Document Kd6mM7dkR4bgeZk5GKXdvnq6

American Society of Heating and Ventilating Engineers Guide, 1934 and the blowers for air supply being mounted in sets adjacent to the boilers. In such cases, one pump set can serve several burner units, and common prudence dictates the installation of spare or reserve pump sets. Pre-heaters and other essential auxiliary equipment also should be in stalled in duplicate. Boiler Settings As the volume of space available for combustion is the determining factor in oil consumption, it is general practice to remove grates and extend the combustion chamber downward to include or even exceed the ash-pit volume; in new installations the boiler should be raised to make added volume available. Approximately 1 cu ft of combustioij volume should be provided for every developed boiler horsepower, and in this volume from 1.5 to 2 lb of oil can properly be combusted. This corre sponds to a maximum liberation of about 38,000 Btu per cubic foot per hour. There are indications that at times much higher fuel rates-may be satisfactory. This in turn suggests that the value of 38,000 Btu per cubic foot per hour should be used with reasonable judgment. For best results, care should be taken to keep the gas velocity below 40 ft per second. Where checkerwork of brick is used to provide secondary air, good practice calls for about 1 sq in. of opening for each pound of oil fired per hour. Such checkerwork is best adapted to flat flames, or to conical flames that can be spread over the floor of the combustion chamber. The proper bricking of a large or even medium sized boiler for oil firing is important and frequently it is advisable to. consult an authority on this subject. The essential in combustion chamber design is to provide against flame im pingement upon either metallic or. fire-brick surfaces. Manufacturers of oil burners usually have available detailed plans for adapting their burners to various types of boilers, and such information should be utilized. CAS-FIRED APPLIANCES The increased use of gas for house heating purposes has resulted in the production of such a large number of different types of gas-heating systems and appliances that today there is probably a greater variety of them than there is for any other kind of fuel. Gas-fired heating systems may be classified as follows: I. Gas-Designed Heating Systems. . A. Central Heating Plants. 1. Steam,.hot water, and vapor boilers. 2. Warm air furnaces. B. Unit Heating Systems. 1. Warm air floor furnaces. 2. Industrial unit heaters. 3. Space heaters. 4. Garage heaters. II. Conversion Heating Systems. '"A; Central Heating Plants. ... l; : I. Steam, hot water and vapor boilers. ; 2. Warm air basement furnaces. 390 Chapter 28--Automatic Fuel Burning Equipment The majority of these systems are supplied with either automatic or manual control. Central heating plants, for example, whether gas designed or conversion systems, may be equipped with room temperature control, push button control, or manual control. Although no exact rules can be prescribed as to the field best covered by each of the foregoing systems, each installation will have problems point ing more or less directly to some particular type of heating equipment. Gas-Fired Boilers Information on gas-fired boilers will be found in Chapter 25. Either snap action or throttling control is available for gas boiler opera tion. This is especially advantageous in straight steam systems because steam pressures can be maintained at desired points, while at the same time complete cut-off of gas is possible when the thermostat calls for it. Warm Air Furnaces There are two general classes of gas-fired warm air furnaces, the gravity furnace which depends upon the natural tendency of heated air to rise, providing the proper circulation of heated air into the room, and the mechanical circulation furnace by which the air to be heated is forced through or drawn through the furnace by means of a fan. Warm air furnaces are variously constructed of cast iron, sheet metal and combinations of the two materials. If sheet metal is used, it must be of such a character that it will have the maximum resistance to the cor rosive effect of the products of combustion. With some varieties of manufactured gases, this effect is quite pronounced. Warm air furnaces are. obtainable in sizes from those sufficient to heat the largest residence down to sizes applicable to a single room. The practice of installing a number of separate furnaces to heat individual rooms is peculiar to mild climates, such as that of southern California. Small furnaces, frequently controlled by electrical valves actuated by push-buttons in the room above, are often installed to heat rooms where heat may be desired for an hour or so each day. These furnaces are used also for heating groups of rooms in larger residences. In a system of this type each furnace should supply a group of rooms in which the heating requirements for each room in the group are. similar as far as the period of heating and temperature to be maintained are concerned. Bedrooms, living rooms, and dining rooms, often present excellent possibilities for this type of furnace. The same fundamental principle of design that is followed in the con struction of boilers, that is, breaking the hot gas up into fine streams so that all particles are brought as close as possible to the heating surface, is equally applicable to the design of warm air furnaces. The desirability of using an appliance designed for gas, when gas is to be the fuel, applies even more strongly to furnaces than to boilers. Codes for proportioning warm air heating plants, such as that formu lated by the National Warm Air Heating Association (see note p. 329), are equally applicable to gas furnaces and coal furnaces. Recirculation should always be practiced with gas-fired warm air furnaces. It not Only aids in heating, but is essential to economy. Where fans are used' in connection with warm air furnaces for residence heating, it is well to 391