Occasionally found in duct systems that use joist spaces or other parts of
the building structure to channel air flow, blind-alley ducts occur as
a result of mistakes made during installation. A blind-alley duct leads
nowhere (except possibly to the outside) while the register it was supposed
to serve has no source of heat. The room containing this register is
therefore cold. If a room always seems too cold or a register doesn't seem to
have any air flowing out of it, it may be worth investigating.
