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Help to determine the correct size & type of chimney liner.

MikeAmann
MikeAmann Member Posts: 422
edited January 20 in Chimneys & Flues
After reading many of his replies, I sure hope Bob Harper is still around......


Up the Chimney
The gas going up the chimney or exhaust pipe includes a large quantity of water vapor. When everything is working properly, the vapor is pushed up out of the end of the pipe and into the atmosphere before it condenses. If something is awry, the vapor cools before it exits the flue and condenses right then and there. In order to stop the vapor from condensing, conditions must be adjusted so that it does not cool before leaving the chimney.

Size Matters
A flue that is too large allows too much air to circulate, making it difficult for the warm gas and vapors exiting the furnace to create a strong updraft up and out of the vent. Instead, cold air from the top pushes the warm air down and traps it in the flue. As the vapor sits in the flue it cools, creating condensation.

Downside of Upgrades
New furnaces hooked up to existing flues can result in condensation problems because they are more efficient than old models. While much of the heat produced by older heaters was lost out the flue, this heat prevented condensation by keeping the chimney or vent pipe warm so that air moved upward. Newer models keep most of the heat moving into the home, which results in a cooler flue. This means that the vapor has a much greater chance of cooling and condensing in the flue than it did with the old furnace.

Danger, Danger
Condensation in the flue or vent pipe is not dangerous in itself, but can create a dangerous condition. Over time, the moisture, as well as the chemicals released by the furnace, can damage the flue and vent pipe. Rust and corrosion create leaks that allow the vapor to make its way into your home. This exhaust from the furnace contains dangerous carbon monoxide. Have a technician check the flue for leaks and test your home's carbon monoxide levels if you notice moisture in the furnace vent. Carbon monoxide is odorless and colorless, and it can be deadly.

Recently I made my oil-fired burner more efficient (84-86% now) by converting to a flame-retention head and reducing the firing rate (currently .71 GPH), and now it is raining inside my chimney flue. It's an exterior chimney (3 sides exposed) and the clay tile flue liner is 6" x 8" and has no bends or offsets. No other appliance shares this flue and the water heater is indirect. The other flue is for the fireplace, which will never be used by me.

I have been doing the research for the last few days and I believe I want (need) a smooth wall heavy gauge 316 stainless liner with an outer wrap of insulation (no TherMix). I definitely do not want a thin-walled corrugated liner!

This boiler has a 1.10 GPH max firing rate and the flue collar is 7" round.
If I were to use only a 1/2" of insulation around the outer diameter of a round pipe, then the maximum diameter of pipe that I could squeeze through the 6" x 10" rectangular clay liner would be 5".
Is that too small for my firing rate?
Is rectangular pipe available to do this?
«1

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 18,920
    This is really a question which needs to be asked of a qualified and licensed chimney sweep -- but off hand, since the effective size of the 5 inch is less than half the flue collar of your boiler, I'd have to say... probably no hope. Too small, and I don't know of any rectangular liners.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 11,988
    @MikeAmann

    I have always understood that a liner the same size as the boiler flue connection is always large enough. Sometimes if the chimney is high enough the size of the liner can be reduced.

    If you go on to a liner MFG web site like Hart & Cooley I think they have calculators. I am sure @Bob Harper is the expert on this.

    I don't believe it is mandatory to insulate a liner do to the fact that they are thin and don't have much mass they heat up almost instantly
  • Bob Harper
    Bob Harper Member Posts: 914
    The codes provide sizing tables based upon empirical calculations- not measured performance. Liners for gas and oil are not required to be insulated. Actually, if you block off the air at the top and base it is air insulated, much like a Dewar's Flash (Thermos Bottle). The code sizing charts are there to "allow" or suggest it's ok to downsize. Otherwise, all you'd need to do is vent into a chimney liner the same size as the appliance collar or larger without the charts.
    There are conflicting opinions as to downsizing liners and if there is such a thing as oversized liners. Your chimney is exposed on 3 sides and thus deemed an "exterior" chimney. Regardless of opinions, it is well documented that warm chimneys can maintain a stable draft long term better than cold ones. When an appliance first fires, the chimney is full of cold dense air. This must be lifted out of the flue by the rising lighter gases. The amount of lifting force is called "draft'. It is the difference in densities of the flue gases relative to the surrounding air, which results in the lighter air rising as the cooler denser air displaces it. The hotter the flue the greater this differential. If the walls of the flue are wet with condensation, the surface of the flue cannot rise above 212F until it has dried. This consumes some early BTUs. Next, the wall of the flue absorbs more BTUs. Here, a high mass liner, such as terra cotta, absorbs more BTUs than a thinwalled corrugated liner. If the terra cotta tile does not have the requisit 1/2- 4" air space but was backfilled with mortar, it will continue to wick heat away from the flue gases thus inhibiting draft. Light liners of aluminum conduct 3x the heat of stainless steel. Thus, aluminum liners and B-vent have weaker draft and can condense worse than ss liners or L vent.
    Where you have a larger liner, the flue gases will tend to vent up the center as gases in contact with the wall of the liner cool and, in effect cling to the wall (static pressure). This means a large flue can vent an underfired appliance but only to a point. As the cold wall of the liner robs heat, draft will begin to suffer. This is where sizing to the appliance comes in. A grossly oversized flue full of cold air can cause flow disturbances as the hot gases try to push past the cooler gases around them.
    In the example given, you are probably underfired, which can result in excessive condensation. Guided by combustion analysis, try increasing the firing rate. Once tuned, provide 3-4 minutes of post-purge and your condensation should go away. You can use a ss tee at the base of the liner, but I prefer a wye fitting whose bottom branch provides a convenient port for inspection and servicing, while providing a sump for condensate.
    you might get by with a 5.5" smoothwalled round liner but to be safe I recommend getting a 6" smoothwalled liner ovalized to about 5"x7". If you're really worried about it, have a chimney pro bust out the terra cotta and install a 7" ovalized liner to fit.
    You do need to keep the connector the same size as the appliance collar. Make the run to the chimney as short as practical. There is a trade-off between shortening the run versus getting some vent rise straight up before any offsets. This allows the flue gases leaving the appliance to develop some velocity before they hit the resistance of an offset or lateral run. NFPA 31 requires the male end-up. I think this is foolish. A male-down allows for condensate to remain inside the pipe while a male up leaks outside the pipe. Note that ALL listed venting is male-down. No seams on horizontal runs between 5-7 O'clock and no screws here. Min. 3 screws per joint equidistantly spaced with one screw locking snaplock pipe seams down. On larger pipe than 6" consider spacing screws about every 6-8" of circumference.
    HTH,
    Bob
    MikeAmannSuperTechVegas
  • MikeAmann
    MikeAmann Member Posts: 422
    edited January 21
    @Bob Harper

    WOW, thank you so much Bob. You answered everything, even the questions that I was coming up with as I read your great answer! :) I know now that I can make this work. I now have much less research to do. It all comes down to what I can get for SS pipe. I know that I saw heavy gauge smooth wall rectangular pipe somewhere. And they also have the converter pieces from rectangular to round. Not having to insulate the outside of the pipe makes this so much easier.



    The only question I have right now is about the tee and cap for inspection, which I do want. Is it OK to extend the bottom branch of the tee down to where my cleanout door is and have the cap there so it is easily removable? And I completely agree with male-down. CODE is dumb regarding male-up.

    My boiler always used a .85 GPH nozzle with the conventional head. I am now at a .71 GPH firing rate with the new flame-retention head. The reason that I want to stay there is because this keeps the CO near 50 ppm and increasing the firing rate makes the CO go up higher than the other members here like to see. I also do not want to short-cycle the burner. Unless the SS flue liner drastically changes the combustion analysis numbers, I am happy at the firing rate I have right now.

    You suggested - provide 3-4 minutes of post-purge and your condensation should go away, which I can easily do with my new Hydrostat 3250-plus, but I can actually watch it rain inside the flue (from the cleanout door) while the burner is running when the outside temperature gets below 32 F.


    Look in the tray. See the raindrops?

    I am very interested in sizing the flue to the appliance and my .71 GPH firing rate.
    Can you tell me what the sizing charts recommend?
  • Bob Harper
    Bob Harper Member Posts: 914
    edited January 21
    Round is best followed by oval. Once you get over a 2:1 aspect/ ration you're hindering performance and the extra cross-sectional area doesn't count. Same for the cold corners of a rectangular duct. It's the oval or round that fits inside that really counts. Rectilinear liners are problematic because the unnecessary surface area adds friction to the flow. Be careful of who you buy liners from online is all I can say and make sure of the warranty. A professional liner carries a transferrable, never expiring warranty. Next would be "lifetime", which means to the original owner. A fixed service life is a joke.
    Your baro. damper is close to the ell. You want a min. 1.5-2 duct diameters from any ell or appliance collar.
    If your O2 stays low and your CO is STEADY below 100 but preferably 50 ppm then I'd feel pretty good. Can you provide full combustion analysis numbers including draft?
    Yes, you can extend the liner down to a lower cleanout if the breeching provides reasonable access for inspection and service. I've done it many times on oil and wood. However, with a CMU block wall I'd bust out room for a wye breeching of ss.
    The "sizing" charts in the Annex of NFPA 31 are merely empirical calculations based on a bunch of assumptions and are a joke. If you can't get a big enough liner to a particular boiler, you have to drop the size until it can vent properly or power vent it. Where common vented with other boilers or water heaters you may have to install a priority control or convert the DHW to an indirect tank to reduce the venting load.
    I'd be curious why your CO is so high when firing at 0.85 GPH. Do you have a bypass piped in? If not, look into it.
    Also, what's your ambient Rh%? Humid CAZ can exacerbate condensation. Also, consider how much dilution air is being entrained into the baro. damper. Setting it more sensitive will drive down the draft but introduce more 'dry' air and possibly reduce sweating. You really only need about -0.01 to -0.02 wci in most equipment.
    Last resort would be to pressure test the boiler to ensure it's not leaking into the combustion chamber. Note that things may leak when hot but not cold and vice versa but it's a start.
    If the chimney is missing mortar allowing ambient air into the interstitial space around the flue liners that can cause excessive condensation, too.
    HTH !
  • MikeAmann
    MikeAmann Member Posts: 422
    edited January 21
    @Bob Harper

    Round is best followed by oval. Once you get over a 2:1 aspect/ ration you're hindering performance and the extra cross-sectional area doesn't count. Same for the cold corners of a rectangular duct. It's the oval or round that fits inside that really counts. Rectilinear liners are problematic because the unnecessary surface area adds friction to the flow.
    I understand and agree with this. It's physics.
    Now, I am the type of person that hopes for the best, but plans for the worst.
    So let's say that testing actually confirmed that a 5" round SS liner works best for my boiler. The combustion analysis numbers are great, the burner runs with no smoke, and I have no condensation. But one day, some "inspector" happens to be looking at my heating system and decides to red-tag me because my breach is 7" and my flue liner is only 5" - because the book says.......... (you can't do that).
    This is why I would install the larger rectangular liner - to keep the idiots happy that really don't understand HOW this works and just quote sections of CODE.

    Your baro. damper is close to the ell. You want a min. 1.5-2 duct diameters from any ell or appliance collar.
    I can only move the damper about 4" closer to the wall. I will do that when I add the new liner.
    I was going to do this:

    Would it be better to have the baro damper right at the breach?

    If your O2 stays low and your CO is STEADY below 100 but preferably 50 ppm then I'd feel pretty good. Can you provide full combustion analysis numbers including draft?
    The nozzle this time is a Delavan .70x80B Solid at 120 psi = .77 GPH firing rate.
    IMO, the solid nozzle fills the "bucket" portion of the combustion chamber more completely and evenly, and to my non-professional eye, it simply looks right (very stable) - better than the hollow where the ends of the flame were climbing up into the funnel section of the combustion chamber.

    I measured the draft first. Same as previous -.020 over the fire and -.025 in the breach. I cannot get this any better. Remember, this boiler was designed with large passages needed to move a lot of air. I now require only about 25% of the air that the conventional burner needed - probably even less than that.

    Next I found the TRACE of smoke setting - air band open to 1.750". The first column below is those results. The second column is with 1/2% less CO2 at the same flue temperature. The last column is just a little hotter.


    The previous round of tests was with a smaller (.65) hollow nozzle giving a .71 GPH firing rate.
    The numbers are essentially unchanged. From previous:

    O2 % same
    CO2 % same
    Efc same
    X air % same
    TF f very close, a little hotter due to the increased firing rate?
    CO ppm slightly higher, again, due to the increased firing rate?

    I am happy with these numbers. I think I have taken this as far as I am able to.
    Okay, let's hear from the professionals.........

    Bob, these numbers were obtained when the heat reclaimer was still in place. It is now replaced with a straight pipe.


    I'd be curious why your CO is so high when firing at 0.85 GPH. Do you have a bypass piped in? If not, look into it.
    Bypass? Please elaborate.

    Also, what's your ambient Rh%? Humid CAN can exacerbate condensation.
    There is a dehumidifier at the other end of the basement with digital readout. Humidity is 60%.

    Also, consider how much dilution air is being entrained into the baro. damper. Setting it more sensitive will drive down the draft but introduce more 'dry' air and possibly reduce sweating. You really only need about -0.01 to -0.02 wci in most equipment.
    I have tried completely blocking the baro damper off with a plastic bag. No difference.

    Last resort would be to pressure test the boiler to ensure it's not leaking into the combustion chamber. Note that things may leak when hot but not cold and vice versa but it's a start.
    Trust me, there are no leaks. I completely rebuilt this boiler.
    If you want a little entertainment, and have the time, read this: https://forum.heatinghelp.com/discussion/184643/flame-retention-head-conversion-of-wayne-e-series-burner/p1
    and https://forum.heatinghelp.com/discussion/185686/help-me-to-select-a-new-er-boiler-control-aquastat-for-my-old-boiler#latest
    I made little improvements over the years, and this shows how I got to where I am now.

    If the chimney is missing mortar allowing ambient air into the interstitial space around the flue liners that can cause excessive condensation, too.
    We will see - this spring/summer.

  • MikeAmann
    MikeAmann Member Posts: 422
    edited February 6
    From rockfordchimneysupply.com:
    Lifetime Transferable Warranty - The best warranty anywhere, transferable to new homeowner if you decide to sell. You're going to feel good about this purchase, plus you're adding value to your home.

    316Ti Stainless Steel Rectangle Chimney Liners - Air and water tight, with 7 ply seams and 10 corrugations per seam for the very best flexibility and strength on today's market. Rated number one in the industry for strength and flexibility. UL Listed and made of the highest quality, hand picked, prime stainless steel made in the United States.
    316Ti Liners - A unique titanium alloy designed to resist flue acids and the extreme stresses of hot and cold cycles. It can withstand multiple heating cycles up to 2100 degrees.

    To replace 7 in. diameter round liner (38 sq. in. cross section):
    For flue with inside dimensions 6 in. x 10 in.:
    Try one of the following options:

    Rectangle liner sizes:
    4.5 in. x 9.56 in. (37.88 sq. in. cross section), rectangularized from 7.5 in. round liner.**

    6 in. x 6.93 in. (36.87 sq. in. cross section), rectangularized from 7 in. round liner.

    5 in. x 9.06 in. (40.16 sq. in. cross section), rectangularized from 7.5 in. round liner.

    6 in. x 6.56 in. (34.79 sq. in. cross section), rectangularized from 6.5 in. round liner.

    4.5 in. x 8.43 in. (33.22 sq. in. cross section), rectangularized from 7 in. round liner.

    ** indicates closest match

    Oval liner sizes:
    6 in. x 9 in. (38.08 sq. in. cross section), ovalized from 7.5 in. round liner.**

    5.5 in. x 9.4 in. (36.30 sq. in. cross section), ovalized from 7.5 in. round liner.

    6 in. x 9.75 in. (41.39 sq. in. cross section), ovalized from 8 in. round liner.

    6 in. x 8.05 in. (33.88 sq. in. cross section), ovalized from 7 in. round liner.

    ** indicates closest match
  • captainco
    captainco Member Posts: 595
    My favorite way to address flue size opinions.
    Usually it is said that there is too much dilution air in a flue that is too big of a diameter, The I ask which has more air in it - a 10" flue 10 feet tall or a 6" flue that is 30 feet tall? If air is the problem does the 6" flue need to be shortened?

    You can be sure the people that wrote the flue sizing tables didn't write the duct sizing tables but then that is just me.
  • MikeAmann
    MikeAmann Member Posts: 422
    edited February 8
    @captainco
    Answer - the 6" x 30' tall flue has more air.
    Okay then, which set of guidelines should I follow?

    My old burner is now converted into what now amounts to a Beckett SR.
    Just like the SR, the blower fan and pump turn 1725 rpm.
    The rest of the parts are Beckett AF/AFG.
    I am using a .65 GPH nozzle at 120 psi which amounts to a .71 GPH firing rate.



    Would anyone that worked with these burners know what size the appliance breach had?
    I am guessing 6".
  • MikeAmann
    MikeAmann Member Posts: 422
    In my case, my boiler has a 7" breach, so I am required to maintain 7" pipe to the wall.
    Then the clay flue liner upsizes to 8" coming through the wall.
    See the pic below. Purple will be the SS tee. Would it be a good idea to use insulation between the two pipes (yellow)?

  • captainco
    captainco Member Posts: 595
    Unless the wall is combustible material it doesn't need insulation but it should be sealed with something. Unless the chimney is caving in there is no reason for a liner. When using flexible liners they always have to be one size larger than normal.
    A bandage doesn't heal a cut it just covers it up.
  • MikeAmann
    MikeAmann Member Posts: 422
    I sucked out another 2 gallons of flue gas condensation from my cleanout.
    It's like I took a garden hose and washed the clay liner down.
    Here is the sediment:

  • SuperTech
    SuperTech Member Posts: 1,792
    Wow that looks a lot worse than anything I saw with my chimney. I just had some flaking Terracotta in the top 3 or 4 feet. Is this debris from when you still had that chimney killer on your flue pipe?
  • MikeAmann
    MikeAmann Member Posts: 422
    @SuperTech
    I am so glad you saw this. I was going to ask if you were getting similar results.
    That sediment is from vacuuming the water out of the cleanout 2 times. 2 gallons each time.
    So 4 gallons in 1 month - the first 2 gallons was with the heat reclaimer still in place.
    I removed the reclaimer on Jan 7th. It was pulling some heat out of the exhaust.
    I think the condensation problem might be worse without the reclaimer because now there is more heat meeting the cold air in the clay flue. But still not enough heat to make it out of the top of the flue before condensation happens.
    With the reclaimer pulling some heat out, I believe I had cool exhaust meeting cold air >>> less condensation.
    But I am only guessing here.

    Let me step back a little bit.
    The reclaimer ran more with the low speed conventional burner head. And there was a good amount of soot to clean out each year. But no condensation problem that I was aware of.
    After converting to the flame-retention head, the reclaimer hardly ran at all. There is no soot now. And the breach temperatures were the same ~380 F in both cases (at the input to the reclaimer).

    I have my fingers crossed that after the clay flue pipe is done being "washed down", I will only have the water and no more sediment and terra-cotta flakes.
  • SuperTech
    SuperTech Member Posts: 1,792
    Seeing that much condensate is really alarming.  Perhaps the chimney was already in bad shape prior to the flame retention head conversion and now the more efficient flame isn't getting the stack temperature up enough before the boiler finishes its cycle. Have you been able to see what condition the terracotta liner is in? If outdoor air is infiltrating the chimney that's going to be the problem.  Does your burner run very short cycles? Gotta run long enough cycles to get that stack temperature up to avoid condensation. An insulated stainless steel liner has a lot less mass than the terracotta and will heat up faster.
  • MikeAmann
    MikeAmann Member Posts: 422
    edited January 24
    @SuperTech
    AFAIK, the chimney and clay flue is (was) solid.
    It needs to warm up a bit before I try to inspect.
    The outer brick and mortar joints are solid.
    The roof shingles were replaced this past summer.
    Could the roofers have messed something up with the new flashing?
    I suppose I could test that with the garden hose. Or maybe the leaf blower?
    If below 32 F outside, with a CFH, the burner will run 5 minutes on, 10 minutes off, repeat.

    Just thinking out loud here:
    The heat reclaimer has been in place for at least 10 years.
    Nearly all of that time with the less efficient conventional burner head.
    The reclaimer does pull some heat out of the exhaust.
    So I most likely had maybe 200 F going into the chimney.
    From what everyone is saying, this should have been the perfect recipe for condensation.
    But there was no condensation that I have ever seen.

    I completed the flame-retention head conversion going into THIS winter.
    That is when I noticed the water in the cleanout.
    The only other change was the roof.

    Crazy thought: could my 1965 house be so air tight that the burner pulls it's air supply DOWN the chimney flue? I did seal and insulate the rim joists. HUGE difference. If that were an actual problem, then it would have happened BEFORE the F-R head conversion because I had to cut back the burner's air band setting by ~75% to get to a trace of smoke with the F-R head.
  • MikeAmann
    MikeAmann Member Posts: 422
    I am doing an experiment.
    I found a little more water, but not another 2 gallons in the cleanout the other night.
    I started wondering what would happen if I left the door partially open.
    Would allowing some airflow there help or hurt this situation and which way would the air flow?
    So I fit a 2" thick piece of rigid foam board to the door opening with a 2-1/2" hole that fits my wet/dry vacuum hose. I ran the hose up and over to an empty 5 gallon bucket.
    I stuck my tongue at the end of the hose to test for airflow and direction.
    There is no cold air flowing out of the hose.
    And when the burner is running, air from the basement is flowing into the hose and up the chimney, hopefully aiding the draft in the chimney. I don't know if this means anything at this point, but I will give it a week to see what happens.

    I also increased the burner fan post-purge run time to 2 minutes.




  • SuperTech
    SuperTech Member Posts: 1,792
    edited January 29
    You want to keep the chimney tight and hot. Blowing a bunch of air up there isn't the answer, that will cool the chimney and add to the problem.  Minimize the post purge. That can cool the chimney and add to standby losses. Short cycles don't help either. Ideally you would want one or two long cycles per hour rather than several short ones. Long cycles minimize standby losses and lower wear and tear on components.  Unfortunately many boilers are oversized.  In my case even my downfired Peerless WBV-03 is a little bit more than I need. A buffer tank will eliminate the problem by reducing cycling and standby losses and keeping the chimney well above condensing temperature by the end of each cycle. 
  • MikeAmann
    MikeAmann Member Posts: 422
    @SuperTech
    I hear you and understand.
    This is just an experiment trying to gather ANY data to help me figure out why I find gallons of water in the cleanout. I will have a camera inspection done in the spring. I will turn the post-purge back down to just air out the combustion chamber after a burn. The heat reclaimer is no longer installed and I now have HOT exhaust going into the chimney. I should not be having this problem of rain inside the chimney now. If anything, I should have had the problem for the last 10 years. What I have happening now defies nearly everything that I am being told.
    If I decrease the firing rate, that will make LESS hot exhaust.
    If I increase the firing rate, then I will get even SHORTER burn times.

    When it is below 25 F outside with low humidity, there will be a near constant CFH from the hallway thermostat and the burner will run for 5 minutes ON, 10 minutes off. I don't know how I can increase the burner run time.

    I am using the ODR with the Hydrostat 3250+. I have an indirect water heater connected to the boiler. That is not in use right now (turned off). Here are my settings for the Hydrostat:
    • HL 205 (works best with my HW baseboards)
    • LL 132 (IWH set to 140. Has 8 degree DIFF. Don't want to cool the IWH.)
    • ECO 2.0 (ODR reset ratio of 2.0)
    THERMAL BOOST
    To insure that the heating system always satisfies a call for heat, the Fuel Smart HydroStat control is equipped with a thermal boost feature. If the thermostat is not satisfied thirty minutes after the boiler reaches the reset temperature, the control will boost the reset temperature by 10 degrees. It will continue to boost at 30 minute intervals until the call is satisfied. Once the call is satisfied, the control reverts to normal operation, utilizing the calculated reset temperature.

    If the target temperature has been boosted to the HI limit, then the differential automatically becomes 10 degrees.

    Is there anything I can do to get longer burner ON times? I see only 3 possibilities:
    1. Try different settings.
    2. Disable ODR and try thermal targeting instead.
    3. If that doesn't work, then turn off ECONOMY completely and run off of the HI limit and then I can select the differential.
    High Limit Differential
    When the Economy feature is on, the control’s Thermal Targeting feature actively sets varying differentials based on system conditions. This option allows for selecting a 10, 20 or 30 degree fixed differential when the Economy feature is turned OFF. These optional differential settings are subtractive from the HIGH LIMIT setting. Note: If the Economy feature is on, this setting will be overridden by the control's Thermal Targeting function.
  • SuperTech
    SuperTech Member Posts: 1,792
    The outdoor reset is a wonderful thing for fuel savings, so is the thermal targeting feature.  You have to make sure the curve is set is right and everything is setup to avoid short cycles. With an oil fired cast iron boiler you can only have a partial outdoor reset, you always have to keep the return water temperature high enough and the stack temperature high enough to avoid condensation. Make sure the stack temperature and return temperature get high enough at the low end of the reset curve. I go for a minimum boiler temperature of 155 degrees on mine. That works on my boiler.  

    Maybe you could use your indirect tank as a buffer tank to add the water volume needed to eliminate short cycles? A reverse indirect tank is an option.  Have you done a heat loss calculation to find out if your boiler is oversized or not? 
  • Bob Harper
    Bob Harper Member Posts: 914
    Get rid of that Magic Heat Reclaimer! On woodstoves those things are notorious for causing chimney fires. It is cooling your stack gases when you want the stack hotter!
    Every handful of terra cotta means that much less material up there that used to be your chimney liner. By code, it has failed and must be relined.
    Still waiting to hear on the Rh% of the CAZ and if you've pressure tested the boiler. Note that a boiler may not leak when cold but open up when hot.
    Correlate your weather with this problem- a chimney can store a huge amount of water. Need pics of the exterior chimney.
    Take a look at your heat exchange to the water- if too good, your stack will suffer. Pump speed, GPM, radiant surface, zones, etc.
    It's really simple- maintain net stack temp above dewpoint, reduce the condensing surface, and evacuate the smoke with a reasonable draft pressure and flow.
    Side experiment: check your water pipes. With everything 'off', do you still see movement in your water meter? Try it as long as possible but at least an hour or two. I've seen where a water pipe was leaking into a chimney undetected. Sounds crazy but you won't know until you've ruled that out.
    I'm still suspicious of the exterior of the chimney playing a role. Roofers are notorious for improper flashing. The crown and exterior surface are a water absorption & storage system.
    You've got a big boiler firing at a low rate. Just sayin'
  • Lance
    Lance Member Posts: 209
    Chimney design in 1980's was so lacking in our industry that BGE utility had to teach 10,000 contractors about chimney classes 1-4 and how to adapt to the new efficiency increases. A natural chimney is a unique device that balances between the building infiltration, the heat of the fire, and height and the termination point with regards to roof and wind. Traditionally we have to waste 20% of our combustion temperature to make a flue work properly. One main problem with flues is condensing combustion cannot work on a natural draft. The acidic condensate will quickly destroy it as well as prevent proper draft operation overfire. Size is critical to BTU input as well as design. If buoyancy of the draft is not established in 5-6 minutes it may fail to be approved. and in some cases poison the air in the home. the tighter the infiltration in homes the more we have to make sure the chimney will work especially when exhaust fans run, or a 2nd floor window is open. Building as well fuel gas codes are involved. If your at 400F with oil you may be too low when the gases reach the chimney top. Even the number of sides of a chimney exposed to outdoor air makes a difference in its performance especially if uninsulated.
  • MikeAmann
    MikeAmann Member Posts: 422
    edited January 31
    @SuperTech @Bob Harper @Lance
    Good info and suggestions guys. This is what I am looking for.
    "Something" that I changed caused this and I still believe that it has more to do with 1 change, rather than the result of a combination of smaller changes. I will try to make future posts to this thread in a before-and-after format for ease of comparison.
    Please keep checking this thread. I will post all findings and pictures. Hopefully your expert eyes will see what I don't. Believe me, whatever it is, it's staring us right in the face.

    Downside of Upgrades
    New furnaces hooked up to existing flues can result in condensation problems because they are more efficient than old models. While much of the heat produced by older heaters was lost out the flue, this heat prevented condensation by keeping the chimney or vent pipe warm so that air moved upward. Newer models keep most of the heat moving into the home, which results in a cooler flue. This means that the vapor has a much greater chance of cooling and condensing in the flue than it did with the old furnace.



    Bob Harper, the heat reclaimer has been removed since January 7th.
    The reclaimer was on there for about 10 years. That was before the flame-retention head conversion.
    At the time, I thought too much heat was being wasted going up the chimney. So this was a way to use some of that heat to warm the unheated basement. My boiler ran sooty all that time and had to be cleaned yearly. But I did not have a flue gas condensation problem, at least that I was aware of. Conventional burner with .85 GPH nozzle at 100 psi, 1725 rpm.


    After the conversion to the F-R head, the reclaimer was still in place and once I got the combustion numbers dialed in, the reclaimer ran much less often than it did before the conversion. So much less that I thought it wasn't worth having it in there any more. The reclaimer has it's own built-in thermostat and cycles on and off automatically. I was able to achieve ZERO smoke with the F-R head conversion. Now running a .65 GPH nozzle at 120 psi = .71 GPH firing rate, still 1725 rpm. Now I have essentially a Beckett SR burner. I have a clean, more efficient flame that uses less fuel to put out the same amount of heat.
    But I was now able to stick my hand in through the barometric damper (after the reclaimer) with the burner running and I felt warm air (guess 125 F). I could keep my hand there all day without getting burnt, even though the flue gas temp at the breach (input to reclaimer) was ~380 F.
    This is when I first found the 2" of water in the cleanout.

    After I removed the reclaimer, with the burner running, I can't even touch the pipes for more than 1 second without getting burned. THERE SHOULD BE NO CONDENSATION NOW! The barometric damper remains closed at the minimum setting. The pipes are hot all the way to the chimney.

    This is me thinking aloud: I haven't made a measurement, but the draft should have increased by removing the reclaimer. So now I have the necessary hot flue gas temperature, just not enough volume to carry that heat to the top of the chimney before it condenses.

    After this last batch of comments, my money is on this:

    Best original baffle.


    Comparison of original baffle and new stainless steel baffles.


    New SS baffles installed. Ran like this for about 4 years with the reclaimer in place.
    I thought the "tongues" were too small (not restrictive enough) for the F-R head conversion.
    The hot flue gas needs to wipe the cast iron tube better to transfer more heat into the water.



    I added these pieces on to make the tongues bigger.



    But I went too big. I had to sand some off (red line).



    Comparison of original baffle and the SS baffle with the extra added. Too much added.


    The difference between the two.


    What I plan to sand off.


    Sanded down to allow more flue gas flow.


    Modified SS baffle installed in tube. Still too restrictive?

    Bob Harper, I will have more for you. This is enough for right now. One step at a time.
    If you want to see how I got to this point, start here: https://forum.heatinghelp.com/discussion/184643/flame-retention-head-conversion-of-wayne-e-series-burner/p1
    Plenty of pictures - you wouldn't have to read a lot. ;)
  • MikeAmann
    MikeAmann Member Posts: 422


    1. Still waiting to hear on the Rh% of the CAZ and if you've pressure tested the boiler. Note that a boiler may not leak when cold but open up when hot.

    2. Correlate your weather with this problem- a chimney can store a huge amount of water. Need pics of the exterior chimney.

    3. Take a look at your heat exchange to the water- if too good, your stack will suffer. Pump speed, GPM, radiant surface, zones, etc.

    4. It's really simple- maintain net stack temp above dewpoint, reduce the condensing surface, and evacuate the smoke with a reasonable draft pressure and flow.

    5. Side experiment: check your water pipes. With everything 'off', do you still see movement in your water meter? Try it as long as possible but at least an hour or two. Sounds crazy but you won't know until you've ruled that out.

    6. I'm still suspicious of the exterior of the chimney playing a role. Roofers are notorious for improper flashing. The crown and exterior surface are a water absorption & storage system.

    7. You've got a big boiler firing at a low rate. Just sayin'
    I can answer some of these questions right now @Bob Harper:

    1) Relative Humidity in basement is 50%. The condensation happens in the chimney flue from completely dry and frigid outside to raining. What is CAZ? Pressure testing the boiler? You mean the water tank or the combustion chamber? I can tell you right now that there isn't even 1 drop of water leaking anywhere. I leave the autofill off because I have a LWCO. The tankless coil does not leak a drop, or it's gasket. And I know the combustion chamber is tight. I went to great lengths to make sure when I replaced the ceramic chamber. The chamber is supported on the bottom and is not able to slide down, creating a gap and then the telltale burn marks on the side sheet metal. Please look here: https://forum.heatinghelp.com/discussion/184643/flame-retention-head-conversion-of-wayne-e-series-burner

    2) Pictures of the chimney will be coming.

    3) My heat exchange to the water may be too good. But I do get a 400 F temperature at the breach.

    4) I may not have enough hot flue gas flow. The baffles could still be too restrictive.

    5) I did the water meter test. The gauge didn't budge one bit. No dripping faucets or leaking toilets either.

    6) Chimney pics coming.

    7) Boiler nameplate ratings: Gross 115. M Net 103.5 M Max Input Oil GPH 1.10
    This conventional burner always ran with a .85 GPH nozzle. I am now at a .71 firing rate with the new F-R head.


    And one for you @SuperTech - you always have to keep the return water temperature high enough and the stack temperature high enough to avoid condensation. Make sure the stack temperature and return temperature get high enough at the low end of the reset curve. I go for a minimum boiler temperature of 155 degrees on mine. That works on my boiler.

    So you are saying that my heating loop could be losing so much heat that the return water temp is so low that it cools the boiler into the condensing range, correct?
    I used my infrared temperature gun tonight while there was a CFH and the circulator was running. 191 F at the output pipe - 181 F returning. As you already know, I have the Hydrostat 3250+ control. It does not allow the circulator to run below 125 F. My LL is set to 132. I could increase that setting. But I still get the rain while running off my HI limit of 205 F.
  • Lance
    Lance Member Posts: 209
    Wow Bob. You are not a homeowner with a heat problem you are a manufacturer working on designing a modified boiler to test the results. You are going through all the results an R&D lab does to make a new combustion system. There are a lot of hard learned lessons that come with the design of a combustion system. Several major manufacturers I know had serious and deadly results bringing some products to market, only to learn their lab results are not the same as the locations they end up in. Faulty engineering cost tons of money and the designers are not always caught paying for it. They instead blame the owners, the installers, the application, the operator. I have confronted some of them and proved their product and only their product was the problem. I have seen their lies mad public for years until they apologized for the problems they blamed on others. When millions of dollars in warranty is at stake anything can happen. It pays to be expert in any field dealing with electric and fuel. I am not here to bash anyone, but to urge all to be very careful when modifying designs. Public schools don't teach real life history from the home standpoint much anymore except for "DAN" but the lessons are there as well as the costs of life and property. Modifying any heat exchanger can be done, but not without consequences/ offsets. We think it will be positive & only see the part we look for and fail to measure over time the things that can be negative. I never truly understood the combustion chamber until I asked how it was designed. I never knew how smoke kept getting in my face no matter where I stood around a camp fire until someone told me my body acted like a chimney riser. Laws of physics cannot be broken but that doesn't stop many from trying. I wish I had known all the modifications you made before my first comment. You reminded me not to give advice until all the facts are known. Thank you and good luck, Lance. PS since you are still alive I believe you are very capable in your task at hand.
  • Lance
    Lance Member Posts: 209
    One last comment. Flue gas dewpoint is a function of temperature and % RH. See here: https://www.engineeringtoolbox.com/dew-point-flue-gases-d_1583.html When condensing occurs in a combustion chamber at or near the breach, the humidity is very high enough to condense especially on a cold startup. Steam at atmosphere boils at 212F. So approaching 212F and below along any flue surface acidic condensate will occur. Two solutions are possible when close to the dew point. Maintain the temperature high enough to reach the flue termination or add insulation to prevent temperature drop or a little of both.
  • captainco
    captainco Member Posts: 595
    edited February 1
    I love those Dew point charts and wonder how they related to combustion gases versus weather dew points. Flue gas consists of O2 but mostly CO2. I am pretty sure the dew points of flue gas are not any where near what these fabricated charts indicate.

    In the 80's I sold the first recuperative furnaces. The lowest flue temperature on the smallest furnace was 180 degrees and the largest was 210 degrees, They all condensed! I sold condensing oil furnaces that had 140 degree flue temperatures and they all condensed. The charts on Engineering toolbox don't agree.

    Hydrogen in the fuel is converted to water and then steam. Steam changes to water below 212 degrees. I am pretty sure mod-con boilers are still condensing with 180 degree flue temperatures.

    Oil which contains less hydrogen than natural gas condenses at lower temperatures in the field than gas, The charts don't agree. One thing I learned 40 years ago is that the field has a mind of its own and only field testing confirms data. What other charts or graphs are simply mathematical calculations versus actual field verification.

    Duct sizing charts, combustion air charts, venting table charts, blower performance charts and combustion efficiency charts to name a few.
    Blasphemer, heretic, loose canon etc. Just a few of my names over the years.
    SuperTechLarry Weingarten
  • Bob Harper
    Bob Harper Member Posts: 914
    Jim, I think you left out: lunatic, psycho, troublemaker, maniac, rogue and a few other compliments I can't mention here but I can post the other names: genius, innovator, legend, and authority. Great chatting with you today old friend.
    captaincoSTEVEusaPALarry Weingarten
  • MikeAmann
    MikeAmann Member Posts: 422
    edited February 4
    SuperTech said:

    The outdoor reset is a wonderful thing for fuel savings, so is the thermal targeting feature.  You have to make sure the curve is set is right and everything is setup to avoid short cycles. With an oil fired cast iron boiler you can only have a partial outdoor reset, you always have to keep the return water temperature high enough and the stack temperature high enough to avoid condensation. Make sure the stack temperature and return temperature get high enough at the low end of the reset curve. I go for a minimum boiler temperature of 155 degrees on mine. That works on my boiler.  

    I'm thinking about this. My old Honeywell aquastat and Intellicon HW+ fuel economizer allowed me to essentially have as much as a 60 degree differential from the Hi Limit which was 200 F at the time. So the boiler would heat to 200 and the water would circulate until the temperature got down to what the HW+ determined to be the target temperature to match the heat loss. Then allow the burner to fire. The burner would run longer because it had to heat from as low as 130 back up to 200. No short cycles.
    I will describe this as controlling from the top (hi limit) down. The house came up to temp a lot quicker using this method.

    The new Hydrostat 3250+ works opposite - from the bottom up. It keeps slowly raising the target temperature until the heating matches the heat loss. When it is really cold, the Hydrostat will get to where it is running off the High Limit and it's 10 degree fixed differential. So the circulator is running the entire time, the burner heats to 205, and it takes 10 minutes for the water temperature to drop 10 degrees. Fire the burner again and it only runs for 5 min back to 205. Lather, rinse, repeat. The house takes forever to heat up and satisfy the CFH using this method.

  • MikeAmann
    MikeAmann Member Posts: 422
    I switched outdoor reset to warm weather shut down only so I can give thermal targeting a try. I have 1 heating loop for the whole house, so I selected "1" for a 1 zone heating system.

    I have seen that ODR works "from the bottom up". I am unsure if Thermal Targeting works the same way, or "from the top down". If this doesn't give me what I need, then I can turn ECONOMY off and run off the High Limit with a 30 degree differential. That will increase the burner run time.
    I also bumped the Lo Limit up to 140.
  • MikeAmann
    MikeAmann Member Posts: 422
    edited February 5
    @Lance
    Lance said:

    I wish I had known all the modifications you made before my first comment. You reminded me not to give advice until all the facts are known.

    Please keep your comments coming - they are helpful.
    That goes for everyone else too. The help is appreciated!

    Bob Harper is not the psycho doing all this R&D work to this old boiler >>> I am.
    Nobody has to worry about trying to help me figure this out - it is my hands doing the work and the only one accountable IS ME.

    Whether my chimney is compromised or not, I like the idea of a SS liner and plan to install this year. But first I must figure out what is causing this huge condensation problem. Otherwise I will have spent $$$ on lining the chimney AND STILL HAVE THE SAME PROBLEM.

    Bob Harper summed it up very nicely - It's really simple- maintain net stack temp above dewpoint, reduce the condensing surface, and evacuate the smoke with a reasonable draft pressure and flow.
    ……
  • MikeAmann
    MikeAmann Member Posts: 422
    edited February 6
    @BobHarper
    Bob, you said this: ..... should be a ss liner swept into the room or with a tee at the base as a condensate trap or ss wye in the Combined Venting thread.
    I have 1 simple (hopefully simple) question relating this to my situation:
    I agree with installing a SS liner, and I actually am now loving the idea.
    Doing so will stop any further deterioration to the masonry.
    Because my clay flue is rectangular 6" x 10", I will be forced to use ovalized smooth wall heavy gauge 316Ti stainless liner. My breach is 7" and I must maintain that size to the wall. But the chimney liner CAN be downsized by 1 size to 6". To have 1/2" clearance to the terra cotta tiles, that means the ovalized pipe would need to be 5" x 9". The pipe areas work. 6" round = 28.27 sq in. 7" round = 38.48 sq in. And 5" x 9" oval = 35.34 sq in, just slightly less than the area of 7" round. I will have that custom made.
    Code says that liners for gas and oil are not required to be insulated. This will give me the insulated Thermos bottle you described: Actually, if you block off the air at the top and base it is air insulated, much like a Dewar's Flash (Thermos Bottle).

    ..... a high mass liner, such as terra cotta, absorbs more BTUs than a thin-walled corrugated liner. No longer will I have to worry about trying to heat up a huge mass of masonry to prevent condensation.

    And because the liner will not be in contact with the clay liner, the SS liner will heat up much faster and my draft should increase (warm chimneys can maintain a stable draft long term better than cold ones). The flue gas should now be able to make it all the way out of the top of the chimney before condensation occurs.

    So my question is:
    Weather conditions vary greatly. Suppose I did get a little condensation after the new SS liner was in place. It wouldn't matter any more because now there would be no damage to the masonry, correct?

    Thanks, Mike.

    If I am understanding this correctly now, it means that you guys are great teachers!
  • Bob Harper
    Bob Harper Member Posts: 914
    One of the purposes of installing a ss liner, even on brand new masonry chimneys, is to convey the byproducts of combustion and contain any condensation. Terra cotta fails at this miserably, which is why we have cleanouts- for planned failure. You do not need a cleanout on a ss liner except for solid fuel. However, a tee or wye will act as a sump for condensate. The wye will provide good access for inspection and maintenance. If the liner is 316L or 316Ti it should be able to withstand the corrosive effects of condensation. It is certainly better than the mortar between flue tiles, which is alkaline. Acid + base > salt + water. Flue gases convert your flue tile mortar into sand and salt water.
    Why can't you post current draft, CO and O2 readings? No sense worrying about this any further until you have that info.
    STEVEusaPASuperTech
  • MikeAmann
    MikeAmann Member Posts: 422
    edited February 7
    @Bob Harper
    You must have missed these.

    I do not have access to the combustion analyzer at the moment. Maybe not again.

    These results have the same setup as I am currently running.
    The only difference is that the heat reclaimer is now removed.
    The flue gas going into the chimney is now much hotter because the reclaimer is not sucking the heat out.
    I should have had the condensation problem with the reclaimer installed, not now.
    I discovered the water in the cleanout AFTER the reclaimer was removed.
    Draft is -.020 over the fire and -.025 in the breach. .65 GPH hollow nozzle at 120 psi giving a .71 GPH firing rate.


    I want the tee so that I can extend pipe down to my cleanout door simply for inspection and to see if I still get any condensation after the liner is installed. I want to be able to see from top to bottom. That's it.

    I now have a condensation problem. All I am trying to do is pinpoint why.
    AFAIK, I did not have this problem before the F-R head conversion.
    I am very confident that I do not have a boiler problem.
    I am very confident that I do not have a burner problem.
    The way I see it, what I have is a cold exterior masonry chimney full of cold air. Did I mention COLD?
    Now that my burner is so much more efficient, I have less hot exhaust going into the chimney than before.
    BEFORE, with the reclaimer, I had cool meeting cold in the chimney, and no condensation.
    Now I have hot meeting cold which is creating a rain storm = condensation.
    I simply do not have enough hot exhaust to heat all of that masonry and make it all the way to the top and out of the chimney before condensation occurs. A SS liner should solve this problem, increase my draft numbers, and my combustion numbers will probably get better too.

    The chimney pictures will be posted within the next 2 days.
  • captainco
    captainco Member Posts: 595
    This furnace is really underfired, There should be a ,02" draft difference at the outlet versus the over fire. This is the design pressure drop of an oil furnace heat exchanger when fired correctly. Actually efficiency is more likely in the 60 percent range.
  • MikeAmann
    MikeAmann Member Posts: 422
    edited February 8
    @captainco
    I will agree with the draft difference.
    Really underfired - not so much.
    As long as I have owned this house (and before), the nozzle was always .85 GPH.
    Now .71 firing rate. That's only a 16.5% difference.
  • MikeAmann
    MikeAmann Member Posts: 422
    Chimney pictures:















  • SuperTech
    SuperTech Member Posts: 1,792
    edited February 8
    @MikeAmann I would definitely follow any advice given by @captainco
    He's probably the most knowledgeable expert on all things combustion related that you will find.  
  • MikeAmann
    MikeAmann Member Posts: 422
    I have found Strictly Chimneys just 1 town up the road from me in Berlin, CT. https://strictlychimneys.com/
    Does anyone here have anything (good or bad) to say about them?
    I plan to contact them about a video inspection and possibly breaking out the clay flue so that I can install a proper SS insulated liner.
    Thanks, Mike.