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Buderus- Chimney Condensation problems

TOM1124TOM1124 Member Posts: 5
Hello everyone I have been having an ongoing chimney condensation problem for the past year or so. I live on the south shore of long island. In January of 2010, I had a buderus g124 boiler installed and buderus logano hot water tank. Approx 85% efficiency. The following winter I noticed condensation dripping out of the chimney cleanout. I then had a 6" ss chimney liner installed by a reputable chimney company and was told that it will correct the problem. Earlier this winter i noticed the condensation was coming out of the cleanout again. I called my plumber, chimney guy, and buderus tech. They came to my house and inspected the boiler and it found to have correct btus, temps, etc. Buderus Tech and Plumber recommended that the chimney liner had to be insulated and the top portion of the clay had to be trimmed as it was too long and was creating an ice cube effect sitting on the top of the chimney.So, I then followed their advice and had chimneyliner insulated and top portion of clay trimmed by chimney co. Guess what? I still have condensation coming out of the cleanout. I am fed up, have spent a ton of money, and don't trust any of the contractors i have used. any advice to correct the problem would be greatly appreciated.

FYI: Chimney height is 22', it is definitely condensation (not a leak) as we have had very little precip this winter. Sometimes I see white steam coming from chimney cap when boiler is running.

Thanks- Tom


  • Jamie HallJamie Hall Member Posts: 6,653
    I'm sure

    one of the mod-con gurus will chime in on this.  However...

    This is supposed to be a condensing boiler.  In theory, that would mean that your flue gas should be dropping below the condensation point -- in the boiler.  Which is where you would get the higher efficiencies.  If it doesn't, but if it is close, it will condense in the chimney, pretty much no matter what you do to the chimney  It is likely that the white steam is normal condensation when the flue gas is relatively hot and it is relatively cold outside, and the condensation is taking place after the gas exits the chimney; I'd guess that this is happening when the boiler is running harder?

    The gurus will have advice on what to look at.  I must admit that the efficiency you quote strikes me as a little low for this type of boiler -- it's worse than the steam systems I'm used to, which don't even claim to condense -- which may be a tip-off.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ZmanZman Member Posts: 3,476
    Combustion analysis?

    The GA 124 is not a mod con and should not be condensing, Is the boiler piped in a way that will prevent water less than 140 degrees from returning to the boiler? What is the operating temp set to? Is it running at that temp? Does the boiler shortcycle when it runs? How long is the average cycle?

    Has a combustion analysis been done? Look for a small hole drilled in the flue.

    Is it possible the boiler leaks? There could be a pinhole in the combustion chamber forcing steam into the flue. If you turn off the fill water does the system eventually lose pressure?

    I would check these things in this order.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • VictoriaEnergyVictoriaEnergy Member Posts: 126
    edited February 2012
    Condensate in the vent

    The condensate coming out of the chimney could be an indication of an incorrect vent lining system being installed that won't last.  Might be.  Defiantly warrants a close look.

    Have a look at the venting section of the installation instructions provided with the boiler.  I think this is a unit that typically requires a smaller (3" or 4") vent made of a high tech stainless alloy.  the Joints in the pipe lengths should have gaskets in them making the vent system water tight.  Usually near the boiler there is a tee with a condensate drain built in to it.

    Like this stuff:

    If the chimney is an exterior one, insulation becomes important to avoid the possibility of the exhaust icing up and choking off the vent in extreme cold weather.

    Its very doubtful you have leaks.  Newer higher efficiency equipment generally have exhaust that is completely saturated with water vapor.   This is due to very low excess air in the burner design and the absence of a draft hood or draft regulator that allowed additional air to enter the vent.  That additional excess air and dilution air has a benefit helping dry the vent out, but it did so at the expense of overall efficiency. So your new boiler should have a vent system designed for continuous condensation without harm.

    Please post your outcome.
    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
  • TOM1124TOM1124 Member Posts: 5

    I'm sorry I'm not a plumbing professional by any means so the wording is somewhat foreign to me. By the vent you mean the pipe that drafts the boiler into the chimney? If so then have a 6 inch vent. Then the ss liner is 6 inches also. You think I should have a smaller vent pipe then?

    Ps i have a buderus logano 124x gas boiler (non-condensing)

    I looked at the install instr and specs..seem to be very general and not specific regarding my issue.
  • JeffGuyJeffGuy Member Posts: 70
    edited February 2012
    Condensate expected

    According to the Installation and Maintenance manual for the GA124, you should have had a condensate trap installed as part of your boiler installation. See page 28 with the big note: "USER NOTE - A condensation trap must always be installed at the flue vent.". So that must be fixed unless what you are calling the "chimney cleanout" is actually this trap.

    It sounds like your venting may also not be correct. But if it was wrong and a guy from Buderus came out to look at your system, surely he would have said that. Compare it the to drawings on page 28-29 or post good pictures here.

    Where is your combustion air coming from?
  • kcoppkcopp Member Posts: 2,746
    jeff, wrong boiler

    its a G124... atmospheric. Not a GA124 that is power vented.

    Is this chimney an outside chimney?
  • TOM1124TOM1124 Member Posts: 5

    Yeah its an outside chimney.

    And you are right he had the wrong boiler. Its not the GA boiler. Its the Logano G124. I looked up what im supposed to have and its correct with the 6 inch.

    Pictures hope these help..
  • kcoppkcopp Member Posts: 2,746
    edited February 2012
    That looks like a .....

    tough one. The chimney is cooling the flue exhaust off too fast and it condenses.  Can you insulate that chimney on the outside at all? So is the liner just insulated up top? How big is the opening that the liner went down? A insulated liner or B-vent would be best.
  • TOM1124TOM1124 Member Posts: 5

    the opening the liner went down is approx 7.5 inches. i think its a chimney issue, not a boiler issue. however the chimney guys all seem like crooks. I called a few and when I tell them my issue they really dont have an answer for me. Usually the answer is once the liner is installed, the condensation should stop. Unfortunately for me it hasn't. 

     Anyone live on Long Island who can help me or recommend someone id greatly appreciate it. As you can see its not just water, its corrosive water eating away at my walls. Need to fix it asap.
  • Mark EathertonMark Eatherton Member Posts: 5,582
    Sweaty Betty....

    I've run into this on numerous occasions.

    There is a fixed draft relief hood on the back of the boiler where the vent connector connects to the appliance. It is allowing a significant amount of dilution air to flow into this relief hood, thereby lowering the flue gas temperatures to the point that they condense. The ONLY solution I have been able to find is to install a barometric damper on the flue pipe, and block off the factory relief hood. When properly adjusted to -.02" W.C. draft at the breaching, it will only draw what is necessary to maintain a good stack action, and avoid cooling off the flue gas, and associated condensation. Whoever installs the barometric damper should also install a roll out detection/protection switch at the barometric dampers relief air inlet. Your boiler already has one, it just needs to be relocated when the barometric damper is installed.

    Good luck.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Paul48Paul48 Member Posts: 4,229

    repipe it primary/secondary,or use setpoint or delta-t circulators.
  • Robert O'BrienRobert O'Brien Member Posts: 2,930

    If that chimney is lined,why is the condensate coming out of the cleanout? BTW,I'm in Port Jefferson.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Paul48Paul48 Member Posts: 4,229

    What does Buderus say about it? Controlling return line temps won't help?
  • Mark EathertonMark Eatherton Member Posts: 5,582
    Didn't help at all Paul...

    We threw anti condensing valves (ESBE) on the returns of the boilers before we modified the vent, and it had no affect at all.

    The factory, quite honestly, had no idea what was causing them, nor what to do. All combustion parameters were spot on.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Paul48Paul48 Member Posts: 4,229

    the good folks at Buderus read the wall..... They should,it is an invaluable tool for them. You came up with what would be a simple engineering fix for them.
  • JackJack Member Posts: 936
    A bit of background

    Yes, the chimney liner had to be installed. I "think" the 6" is to large, but do not have a manual to confirm that "kinda/sorta qualified opinion". Anyone with the venting tables who can help me out with sizing. On the Island a very qualified chimney man is John Pilger of Chief Chimney Sweeps. He is a member of the NFPA 31 committee, a certified chimney sweep and a good man. Google is your friend. IF the books allow 4" I'd reline with B vent. 4" will fit in your 6"liner, assuming it is a straight shot. Google Dura-Vent and look over the B vent section to familiarize yourself with this product. As well, regardless of what size the books support, you should get rid of the single wall vent connector from the boiler to the chimney. Replace with the proper sized B Vent. That probably is not 6".

    Years ago Rich Krajewski of Brookhaven Labs did a thorough venting study and what he said was that no matter what type chimney, flue height, diameter, etc, the thing that consistently made the most difference in overall system performance was installing an insulated vent connector.

    Every appliance, in the right conditions will condense. The goal is to minimize the "wet time". This requires a low mass liner that will not sit and absorb heat, further reducing the stack temp, which will lead to condensate or longer wet time. One question I would ask is how are the run times? Is the boiler oversized. If that unit is short-cycling with an external chimney you may not have as big a flue problem as you think. Short run times will not allow the flue to heat up, dry off and draw properly and relatively dryly. That would not be good news for all involved, but....? Keep us posted as to your findings.
  • IronmanIronman Member Posts: 3,406
    Jack, I Agree

    That short cycling may indeed be the cause.


    can you give us a little more info? How many square feet is your house? What size is the boiler (btu input or full model#)? What type of emitters do you have? Cast iron rads? Fin-tube baseboard? Can you clock some run times and average them? Don't do it after just turning up any thermostats, that will skew it.

    I would also give serious thought to what Mark said. It might be a combination of that and short cycling.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • Paul48Paul48 Member Posts: 4,229

    boiler is cast iron and should have by-pass piping. At 85% efficiency you're pushing it with the condensing point anyway.
  • TOM1124TOM1124 Member Posts: 5

    Input Rating is 133 Btu/h, Output is 109 Btu/h. Model # is G124x/32/5 II.

    My house is 1300 sq ft cape cod style. 4 zone heating system. (upstairs, main, basement, hot water tank). Slantfin Baseboard throughout the home.
  • IronmanIronman Member Posts: 3,406
    Waaaaay Over-sized

    Your boiler output is 109k; you have a 1,300 sq. ft. house: that comes to almost 84 btu's per sq. ft. You need to do a heat loss calculation, but even a leaky, poorly insulated house on L.I. shouldn't need more than about 40 btu's per sq. ft. - and that's when it's 0* outside. At 35*, the load would be half. Add to that the fact that you have four zones and only one may be calling, and you'll certainly have short cycling.

    Any time a boiler starts cold, there is going to be some condensation produced. Just like the tail pipe on your car when it's cold. However, the boiler should run long enough to burn off the condensation so there is no damage to the venting or boiler. When it's over-sized like yours is, it doesn't run long enough to burn off the water which is acidic and then the problems start.

    The simplest solution is to install a properly sized buffer tank that would ensure a minimum 10 min. run time when only the smallest zone is calling.

    Tell us how many lineal feet of baseboard is on the smallest zone and we'll be able to size the buffer tank. Measure the length of the elements inside, not the length of the enclosures themselves.

    Installing a buffer tank will also provide a means of hydraulic separation between the boiler and the system in lieu of pri/sec piping. This will help ensure proper flow rate through the boiler and maintain a proper Delta T, which is all good for extending boiler life.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • HenryHenry Member Posts: 698
    Too big a chimney on an outside wall

    I got one this week. We installed a Raypack residential 180,000 BTU over two years ago, BTW P/S! Customer got 25 to 30% savings. There was an insulated exterior chimney. A wind storm knocked it off. It was replaced in late summer. We have had several calls of no heat and the CO detectors going. The chimney was back-spilling and ice was forming on the cap. We had the chimney guy remove the bird screen. We had another back spilling into the boiler. As per the AHJ, there is a combustion air inlet 12 inches from the boiler and the ground.

    So, Monday I go to the site to do my detective work. According to code, the boiler required 6 inch vent. According to Security Chimney, a thimble and heat guard was required when the chimney came within 2 inches of combustibles. They cut a 1/2 larger hole in the floor of the balcony to pass the chimney. I checked with Security Chimney and they also said 6 inches. We had removed the cap on the bottom TEE to find it full of condensate. The actual vent diameter was 8 inches with 1 inch insulation. The previous exterior chimney was 6 inch vent with two inches of insulation. TOO big a chimney, problem solved.

    In your case, I used the Z-Flex slide rule to find that in you situation the actual vent size required is 5 inches! I also feel that your liner, if it is there, is not properly installed. There should be no condensate coming through the door!

    An oversized chimney with an improper installation and a short cylcing boiler is only going to give trouble

    Here is a supposed pro liner installation by a chimney only contractor. It was only partly done!
  • VictoriaEnergyVictoriaEnergy Member Posts: 126
    edited February 2012
    It'll still condense

    I still think the best option will be switching to a stainless vent system designed for continuous condensing.  You have a non-condensing boiler, but you definitely have a condensing vent system.  Even if the boiler gets set up for longer run times, the vent damper is going to shut off the chimney when it's not running and it will cool right off again.  There so little heat going into the chimney for its size and being exposed.  Eliminating or clipping off part of the vent damper would help by keeping the vent flowing and warm, but a significant efficiency loss will be incurred ( you did buy the  thing to reduce heating costs,.. right?).  

    Since it does have a draft hood, the vent has to be bigger, at least a 5", and maybe back to 6" (according to Can. Code) if they have to use a corrugated flex liner (used if the flue isn't straight).

    Using B vent for vent connector might help, but I don't recommend it since there is always corrosion potential between the stainless liner and the aluminum inner jacket of the B vent.

    I also hear you are frustrated by this issue and want it solved.  I don't think anyone here would say that any of the other alternatives would work with 100% certainty.

    One other alternative would be installing a Teerlund power venter and convert the boiler to side wall venting.  The down side is the cloud of steam/exhaust that you will then have coming from the area of the terminal.  This would cost a lot less.
    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
  • Chris SChris S Member Posts: 177
    Condensation problem


    I had a similar problem with one of my installs, also NY a little N of you, but I don't think the proximity to the water is relevant. In my case- exterior chimney, 5" liner- the chimney sweep who is a long time friend recommended an insulated liner, but it would not physically fit inside the clay. I fought with this for several months, a condensate drain was an option, but I did not have anywhere to run the drain to.

    My install was primary secondary with 6 zone valves, and a properly sized boiler- but with one or 2 zones running it would short cycle & condense. I changed out the gas valve to a 2 stage gas valve ( the boiler was rated for this, and parts were available from the manufacturer). In hindsight I installed the wrong boiler. This change allowed longer cycle times, and the condensation problem was solved immediately.

    As suggested- a buffer tank would work in your case, or perhaps an external control like a HW+ . I have found these to be very helpful in reducing short cycling, this may be the least expensive way to try & resolve this.
  • Mark EathertonMark Eatherton Member Posts: 5,582
    They read the Wall...

    But it doesn't seem like they respond. Quite honestly, theirs is not the only problematic appliance, but the more the base efficiency, the faster the problems show themselves.

    ALL manufacturers of atmospheric appliances would benefit from a barometric damper, and their engineering departments know this, but the marketing and sales department are running the show and driving the bus, and if it increases the cost one dollar, than its chances for survival are slim to none because no safety benefit is seen or perceived.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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