The fuel for a coal-fired furnace or boiler may be fed either automatically or by hand. Both methods have certain advantages and disadvantages. For example, automatic (stoker) firing is initially more expensive because it requires the purchase and installation of a suitable mechanical stoker to feed the coal to the furnace or boiler. As a result, stoker firing is a common practice in larger buildings (e.g., stores, hotels) where the initial high cost of the equipment can be more easily absorbed into the total cost of the structure. Despite the relative high cost of stokers, there are some designed for use in single-family residences.
Because there is no need to invest in special and expensive coalhandling equipment, hand-firing the coal has been the traditional method used for firing house heating furnaces and boilers. Although hand-firing coal is less expensive than stoker-firing for these smaller installations, the following objections to the handfiring method should be noted:
• The frequent opening of the furnace or boiler doors allows a large excess of air to enter and chill the flame. The combustion efficiency of the flame therefore tends to fluctuate.
• The dumping of a lot of fuel at each firing results in a smoke period until normal combustion conditions are restored.
• Hand-firing coal is by its nature an intermittent firing method. The flame often reaches a low and inefficient level or is extinguished before new fuel is added.
