Document M41N87aQrD6ynKV19O6Y6Rk7a

American Society of Heating and Ventilating Engineers Guide, 1934 Chapter 24--Gravity Warm Air Systems 7. Size of furnace necessary to supply the warm air required to overcome the heat loss from the building. This she should include square inches of leader pipe area which furnace must supply. It is also desirable to call for a minimum bottom fire-pot diameter in inches, which is the nominal grate diameter. 8. Area and dimensions.in inches of chimney and smoke pipe. If an unlined chimney is to be used, that fact should be made .clear. The heat loss calculations should be made in accordance with the procedure outlined in Chapter 7, taking into consideration the trans mission losses as well as the infiltration losses. SIZES OF LEADER PIPES In a gravity circulating warm-air furnace system the size of the leader to a given room depends upon the temperature of the warm air entering the room at the register. A reasonable air temperature at the registers must, therefore, be chosen before the system can be designed. The National Warm Air Heating Association has approved an air temperature of 175 F at the registers as satisfactory for design purposes. At this tem perature, the heat-carrying capacity (heat available above 70 F) per square inch of leader pipe per hour for first, second or third floors is shown by Fig. 1 at 175 F to be 105, 170 and 208 Btu respectively. For average calculations, the values 111, 166 and 200 will simplify the work and may be satisfactorily substituted for these heat-carrying capacities. If H represents the total heat to be supplied any room, the resulting equations \are:Leader areas for first floor, sqqare inches = H = approximately 0.009// (1) \ Leader areas for second floor, square inches = ^H = approximately 0.006/7 (2) Leader areas for third floor, square inches = ^ - approximately 0.005/7 (3) In designing for a lower warm-air register temperature, say 160 F, the factors 111, 166 and 200 become 80, 140 and 166 (Fig. 1 at 160 F), and the resulting equations are: Leader areas for first floor, square inches = = approximately 0.012// (4) Leader areas for second floor, square inches = H = approximately 0.007H (5) Leader areas for third floor, square inches = H -- approximately 0.006// (6) , These equations are applicable to straight leaders from 6 to 8 ft in length. . Longer leaders must be very thoroughly covered or else the vertical stacks must be increased in area as discussed under wall stacks. If some provision is not made for these longer leaders, the air tempera ture may be much lower than anticipated and the room will not be properly heated. - --- . While Fig. 1 takes care of the drop in temperature in straight leaders up to 8 ft in length connected to stacks having about 75 per cent the 319