A hot air furnace heats and distributes air through its ducting
system.The ducts are usually made of sheet metal and are most obvious in
your basement, where they hang from the floor joists.The return, or
cold air, ducts bring air to the furnace, usually collecting it
centrally in the house. The return air trunk duct is the big rectangular
duct along the basement ceiling that enters the bottom of the furnace.
The supply, or warm air, ducting usually exits from the top of the
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