Firing can best be done when combustion is good, as but little dense smoke then is given off. Dark spots in the fire, abundance of smoke, unsteady steam pressure, unsteady water line, dirty tubes, and coal in the ash heap are all evidences of careless firing, and should not be tolerated. Experience is the only guide to the best methods of handling the different kinds of fuel under the different conditions to be met with in practice.

The coal should be put in lightly at regular intervals in order to fire the green coal in the front of the furnace and to allow the smoke to pass over a bed of incandescent fuel at the back, and be consumed. Later the coal in front may be pushed back and new coal added to take its place.

Side-firing, i.e., keeping one side of the fire always brilliant while firing green coal on the opposite side, works very well. No established rule, however, can be set for every condition, and much must be left to the judgment of the fireman in each individual case. When firing or cleaning fires where the chimney draught is very strong, it is advisable to check the stack damper to prevent too great a quantity of cold air entering the furnace and causing undue contraction of the plates. In boilers having a large furnace, it is well when cleaning fires to clean one side at a time.

The feed water should be kept constantly on, and the water line maintained at the proper level all the time. Every day the steam pressure should be raised to the blowing-off point, so that the fireman may know that the safety valve is in working order. If at any time, from any cause, the gauge should show the pressure increasing rapidly up to or past the limit, the feed should at once be put on and the draught checked.