Document dqrJ7Z3aqzgZ7LY7XN56a51R

American Society of Heating and Ventilating Engineers Guide, 1936 Chapter 24--Gravity Warm Air Furnace Systems 7. Size of furnace necessary to supply the warm air required to overcomethe heat loss from the building. This size should include square inches of leader pipe area which the 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 and Air Conditioning Association has ap proved an air temperature of 175 F at the registers as satisfactory for design purposes. At this temperature, 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, square inches = jj-j = approximately 0.00977 (1) Leader areas for second floor, square inches = H = approximately 0.006# (2) . lob * Leader areas for third floor, square inches = H zuu = approximately 0.00577 (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: "' H Leader areas for first floor, square inches = -rjr = approximately 0.01277 OU (4) Leader areas for second floor, square inches = = approximately 0.00777 (5) Leader areas for third floor, square inches = H = approximately 0.00677 (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 of the 419