What does it mean in the Axeman-Anderson manual when it says that: "Fire too thick may cause puff-back"
Thick fire = Low Fire
Thin fire = High Fire
Axeman's manual has been around for a long time and uses different terminology than AHS.
There are three sections in the fire-tube basically...the raw coal layer, the fire layer and the ash layer. They are not totally distinct sections, but for adjustment purposes that is how they are described.
When the fire is thick
then the ash would be thin
and vice versa. In the thick fire case the ashing setting would be too high and need to be lowered.
To take this a step further...(this was mentioned earlier) a thick fire has consumed most of the oxygen deeper in the fire bed plus a quantity of raw coal has just been added on top and is out-gassing volatiles,so with the lack of oxygen in the upper fire bed the stage is now set for a" woomph" when oxygen eventually is allowed to be introduced.
BTW: All boilers have different firing cycles relative to the different loads of the dwelling and of the seasonal demands. Pretty hard to just have one setting and be good all season.
I know AHS boiler owners would just love to have AHS mfgr tell them their magic setting for their boilers, but they can not
...you will just have to discover those settings on your own by experimenting.