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Condensation Issues in Chimney with New Boiler

dziukapdziukap Posts: 5Member
We just purchased a new home in CT. It had the original 1960 Arcoleader oil boiler in it that was eating 35 gallons of oil a month just for domestic hot water. We replaced it with a Buderus G115WS4 linked to a stainless steel crown indirect. Great system by the way, sips oil.

Our installer, who was great and very knowledgeable(licensed Buderus installer), warned us that with a 2 story brick chimney on top of the story of flue in the foundation wall, we would get condensation issues, and probably have to line the chimney with stainless steel, but he said wait and see what happens. Well lo and behold, the boiler finally ran hard all night for the first time this week and we have about a quart or so of water dumping out of the lower flue door every night now from condensation(it's not running back to the boiler, we have a flue access clean-out built into the 10 inch poured concrete foundation).

Our installer is on vacation until December 2nd, so until I can discuss it with him I'm interested in getting as much info as I can.

First of all, our chimney has a combined flue for our living room fireplace and the boiler. If we line it with a reduced size stainless steel flue to reduce condensation and eliminate condensation damage to the mortar, that pretty much means our fire place is DOA correct, or will they be able to set it up so we can still use the fire place? It's just a standard fire place, not a wood burning stove.

Secondly, the installer said that the Buderus' flue exhaust temperature is so low due to it's efficiency, that even with proper sizing and lining, you can't eliminate condensation completely with a 2 story chimney because there is so much cooling off that happens by the time it exits 3 stories above, and it never runs long enough to really heat the chimney up and burn off the condensation. In that case, what do people do to control the moisture? I don't fancy having a water logged towel by our flue every night for the rest of our lives, even if it isn't damaging the chimney anymore. I believe the G115WS4 can be switched to a direct vent set up without a power vent(maybe I'm wrong?), but it would be VERY difficult to meet code with the orientation of our house, and exterior items where the venting would need to be, and costly to modify the chimney this way.

Well, we knew this was probably coming, now it is just a question of making a decision.


  • icesailoricesailor Posts: 7,265Member
    Is this a three sided outside chimney that goes all the way up the outside?
  • dziukapdziukap Posts: 5Member
    edited November 2014
    Yes, the foundation is 10" thick, then there is a concrete bump-out cube in the ground that extends outside the foundation that the chimney sits on. 3 sides of the chimney are external walls. The fireplace flue starts separate and then joins the furnace flue at a 45 degree angle at about 8 feet off the ground outside. The chimney then extends up both stories and about 3-4ish feet above the roof line.

    The home is a 2-story colonial, and the gable end with the chimney has 4 windows on it, 2 windows on each level, one on either side of the chimney. It is my understanding that we could have just put a hole in the chimney with a vent pipe and cap sticking out, except of course now you are venting exhaust below your 2nd story windows which is both dangerous and illegal.
  • SpenceSpence Posts: 316Member
    There is no such thing as a vent heating up and burning off condensation. If flue gasses move up a chimney too slowly, they will condense. Also the opposite is true; they condense if moving too quickly. The correct "speed" depends upon your connector sizing and rise, and the height and size of your common vent (chimney). The code takes these issues quite seriously, giving clear instructions on how to calculate the proper vent system. These instructions are the former GAMA Tables and could be found in your boiler IOM.

    It doesn't seem possible that your fireplace and your boiler are in the same common vent; that is a clear code violation. There should be a wall inside your chimney that creates distinct passages; one for your FP and the other for your boiler and DWH.
  • Jamie HallJamie Hall Posts: 8,232Member
    First, as Spence says, if your fireplace and boiler are venting into the same flue -- even if it is some distance above the fireplace -- it is a serious code violation and very dangerous, to boot. You might be safe enough using the fireplace -- but I wouldn't use the boiler until you verify the situation; if something (a dead raccoon?) blocks that single flue above the fireplace, the boiler would vent into the living area and that's not good.

    Now... having said that. Yes, you may get condensation in a chimney, particularly an outside one, and in your situation a liner is probably a decent idea. If it is a shared flue, that would knock out the fireplace, as you note, so the alternative is a new separate flue, built according to code, lined and sized for the boiler, alongside the existing one.

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

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Bob BonaBob Bona Posts: 2,081Member
    The boiler and the fireplace should have seperate flues. A SS liner is the next move. Would not power vent even if clearances permit-noise, siding staining, weak link issues.

    Most important: the WS4 has adjustable/removable baffles to dial in the stack temp for your site. Ask your installer to eval.
  • icesailoricesailor Posts: 7,265Member
    Lets assume that the boiler flue and the fireplace have different flues. Because they surely do have separate flues.

    The bigger issue and cause of the flue condensation is the 3 sided outside chimney. That sounds like a minimum of a thirty footer. You can't heat it.

    From one of my last Massachusetts CEU's for plumbing & gas, as far as I understand, you can not vent a new gas appliance in to a three sided (outside) chimney. Even with a liner. The Massachusetts gas codes "Exceptions" don't allow it. We never had CEU's for oil.

    Your flue probably doesn't work for squat anyway. Put in a Power venter and be done with it. They work well. You'll get used to the noise. I always preferred Tjernlund over Field. Some prefer Field SWG's. Both work. If it was in Massachusetts, and it was a gas replacement, you'd be switching vents because it would be illegal to vent into a 3 sided outside chimney.

  • Bob BonaBob Bona Posts: 2,081Member
    Ice, the WS4 is oil. Oil power vent of any kind when there is a functional chimney is ludricrous and a service call waiting to happen. Op said there isn't clearance or desire for one anyway.

    "You'll get used to the noise". Seriously?
  • SpenceSpence Posts: 316Member
    You can indeed get used to the noise, provided you live next to the airport.
  • icesailoricesailor Posts: 7,265Member
    I said that in Massachusetts, with gas replacements, you need an inspection. It must be lined, and it can NOT be a 3 sided chimney. Because of condensation. I also said that I was unaware of what the regulations are on oil. Ask Firedragon. He is the recognized expert on the oil subject.

    As far as getting used to the noise, if you have a choice between being cold and no vent, because of a 3 sided chimney, and listening to a Power venter, you'll learn to get used to it. Like I have had to with hi high tech new high SEER air handler in my new AC system. Louder than any Power venter I have ever heard. When it runs, you have to turn up the TV volume.
  • Bob BonaBob Bona Posts: 2,081Member
    I don't need to ask George anything at this time, thanks.

    Something is misapplied/installed wrong if you have the howl of a PV in your central ac. 20 SEER or 13 SEER. Throw it up here on the Wall and maybe we can figure it out.
  • SpenceSpence Posts: 316Member
    It's one of three things; (1) the ductwork; (2) the ductwork, or; (3) the ductwork.
  • icesailoricesailor Posts: 7,265Member
    More like the Design, the design and the design of the Air handler and the housing. There are some "issues" with the install, but some of us know that when the real experts that get paid the big bucks, who tell us we don't know what we are talking about get done. there are consequences.

    Example: If you have a high airflow through an open door, it will be quiet. As you close the door, the air makes more noise. Until the door is closed. The air rushing past thingy. If you have a AH case, now made of super insulated and soundproof plastic and insulation, and have the same size fan cage but a smaller space for the air to enter the inside, someone in the design phase screwed the pooch. It all gets back to that efficiency thingy. Just because something is more "efficient", doesn't mean it will cost you less to run.

    Unless designed by Germans.

    I bought a new BMW (almost new, a Corporate car with 11,000 Executive miles) 2014 X1 128XI. My old one had 153,000 miles and ran like a clock. Still got 28 MPG on the highway at 70 to 75 MPH. But 16.5 in traffic being careful. 2.5 Liter gas engine. The new one has the standard 2.0 Liter turbocharged 1240 Hp motor, It gets an honest 24 MPG and higher. Highway, I don't know yet. I bring this up because it has all these gas sipping features. One being that it shuts the engine off when you stop at a light. As soon as you take your foot off the brake, it instantly starts. I can watch the computerized fuel monitor going up. The old car, at the long lights I experience, I watch it go down.

    Why are some so obsessed when they hear their burners start? To the point of obsession? When the Germans have devised a way to save fuel, have a well running and efficient vehicle, that stops and turns itself at every opportunity? You can shut it off, but why would you?
  • dziukapdziukap Posts: 5Member
    edited November 2014
    Okay so, I've never had a fireplace before, so I was guessing that the flue was shared based on the outside appearance of the chimney, I haven't been up to the top yet to check. If it is that dangerous I'd assume they are separate, as I had 3 companies look at the house and give me quotes before the install and nobody mentioned it.

    All three companies also said the same thing about the condensation: the chimney is currently lined with tile so wait and see what happens. I'm assuming then that they all felt the size of the current flue was at least close to what it should be.

    When the installed the boiler they tested for back drafting and evaluated the size of the air space the boiler is drawing from and passed it. Could it be that somehow it can't draw enough air or is the issue most certainly with the flue? I don't want to pay to line the chimney if it could be solved by simply bringing in an outside air supply.

    As you can tell I am no expert, I am searching here more for the questions I should be asking. I realize you all can't solve this over the internet.
  • GordyGordy Posts: 7,937Member
    You have two seperate flues don't panic. One chase with two flies inside separated by a wyer. Basically a brick wall between the two flues.
  • GordyGordy Posts: 7,937Member
    edited November 2014
    Glad I don't live in mass. Ice there are three sided chimneys up the kazoo in the Midwest. Just about all chimneys are 4 sided when they bust through the roof line. So illegal???
  • SpenceSpence Posts: 316Member
    There should never be a wait and see with a vent system! Look at the previous post. If sized properly according to the code and Buderus, there is no "maybe." The vent system will do it's job the right way without worry. If you need a copy of the vent tables I can help.
  • icesailoricesailor Posts: 7,265Member
    Gordy said:

    Glad I don't live in mass. Ice there are three sided chimneys up the kazoo in the Midwest. Just about all chimneys are 4 sided when they bust through the roof line. So illegal???

    Its not the coming through the roof with 4 sides, they are limited to how high you go above the ridge line to get to a legal height. Its the ones that run up the outside that are the problem. With a standard Cape, you can easily have over 30' of 3 sided chimney and then the 4 sided part above the roof rake boards.

    As soon as I read that he had condensation from the new boiler, I knew it was probably a 3 sided chimney. Haven't you ever seen chimney vents covered with rust inside with rust stains running down the wall? Bet it will be a 3 sided chimney. You might find it is a national gas thing now. Tim Mc would know. If it isn't, it will be soon. But we're talking OIL. In Massachusetts, oil is inspected by the Fire Departments. Who often are clueless about the oil burner codes. Some barely know what an oil burner or boiler actually is. I didn't or don't make the rules. I just had to follow them. The question was about condensation out of a chimney flue. A bigger problem with long 3 sided chimneys is in tight houses, when the burner is running, the fireplace flue becomes a fresh air vent. If the wind blows across from the boiler flue and then over the fireplace flue, it can recycle the flue gasses from the boiler in to the house.

  • GordyGordy Posts: 7,937Member
    I don't disagree that three sided chimneys are not the greatest ice.

    It's just people are stuck with them. Lots have worked for
    A very very long time, but it takes high stack temps. Now days everything is more efficient so those high stack temps are not the case anymore.
  • SWEISWEI Posts: 7,356Member
    Surely there is a recipe for making a 3-sided chimney work well. I'd be interested to see how a stainless liner foamed in place using something like AirKrete would perform...
  • RobGRobG Posts: 1,850Member
    Why not just a stainless liner and perlite?
  • SWEISWEI Posts: 7,356Member
    I never claimed to be a chimney guy, just a curious engineer. Would it allow a 3-sided chimney to perform adequately?
  • GordyGordy Posts: 7,937Member
    Basically what it comes to is how often that boiler fires through out the day with conventional equipment. The more firings, and longer length of heating cycle the warmer the flue stays. With tightening the envelope there comes unintentional consequences. The less often that same boiler fires, and shorter heating cycles the More the flue cools between firings. Thats when it becomes important to insulate that flue to help keep its temp up.

    There is a way Kurt. Just not everyone understands what happens with the mechanics of it all. Sometimes things change indirectly related to the flue with out realizing its effect to the flue.

    Going from a boiler that was grossly oversized to just right has an effect.

    I have a three sided chimney that has a fireplace, and seperate flue for boiler. It's not lined no problems for 62 years of service. There is maintenance to any masonary chimney.

  • SWEISWEI Posts: 7,356Member
    Makes perfect sense the way you explain it.

    Yet another benefit of proper equipment sizing!
  • icesailoricesailor Posts: 7,265Member
    I haven't yet seen any insulation make something warm of cold. Just act as a barrier to the transfer of heat or cold.

    Among the oil teaching experts like Firedragon, it was advocated that 400 degrees was the best temperature for the best overall combustion efficiency. I personally say that down firing a oil boiler below 350 degrees might give you spectacular numbers, but the boiler/burner ran like crap. Because you needed that hot flame for complete combustion. If its 70 degrees out, a three sided 30' chimney won't get a lot of cooling. Let it be 10 degrees out and the story is different.

    WIth clean combustion in automobiles, they get clean combustion by getting the motor up to operating temperature as quickly as possible. That's why they use Exhaust Gas Recycling to get the intake air hot and cut out condensation. Which ruins exhaust systems. That have a long warranty. They will last as long as the warranty. Get a Midas replacement and it rots out in 2 years. Will one of the first rumblings about CNG cars have to do with all that condensation eating up the exhaust?
  • GordyGordy Posts: 7,937Member
    I think it's fair to the OP to explain what exactly happens that leads to the need to change a flue configuration.

    These are changes not only to the heating plant, but to the rest of the structure over the course of years since its conception.

    Usually with older envelopes change happens in small increments as thought needed, or as can be afforded to accomplish.

    All the evolving envelope upgrades create huge impacts in the end result. Ending with a replacement heating plant of better efficiency that can no longer use the same flue configuration for venting that's worked for decades because it's exhaust temp is no longer hot enough to keep the flue from being damaged by excessive condensation.
  • GordyGordy Posts: 7,937Member
    The bottom line to the OP is if your getting condensate on the floor from the flue it's time to line the flue, and insulate it.

    Lining does not stop condensate alone but it protects the masonary from damage due to corrosive condensate. Insulating will allow that liner to warm up quicker, and stay warm longer.
  • icesailoricesailor Posts: 7,265Member
    edited November 2014
    If the flue has a tile in it, and it was inspected and passed, it is considered OK.

    The issue is that if the replacement had been a Weil-McLain WGO boiler that is running at 400 degree compensated stack temperature, there would be no where the described amount of condensation.

    But we have a Buderus, running at 300 degrees (compensated?).

    Does that compute to 25% less available stack/exhaust heat to go up the chimney? What is the tile size? If it is a 8"X12" tile, it is too big. The boiler can't heat a tile flue that size. It should be a 8" X 8". When you install a SS liner, you are choking down the size of the flue. And Stainless Steel is a terrible source of heat transfer. Remember when Arco's had stainless steel combustion chambers? That burned out?

    There's more to chimney flue sizing that standing back holding a pencil at arms length.
  • dziukapdziukap Posts: 5Member
    edited November 2014
    Okay so the stack temperature has been adjusted up, with a guestimated loss of about 3%-ish efficiency. IF this solves it I'd be tempted to just leave it, as the cost to line the chimney would take a LONG time to gain back by getting that efficiency back. However there is the side of me that always wants to do things the "right" way.......

    I can easily afford to line it but I don't want to spend money just for the hell of it. We may not be in this house the 10+ years it would take to see the break even point. However, if we sold the house someone may want it done anyway then I still get to pay for it but we didn't get any savings while we were in it.......

  • JackJack Posts: 1,021Member
    This is the way the oil business is run. Three good companies all indicated that the outside chimney was likely going to be problem. As they acknowledged it they are off the hook for it. Check Appendix E in the NFPA 31 book. E has been kept an appendix for 20 years specifically to avoid companies having to reline flues. The cost of the SS liner is thought to be to high (correctly) and would limit the number of oil systems, also correct. The sizings in E have been reliable. In a pinch I've been involved with systems that used 4" pellet vent (L-vent) successfully as a liner. You need the support of the equipment manuf, contractor and ahj for that to happen but if the system/chimney configuration is right the 4" worked. YMMV of course based upon the firing rate, vent connector type, chimney height etc.

    The unfortunate part here is that when the chimneys likely problems were brought to your attention PRIOR to the sale that a discussion of what would be necessary should the vent condense. The discussion would have been, "this may happen so here are some reputable chimney sweeps in the area…" You then evaluate from that point on a total cost basis. You own a heating SYSTEM. It is a system from the oil fill cap to the boiler, heat emitters, and chimney top and must always be evaluated and treated as such.

    That is an excellent boiler, btw!
  • icesailoricesailor Posts: 7,265Member
    dziukap said:

    Okay so the stack temperature has been adjusted up, with a guestimated loss of about 3%-ish efficiency. IF this solves it I'd be tempted to just leave it, as the cost to line the chimney would take a LONG time to gain back by getting that efficiency back. However there is the side of me that always wants to do things the "right" way.......

    I can easily afford to line it but I don't want to spend money just for the hell of it. We may not be in this house the 10+ years it would take to see the break even point. However, if we sold the house someone may want it done anyway then I still get to pay for it but we didn't get any savings while we were in it.......

    Or a new buyer might hire a home inspector or a bank requires one. They see that the chimney isn't lined, and the buyer wants it lined or they back out. Or they hold back $20,000 from the sale, the cost to be deducted from the $20,000.

    And THAT my friend happens all the time.

    In this day and age, they run the building permits and anything that is outstanding, no matter how far old, will hold up a sale until it is resolved. Have a addition done without any permits, and the world ends. Local reg. about oil tanks? Some tree hugger gets the Board of Health to pass a local reg. allowing ONLY double wall tanks. Even though the tank is 8 years old, in a cellar with a concrete floor, it has to be removed. Buyer comes along. Going to change to Nat Gas. No matter. You have to remove the oil tank before the sale goes through and replace it with an appropriate tank. Even though it is going to be torn out and not put back.

    You have no idea about the level that chicken feces has dropped to.

  • dziukapdziukap Posts: 5Member
    Well, the raised stack temp helped a lot but there is still a fair amount of condensation. In goes the liner ASAP. I'll keep you posted.
  • NYCDaveNYCDave Posts: 65Member
    looking at an oil-to-gas conversion, and have a three-story three-wall chimney, so worried about condensation... did your liner solve the issue? We won't have a condensing unit, just a standard mid efficiency gas-fired boiler, but still concerned...
  • binkbink Posts: 81Member
    edited August 2017

    Did not notice this an older post. I assume problem was resolved by op.
  • newagedawnnewagedawn Posts: 545Member
    its not a 3 sided chimney,it only looks three sided from the outside, lol, homeowners, and i bet that the appliance and fireplace have separate flues, i live in CT and have only seen a few combined flues in all my days here, it happens but not to common and they are older homes that where homeowner built,(again lol, homeowners) fireplace and appliance flues SHOULD ALWAYS BE SEPERATE !!!!

    that being said,
    here in the north east you should always line a Buderus boiler with the required flue size, Buderus will even tell you the chimney flue must be 8 by 8 minimum, which helps when lining the chimney with the called for flue which for the G115 is 5"
    Buderus boilers run at a very low flue gas temp usually around 250 to 350 for oil fired(and i'd bet the boiler in question is oil, cause 85% of CT is oil) which is right in flue gas condensation temp range

    that being said
    YES, this boiler does need to be lined and if the flue gas continues after the lining of the chimney with the 5" liner
    then some of the baffles need to be taken out to raise the flue gas temp to 450 minimum, once a 450 minimum temp is reached with an 11% to 13% Co2 and a .05 draft
    your flue gas problem will disappear
    a word to the wise homeowner, LOL
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
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