Document Znye9LZ9ox2O5bxjOJ7L67BLJ

1 American Society of Heating and Ventilating Engineers Guide, 1935 oversize and favored in every way. This precaution is particularly important when long ducts and short ducts are used in the same system Chapter 24--Gravity Warm Air Furnace Systems. friction and turbulence, and that they be located to prevent preheating of the air before it reaches the furnace. <n V) D < Id X & The long ducts must be oversize, if they are to operate satisfactorily in parallel with short ducts. Return ducts from upstairs rooms may be necessary in apartments or other spaces closed off or badly exposed. Metal linings are advisable in such ducts. It is important that these ducts be free from unnecessary 394 . Return Connection to Furnace Circulation is accelerated if the drop to the furnace is through a round inclined pipe with, say, two 45-deg elbows rather than through a vertical -' "drop and two 90-deg elbows. The top of the shoe should never enter 395