This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
In some cases it is desirable to return air to the furnace from the rooms above, to be reheated. Ducts for this purpose are common in places where the winter temperature is frequently below zero. Return ducts when used, should be in addition to the regular cold-air box. Fig. 31 shows a common method of making the connection between the two. By proper adjustment of the swinging damper the air can be taken either from out of doors or through the register from the room above. The return register is often placed in the hallway of a house so that it will take the cold air which rushes in when the door is opened and also that which may leak in around it while closed. Check valves or flaps of light gossamer or woolen cloth should be placed between the cold-air box and the registers to prevent back drafts during winds.
The return duct should not be used too freely at the expense of outdoor air, and its use is not recommended except during the night when air is admitted to the sleeping rooms through open windows.