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Central heating boiler - bricking of the grate with a part of the grate.

Xantix 15648 14
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  • #1 16740535
    Xantix
    Level 41  
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    Hello. I am dealing with a certain central heating boiler and I have a problem with it - it is massively oversized. I decided to reduce his walling up part of the grate with chamotte. And my question is: do I have to brick up half of the grid to reduce the boiler's achievable power? Is this relationship not linear?
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    #2 16740746
    Magister_123
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    Is the dependence is linear, I do not know, but I modernized my boiler. From my experience, instead of using a chamotte mortar, use ash to transfer the bricks. This method is to each other that you can add and subtract bricks at any time. After the season, when you sense the cauldron then you can be tempted to glue the whole.
    What kind of boiler do you have? Śmieciuch?
  • #3 16740753
    Xantix
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    Magister_123 wrote:
    What kind of boiler do you have?

    This is not my boiler. I would choose it according to the demand, but unfortunately the owner of the boiler did not let me convince, he only entrusted the installer with "specialists" who pressed him for a large boiler 2x. And now this hot potato was thrown at me.

    Magister_123 wrote:
    Śmieciuch?

    It's a normal upper combustion boiler, a local manufacturer.
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    #4 16740821
    Magister_123
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    If you're having so much fun, add the secondary air steering wheel. As is the place, it is still the draft regulator.
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    #5 16741042
    jack63
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    After this modification, the exhaust temperature will drop. You need to take care of the chimney. It is about patency, cross-section and possibly insulation, because there may be problems with the string.
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    #6 16741159
    Sstalone
    Level 31  
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    Xantix wrote:
    Hello. I am dealing with a certain central heating boiler and I have a problem with it - it is massively oversized. I decided to reduce his walling up part of the grate with chamotte. And my question is: do I have to brick up half of the grid to reduce the boiler's achievable power? Is this relationship not linear?


    I have been lecturing the boiler for the last time, so I can say that the power not only depends on the cross section of the air supply ducts, but also on the exhaust gases. The best way was suggested by a colleague Magister_123, I myself did everything undressed ... it all depends on the design of the boiler.

    However, as for the chimney, even if we reduce the boiler's power and the temperature of the fumes will be lower, but the fumes will be better burned, the question is whether it will not be better for him.
  • #7 16741205
    Xantix
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    jack63 wrote:
    After this modification, the exhaust temperature will drop.

    And it will be beneficial in this case.

    jack63 wrote:
    You need to take care of the chimney.

    In this case, I think there is no need. This boiler has a tragically small convection exchanger and now the temperature of the exhaust fumes can be approached 350 degrees with such burning. Simply a tool for heating the atmosphere. I think that the temperature of the exhaust should not fall below 200 degrees after this transformation.

    Magister_123 wrote:
    If you're having so much fun, add the secondary air steering wheel. As is the place, it is still the draft regulator.

    Both are already there. Unfortunately, unfortunately only a decent boiler in the boiler is missing.
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  • #8 16741248
    jack63
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    Xantix wrote:
    This boiler has a tragically small convection exchanger and now the temperature of the exhaust fumes can be approached 350 degrees with such burning. Simply a tool for heating the atmosphere. I think that the temperature of the exhaust should not fall below 200 degrees after this transformation.

    And that's sorry. I thought it was some decent boiler, and it looks like crap.
    Unfortunately, my opinion about Polish boilers is confirmed. :cry:
    I wonder what is the comedian and how does his interior look after such a ride ???
  • #9 16741596
    Xantix
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    jack63 wrote:
    I thought it was some decent boiler, and it looks like crap.

    No crap in the production of a local producer Made in garage, where it can be made of 100 cauldrons a year, so there is nothing to expect high quality since a welder does not make a boiler.

    jack63 wrote:
    Unfortunately, my opinion about Polish boilers is confirmed. :cry:

    Is not so bad. A lot of models of Polish boilers are very good quality products. The problem is mainly the products of garage manufacturers, which are patched with metal boxes without any professional knowledge. I drive alone on the MPM DS boiler and it is a very successful construction.

    jack63 wrote:
    I wonder what is the comedian and how does his interior look after such a ride ???

    Chimney with clinker. The interior is covered with a few millimeter of powdery creamy brown soot. There is usually no need to clean - everything evals ...
  • #10 16742209
    andrzej lukaszewicz
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    jack63 wrote:
    After this modification, the exhaust temperature will drop. You need to take care of the chimney. It is about patency, cross-section and possibly insulation, because there may be problems with the string.

    Or maybe the opposite. On the oversized, the temp lowers and the boiler suffocates at 45 degrees. After reducing the furnace (and power) you will be able to smoke at 65 degrees and the exhaust will be hot.
  • #11 16742413
    Sstalone
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    andrzej lukaszewicz wrote:
    jack63 wrote:
    After this modification, the exhaust temperature will drop. You need to take care of the chimney. It is about patency, cross-section and possibly insulation, because there may be problems with the string.

    Or maybe the opposite. On the oversized, the temp lowers and the boiler suffocates at 45 degrees. After reducing the furnace (and power) you will be able to smoke at 65 degrees and the exhaust will be hot.


    Yes, but on condition that the power consumption with CO will be reduced by lowering the temperature of the water behind the boiler.

    I have a question, is it more beneficial to lay out the furnace of a solid fuel boiler with thin or thick chamotte elements? Thin heat up quickly, thicker longer keep the temperature that burns up better?
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    #12 16744055
    andrzej lukaszewicz
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    This is about the physical reduction of the hearth, not the accumulation of the fireclay.
  • #13 16745838
    Sstalone
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    andrzej lukaszewicz wrote:
    This is about the physical reduction of the hearth, not the accumulation of the fireclay.


    The problem to be solved is to reduce the boiler's power, the proposed solution is to wall the grid parts, but when changing the boiler structure, do not forget about better combustion of fumes with reduced boiler power (the flue gas temperature naturally decreases). The question was whether to use thinner or thicker chamotte pieces in the construction to burn out the exhaust? A separate issue is the way they are built.
  • #14 16745887
    stanislaw1954
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    Sstalone wrote:
    . The question was whether to use thinner or thicker chamotte pieces in the construction to burn out the exhaust? A separate issue is the way they are built.
    And how do chamotte tiles (thicker or thinner) burn off? is it the equivalent of a turbo in a diesel engine?
    This is only about reducing the combustion chamber in the boiler, i.e. less coal can be disposed once. And by filling partially, for a large chamotte combustion chamber, we also extend the thermal inertia of the boiler, because after burning the coal, the boiler will keep warm for a little longer.
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    #15 16745919
    andrzej lukaszewicz
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    The use of fireclay in the burning place (burner) isolates the flame from the "cold" water jacket, which causes an increase in the combustion temperature and, therefore, a better burn-up. The topic is more to lower combustion boilers due to their construction than to the upper one (most common constructions of craftsmen and large producers too).
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Topic summary

✨ The discussion revolves around the challenges of managing an oversized central heating boiler, specifically regarding the modification of the grate using chamotte to reduce its power output. Users share experiences and suggest that the relationship between grate modification and boiler power is not linear. Recommendations include using ash for brick placement to allow for adjustments, ensuring proper chimney maintenance, and considering the impact of exhaust gas temperatures. The conversation also touches on the effectiveness of different chamotte thicknesses in enhancing combustion efficiency and the importance of boiler design in achieving optimal performance.
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FAQ

TL;DR: To tame an oversized upper-combustion boiler, brick off part of the grate with firebrick; Xantix reports flue gas ~350°C and targets >200°C, noting it was “simply a tool for heating the atmosphere.” [Elektroda, Xantix, post #16741205] Why it matters: Reducing the active hearth cuts output, stabilizes burn, and helps avoid cold, sooty operation for users stuck with an overpowered unit.

Quick Facts

Is power reduction linear with the amount of grate I brick up?

Not strictly. Boiler output depends on more than grate area; air supply and flue‑gas paths also govern burn rate and transfer. Adjust in stages and observe flue temperature and draft. As one expert put it, power depends on both air inlets and exhaust passages, not just size. [Elektroda, Sstalone, post #16741159]

How much of the grate should I block off first?

Start reversible. Dry‑set a small section of bricks with ash, fire the boiler, and check room heat, return temperature, and flue draft. Add or remove bricks until cycling and soot decrease. When stable, make it permanent. “You can add and subtract bricks at any time.” [Elektroda, Magister_123, post #16740746]

Will flue‑gas temperature drop after I reduce the hearth?

Yes, expect a drop, which can cut draft. Confirm the chimney is clean, properly sized, and, if needed, insulated to preserve pull. Poor draft is a common failure mode after heat‑exchanger or firing‑rate changes. [Elektroda, jack63, post #16741042]

What flue temperature should I aim for after the modification?

In the cited case, the boiler ran near 350°C; after reduction, the target was above ~200°C to avoid weak draft and condensation. Track with a probe thermometer during steady burn. [Elektroda, Xantix, post #16741205]

Does fireclay (chamotte) lining actually improve combustion?

Yes. Fireclay around the burner shields the flame from the cold water jacket. That raises flame temperature and improves burn‑out of volatiles and CO. “Isolation causes an increase in the combustion temperature.” [Elektroda, andrzej lukaszewicz, post #16745919]

Should I use thin or thick chamotte pieces?

Thicker pieces add thermal inertia, so the boiler stays warm longer after fuel burns out. Thin pieces heat quickly but store less heat. Choose thickness based on response time versus heat retention needs. [Elektroda, stanislaw1954, post #16745887]

How do I add secondary air or a draft regulator to clean up the burn?

Install an adjustable secondary air inlet above the fuel bed and a mechanical draft regulator on the flue. Tune both while monitoring smoke and flue temperature. These additions help stabilize an oversized unit. [Elektroda, Magister_123, post #16740821]

My oversized boiler "suffocates" at 45°C. Will the mod help me run hotter?

Yes. Reducing hearth size increases load matching, letting you run around 65°C without choking the fire. Hotter operation also raises flue temperature and reduces wet soot. This shift improves efficiency and comfort. [Elektroda, andrzej lukaszewicz, post #16742209]

Any quick, reversible method to test different hearth sizes?

Yes—use ash as the bedding material for the bricks. It grips well, tolerates heat, and lets you reconfigure the layout in minutes during trials. Mortar later if the setup proves out. [Elektroda, Magister_123, post #16740746]

Could a small convection exchanger limit my gains?

Yes. A constrained exchanger can force very high flue temperatures and waste heat despite hearth reduction. One case ran ~350°C flue gas due to poor exchange. Aim to improve heat transfer surfaces if feasible. [Elektroda, Xantix, post #16741205]

What’s an example of a well‑behaved solid‑fuel design to benchmark?

Users reported good results with the MPM DS line, noting it as a successful construction relative to garage‑made units. Use such references to set expectations for stability and cleanliness. [Elektroda, Xantix, post #16741596]

Will chimney fouling change after the modification?

Expect differences. One installer saw a thin, powdery, cream‑brown soot layer that sheds easily with certain setups. Inspect after changes and establish a new cleaning interval to maintain draft. [Elektroda, Xantix, post #16741596]

Any edge cases I should watch for after reducing boiler power?

If flue temperature falls too low, draft can collapse, causing smoke‑back and CO risk. Verify chimney cross‑section, height, and insulation, and monitor during cold starts and low fire. [Elektroda, jack63, post #16741042]

How do I trial and finalize a grate‑reduction layout?

  1. Dry‑fit chamotte bricks on the grate using ash as the bedding.
  2. Fire the boiler, monitor flue temperature and room heat; adjust brick count.
  3. Once stable, rebuild the layout permanently if desired. [Elektroda, Magister_123, post #16740746]
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