The Environment:

Ashes from burning coal:
If the ashes are from burning coal, then you must be more aware of proper ash removal for
many reasons. First, you will have much more ash to remove versus wood. Second, coal ash
is not beneficial to a garden because its potassium and phosphorus content are very low
compared to wood. Third, coal ash also contains a great deal of other elements, such as cobalt,
boron, and arsenic among others, which are toxic to plants, animals, and people. You must be careful when burning coal because ash can trap unburned carbon which means that more
unburned fuel is tossed away with coal ash versus wood. What else can you do with the ashes once removed from the appliance? In more rural areas, people will place them on their driveway
to help overcome a slick surface during winter. With coal ashes, you may do the same, but coal
ashes can affect springtime vegetation as it washes away during the late winter. After a period
of time when you feel that there are no longer any potentially "live" coals, you should bag and dispose of coal ashes at a transfer station or the local landfill.

Ken Rajesky, Hearthlink International

Coal Ash Note:
you will get approximately 18 gallons of ash / ton of coal that you burn.

Smoke:

Smoke is essentially water vapor and unburned fuel, caused by an incomplete burn and the quality of the fuel supply. In order for the fuel to burn completely, the right environment must exist. This includes the proper mix of fuel, oxygen and heat, which is what theseforced draft outdoor hot water furnaces are designed to do when they are burning!

Hence why you will create smoke when an appliance is "throttled down" or idles (if it is
automatic controlled and has no demand or manually choked down). This is why you should
load your appliance more often with less fuel, as a smaller fire is a hotter fire that will burn more efficiently with less ash and smoke. If your appliance has a glass door you should always be
able to see the fire through it! It should never creosote up to the point that you cannot see the
fire, if the glass creosotes up think about what the inside of your chimney looks like.