FAQ
TL;DR: Start around 40% fan and 8 s feed; "70% turnover is definitely too much." Then fine‑tune pause and draft to stop a hot chimney. This FAQ helps 25 kW coal‑boiler owners fix poor burn and reduce fuel waste. [Elektroda, hajtaler, post #17538465]
Why it matters: Clear starting points and draft fixes solve hot‑chimney, overfeeding, and slaking issues fast for feeder coal boilers.
Quick Facts
- Start-point for manual tuning: blower ≈40% and feed ≈8 s; change feed by 1 s steps while watching the fuel mound. [Elektroda, hajtaler, post #17538465]
- Example heat load: 150 m² home needs max 15.5 kW at −20°C and averages 7.3 kW. [Elektroda, boczek29, post #17538141]
- Overdraft signs: hot chimney, air drawn through a stopped fan; add a closing flap and seal the hopper lid. [Elektroda, Anonymous, post #17536962]
- Hardware aids: fit a chimney draft regulator and a non‑return flap on the fan inlet. [Elektroda, korystor, post #17537660]
- Fuel quality matters: a bad coal batch may not burn well even with correct settings. [Elektroda, kriso221, post #17536993]
What are good starting feed, pause, and fan settings for a 25 kW screw‑feeder boiler?
Drop the blower to about 40% and set feed near 8 seconds. “70% turnover is definitely too much.” Observe the fuel mound. If it flips forward, shorten feed by 1 second and recheck. If the mound collapses, lengthen feed slightly. Keep your current pause initially, then tune it last. This stabilizes combustion and cuts waste. [Elektroda, hajtaler, post #17538465]
Why is my chimney hot, and how do I fix overdraft?
Excessive chimney draft can pull air through the fan even when it’s stopped, overheating the flue. Fit a flap that closes the fan inlet when off. Check the coal hopper lid and seals for leaks. Air entering via the reservoir can cause heat return through the feeder. Reduce uncontrolled air, then re‑tune feed and fan. [Elektroda, Anonymous, post #17536962]
Why does lowering fan speed make the fire go out or push coal out?
When you cut air, you must also cut fuel. Reduce feed time together with blower speed. If you only lower air, the bed cools and slakes. If you only lower feed, the mound may collapse. Tune in small steps and observe the bed shape and flame. [Elektroda, hajtaler, post #17538465]
Are 13 s feed, 58 s pause, and 70% fan reasonable?
The fan is too high. Lower it to about 40% and re‑check combustion. Shorten feed by small steps if the mound flips; lengthen if it sinks. Keep your existing pause until air and feed stabilize. Then trim pause to stop unburned push‑out. [Elektroda, hajtaler, post #17538465]
Do I need a chimney draft regulator or a non‑return flap?
Yes. Install a chimney draft regulator to tame excessive draft. Use a non‑return flap on the fan so the inlet closes when the blower stops. These two items stabilize air supply and protect the feeder. [Elektroda, korystor, post #17537660]
How much does fuel quality affect burn stability?
A lot. Different coal batches behave differently. Poor batches may not ignite cleanly or sustain a stable mound, even with good settings. If switching suppliers changes results, re‑tune air and feed, or change fuel. [Elektroda, kriso221, post #17536993]
What info should I share to get useful tuning help?
Provide boiler make and model, heated area in m², controller type, fuel type/class, and current settings. Photos of the burner and ash drawer help diagnose air distribution and burn quality. Include recent cleaning status. [Elektroda, internick, post #17537689]
Is my 25 kW boiler oversized if my home’s max demand is 15.5 kW?
Yes, it’s significantly oversized. Your calc shows 15.5 kW peak and 7.3 kW average. Oversizing causes cycling, hot flue, and poor efficiency. Mitigate by reducing air, shortening feed, and stabilizing the fire bed to match actual load. [Elektroda, boczek29, post #17538141]
Is a hot chimney always bad?
Not necessarily. A warm flue can be better than a very cold one that tars up. Very low exhaust temperatures promote condensate and tar. Balance by controlling draft and air while keeping clean combustion. [Elektroda, internick, post #17538089]
How do I manually tune a feeder boiler fast? (3‑step)
- Set blower ≈40% and keep your current pause.
- Set feed ≈8 s, then adjust by 1 s watching the mound.
- When the mound stays stable and ash is gray, trim pause to prevent unburned push‑out. [Elektroda, hajtaler, post #17538465]
How can I check airflow and sealing on the burner?
Inspect the burner crown and front for ash build‑up that looks like cauliflower. Ensure passages are open and seals intact. Confirm the boiler and chimney are recently cleaned. Uneven deposits and leaks indicate poor air distribution or overdraft. [Elektroda, internick, post #17538089]
Should I try automatic PID mode on my controller?
Yes. Switch to automatic mode and let the controller choose parameters to hit your setpoint. Observe behavior and ash quality. If results improve, keep auto; if not, return to manual and tune as above. [Elektroda, internick, post #17538218]
What fuel consumption signals overfeeding?
An example calculation showed roughly one scoop per minute, about six buckets per hour, equating to about 120 kWh/h of fuel energy. That rate is excessive for typical residential loads and indicates overfeeding and overdraft. Reduce air and feed, then reassess. [Elektroda, Anonymous, post #17538347]
Can I burn eco‑pea coal in an old 17 kW Ogniwo without a feeder, top‑down with wood?
Only if the boiler’s manual explicitly allows that fuel and method. Follow the manual’s fuel list and setup guidance. If it doesn’t approve pea coal or top‑down lighting, do not do it. “The boiler manual provides optimal presets and correction methods.” [Elektroda, Anonymous, post #17536962]
How do I prevent heat returning through the feeder?
Seal the hopper lid and check its gasket. Fit a flap that closes the fan inlet when the blower stops. Excess draft can pull air through the fan or reservoir and route heat back into the feeder. Fix leaks, then re‑tune. [Elektroda, Anonymous, post #17536962]
