: McGiever On: Sun Dec 30, 2012 8:06 pm
Is that not what the hysteresis does?
Generally once the ash temps start going up they can go up quickly so the difference between a 5dg and a 10dg hysteresis may be only couple of strokes (more or less) on the grate. So the hysteresis can control ashing time to a degree.
Just an observation:
Often after a long idle time the ash layer becomes a little thicker and cooler, not yet quite cool enough to call for ashing, the idle fire is smaller as well. (note that I have never measured ash thickness but long ashing cycles generally follow long idle times)
Then there is a call for heat and the fan comes on, the cool air goes thru the now thicker ash layer and can drop it easy 30+- dg below SV, the boiler gets up to temp and the fan turns off but the ash has not reached SV so it keeps putting more new coal on a now hot but idle fire (insert puff back here?) until SV is reached.
The ashing scenario during a more active period seams to not drop ash temps as drastically as after a long idle and will return to SV much faster.