there a draft regulator so draft can be adjusted?
    Did he do a smoke test?
  • STEVEusaPASTEVEusaPA Member Posts: 4,729
    ^^^What he said...
    After steady state, if you adjust that draft properly, then get true zero smoke, you can dial that Riello in much better.
    Considering all the missing numbers and the way off date, I'd be suspect of that analyzer's proper functioning/calibration.
  • CFooteCFoote Member Posts: 11
    Thank you both for your responses, he did mention his probe needed to be sent in as the temperature sensor was broken. I believe that left the tool with insufficient data to get combustion efficiency? I know, I rolled my eyes too.

    He has done a smoke test in the past, but not today, interestingly enough.

    There is in fact a draft regulator installed, about halfway up the stack (see picture). Is it really as simple as adjusting the weighted knob to adjust the breech draft?

    Thanks again guys - I really appreciate helping this homeowner out. This isn't cheap equipment, and I want it working as best as it can.


  • STEVEusaPASTEVEusaPA Member Posts: 4,729
    edited September 2018
    Yes it's that simple, but the draft needs to be checked over the fire with a proper working analyzer (or draft gauge). The fact that some of the analyzer isn't working properly means to me that none of the numbers could be trusted.
    I would put the regulator on the horizontal flue going thru the wall (move the weight to the proper side) so it mimics the vacuum breaker (looks like a damper) on the combustion intake pipe.
    Yes he should've done a proper smoke test.
    I would like to see a longer pipe length for combustion air, even if it means going all the way up to the ceiling, then down to warm up combustion air especially during the coldest days of the year. Cold air is not good for clean combustion.
    Other than that, and not pumping away (I see the circ on the return) everything else I can see in the picture looks pretty nice.
  • CFooteCFoote Member Posts: 11
    edited September 2018
    Got it Steve, thanks again for all the help in educating me.

    Would adjusting the intake breaker/damper to open more in the winter be beneficial for a quick fix while we re-pipe it?

    Just a follow-up picture - does the circ appear to be on the return? Isn't the return the pipe in the background?

    Hope you are having a nice long weekend.


  • STEVEusaPASTEVEusaPA Member Posts: 4,729
    Would adjusting the intake breaker/damper to open more in the winter be beneficial for a quick fix while we re-pipe it?

    That's not the proper way to use it. That vacuum breaker is two-fold.
    To provide combustion air if the intake to the exterior gets blocked, and a visual alert that the intake to the exterior is blocked/restricted.
    To me, the fact the combustion air intake is there in the first place, and it looks like the boiler is in a small confined space tells me it's needed. I would recommend extending the length- put a 90 up to ceiling, 2-90's and bring it back down to the burner. I'd think it could be modified in a 1/2 hour. Not pretty, but better for combustion.

    Just a follow-up picture - does the circ appear to be on the return? Isn't the return the pipe in the background?

    Hard to tell which is which.
  • CFooteCFoote Member Posts: 11
    Thanks a lot Steve for all the comments, I have some good ammunition to go back and get all of this squared away. I will follow up when its all completed!
  • Big Ed_4Big Ed_4 Member Posts: 1,572
    Positive pressure horizontal boiler ,love the avalable low firing rates .Go by the design fire , you can't go wrong... Great high 80%
    I have enough experience to know , that I dont know it all
  • Bob HarperBob Harper Member Posts: 856
    Agree with advice from Steve. On the smoke pipe, you cannot wrap with tape or insulation. It hides corrosion and prevents inspection/ cleaning. You need a cleanout in the base of the chimney and probably a listed liner. The connector cannot be cemented into the wall like that anymore. It is a connector and thus cannot be covered. It can go into a thimble where it can easily be pulled for inspection or service. You can tweak that burner a little further dropping the O2 as long as the CO remains below 100ppm. You want that barometric damper where you can inspect and adjust it easily. You should have some sort of strap or support on that offset in the smoke pipe.
  • CFooteCFoote Member Posts: 11
    edited September 2018
    Still working on this! Before I fixed the breech draft to the proper spec and attach a final combustion analysis on this thread, I have a quick question.

    The Buderus manual status breech draft should be -0.01 to -0.02...The Riello burner manual states -0.03 and that is finding my model # in a table Riello provides. Which manual should I pay attention to? My town inspector is saying the Riello.


  • HVACNUTHVACNUT Member Posts: 3,699
    I've always followed the Buderus specs.
    You'll notice that's not the only difference in the "initial setup" between the two. Only an analyzer can get you where you need to be.
    Theres not a world of difference between the two but if you see the flame rising towards the top of the chamber, it's too much draft.
    If your combustion numbers are good and a 0 smoke, don't worry about a .01 diff.
  • CFooteCFoote Member Posts: 11
    OK folks, here is round 1 of full analysis...

  • STEVEusaPASTEVEusaPA Member Posts: 4,729
    edited September 2018
    The date is wrong on the analyzer. It bothers me because a time stamp can be considered evidence in a legal dispute. If i had to go to court to defend that test, and couldn't tell you what day I did the test, it could damage credibility.

    Seems like you may be a little underfired/a little too much combustion air. Was a proper smoke test performed?
    What nozzle/pump pressure?
    I'd like to see a c/a, when the ambient air is 30 degrees.
    If the draft measurement is at the breech, you're good there.
  • CFooteCFoote Member Posts: 11
    Thanks Steve for the fast response.

    The opening where we stuck the analyzer probe was a good 1/3" opening, do you think O2 is sneaking into the pipe when we do this test? I can try re-sealing it and seeing if that makes any difference on the O2 %.

    Unsure of pump pressure, but we're using a 5560 nozzle (.55gph 60 degree spray). I believe we tried the next size up a few years ago and the Buderus was really making quite a noise when she initially fired up.

    I agree on another c/a with lower ambient air temp. That will also affect the draft I would think. We are supposed to drop into the 40s Saturday night, we'll see.

  • Robert O'BrienRobert O'Brien Member Posts: 3,251
    Stack temp is too high. EA is too high, should be around 30%. As you reduce air, the stack temp will drop. Stack temp should be in 350F range
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  • CFooteCFoote Member Posts: 11
    edited September 2018
    Thanks very much for replying Robert.

    I just checked the air gate setting on the burner itself and it is set for 3.5 as advised by the specific Buderus boiler (G115WS/3). The turbulator is a reverse disk on this model and I don't believe it's adjustable.

    Do you think I should adjust the air gate? I would add that the temps here (ambient air) are still quite high, around 60-70 degrees.

  • STEVEusaPASTEVEusaPA Member Posts: 4,729
    You don't want to adjust the air gate without taking a smoke test, and using the analyzer.
  • rick in Alaskarick in Alaska Member Posts: 1,149
    Also, check the nozzle type. Riello likes to burn best with a "W" nozzle in them. It might help your numbers.
    From what I can see, your pump is on the supply side, so you are ok there.
  • HVACNUTHVACNUT Member Posts: 3,699
    The Buderus/Riello specs are only starting points. The analyzer and smoke test is a must.
    Most OEM Riello set up specs are real generous with the air setting.
    You can definitely adjust the assembly depth. 5/16 nut driver and a flat head. The first notch is '0' not '1'.
    The higher the number, the more air goes through the turbulator rather than around it.
    But the tech should know all that already.
  • CFooteCFoote Member Posts: 11
    Hey Everyone,

    Still working on this as time allows with my friend.

    First, a couple of things. Before adjusting anything air related, we did do a smoke test. There was a small trace of smoke, so that is good. We used a Bacarach smoke tester.

    Next up, we tried to get Excess Air down into the low 30s. Adjusted the Turbulator screw down to 2 (was at 3). Interestingly, the Buderus specific manual from Riello does not mention a turbulator setting other than to say the turbulator disk is reversed.

    Anyway, now that the Turbulator was at 2, we dropped the air gate from the factory 3.5 to 3.

    We then ran a combusion analysis and adjusted the breech draft a little more, to get it in spec with the -0.01 to -0.02 Buderus wants.

    As you can see, we got Excess Air down, CO2 % is a little up, O2 is down, which is all to be expected (my understanding) with less air coming in.

    But still, we continue to have high stack temps - it is down from 480ish now to 455ish max. Still too high.

    Is it time to check the Baffles?


  • HVACNUTHVACNUT Member Posts: 3,699
    If stack temp is gross, and ambient is truly 80°, then a 360° net is good as long as that's at steady state.
    Which Buderus G115/?
    Riello BF?
    IMO, it can be dialed in a little better for 0 PPM CO, and a true 0 smoke.
  • CFooteCFoote Member Posts: 11
    Yes sir, that stack temp is gross. Furnace was running a good 15-20 minutes when this c/a was taken.

    Ambient is 80 in the furnace room, BUT there's a fresh air intake. Temps last night were 35ish when we did this test. My guess is there is a mix of cold and warm air, so perhaps 50ish degree air?

    I would like to have him get a remote sensor to put into the cold air intake, I think that would be helpful.

    It's a G115WS/3. Riello Series 40 F3.

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