The heater should receive regular attention, and if the demands for heat are intelligently anticipated, as they ordinarily can be, the house can be warmed with minimum trouble and fuel. When the rooms become too warm, the fire should be checked by stopping the admission of air under the grate and decreasing the draft by opening the " check damper." If, as often is done, the ash-pit damper or the ash-pit door be allowed to remain open, and the draft reduced by opening the fire door, the combustion of the fuel continues, although at a slower rate, but the cold air entering the fire door chills the heater so that little heat is realized from the coal.

Sometimes the draft is so strong that the difficulty of controlling the fire is increased, especially when the demand for heat is small or the fire is to be banked. To facilitate control under such conditions, it is usually advisable to have, besides the check damper, a plain damper in the smoke pipe. This damper should fit the smoke pipe loosely and must never be entirely closed; during most of the heating season it can be kept partly closed, but during severe weather, when more heat is required, it can be opened wide. Sometimes the draft may be insufficient to burn the necessary quantity of the particular fuel used. If such a condition is always noticed in severe weather, the heater may be too small, the smoke pipe may be choked or be poorly fitted to the heater or to the chimney, or the chimney may be too small or be obstructed by soot or debris.

If the draft trouble proves to be due to leaky connections or to obstructions, it can readily be corrected. If the heater or the chimney is too small, the difficulties may be lessened either by firing more frequently and keeping the fuel-bed thinner, or by using larger coal, or fairly uniform size, in order that the air may more easily flow through the fuel-bed. Conversely if the draft is very strong, a smaller size of coal may possibly be used to good advantage. Under no circumstances should the top of the chimney be lower than the highest part of the roof, or a current of air may be forced down the chimney and the basement be filled with smoke when the wind blows in certain directions. Similar trouble may be experienced if the chimney is not as high as an adjoining building.

If the bottom of the ash pit is on a level with the floor, or only a short distance below the grates, as is ordinarily the case, ashes cannot be allowed to accumulate under the grates for more than two days, or possibly more than one day, except in moderate weather.

Brightly tinned hot-air furnace pipes often lose less heat when bare than they do when covered with one or two layers of asbestos paper, since the latter radiates heat so much more readily than the bright tin as more than to balance the insulating effect of the thin asbestos covering. Of course if the pipes were originally black, the covering would be useful, and if the insulating material were thick enough (3/8 inch or more) it would save heat even on bright tin pipes.*