Thus, fifteen pounds pressure means a different temperature from ten pounds pressure. Be sure to adjust the weight for the temperature desired. Pushing the weight toward the valve lessens the amount of pressure needed to open the valve. There is usually a steam gage on boilers to indicate the temperature and pounds of pressure inside. When the indicator reaches the point desired, the safety valve may be set so that all steam in excess of the desired amount will escape. When this is done, the temperature will be held constant in the boiler so long as a good fire under it is maintained. CHAPTER X FIREPLACES AND HEATING STOVES =73. Construction of Fireplace.= Fireplaces are an enlargement in the base of a chimney where fire is built. The upper part of the fireplace is sloped forward, and, in some cases, a damper is placed in the chimney to regulate the flow of air upward. The damper should not be so constructed that it will close entirely, for if it did, the smoke would come into the room. The fire in the fireplace burns best when the fuel is put in a grate or on andirons so that air can get under it and be drawn thru it by the draft of the chimney. A steady draft makes the combustion of the fuel complete and thus prevents smoking. The hearth is made of fireproof material and should be wide enough to catch all sparks flying from the fire. A screen is often needed for safety from fire. Do not pile reserved fuel or put rugs on the hearth. Fireplaces and chimneys should be built of fireproof brick, stone or concrete. Have them examined once a year for cracks, as these make them unsafe. The walls of the chimney and the fireplace should be thick enough to prevent danger from fire. =74. Management of Fireplace.= The management of a fireplace is very simple. The draft up the chimney should be properly regulated so that the fire does not smoke. Sparks and bits of fuel should not be drawn up the chimney. The fire should be built so that it is not smothered. Air should circulate thru the fuel. Keep the ashes cleared away. There are some fireplaces which are intended to heat rooms after the manner of hot-air furnaces. The heat and smoke from the fire pass upward thru a metal heater, encased by an air chamber. Much of the heat passes thru the metal, warming the air in the chamber. This warmed air passes thru pipes and registers into the rooms, while the smoke finds its way to the chimney. To complete the circulation of air, the cold air from the floor passes into the air chamber near the floor at the sides of the fireplace. Sometimes fresh air from the outside of the building is mixed with the air in the chamber. If there is an opening in the floor of the fireplace, a damper should be put in this opening to regulate the flow of air. The heater in a fireplace must be kept free from soot and ashes. If the metal is covered with soot, heat will not readily pass thru it, and the soot will collect moisture and cause rusting.