Passive heat recovery or defrosting device using a closed loop heat transfer circuit

A passive heat recovery or defrosting apparatus features an evaporator, a condenser, and vapour and liquid conveyance lines connected therebetween. The vapour and liquid conveyance lines respectively connect to upper and lower ends of the evaporator and condenser. The evaporator and/or condenser has a ring-shaped body for fitting around or inline with a pipe to achieve heat exchange relation with a fluid passing therethrough. The evaporator is installed on or inside a warm pipe or duct (e.g. waste drain pipe, clothes dryer exhaust duct, flue pipe, or indoor section of a sewer vent stack) at a lower elevation than the condenser. The condenser is placed on an outdoor end of either a sewer stack or air intake duct for defrosting purposes, or is placed on a water supply line or air intake of a hot water tank, clothes dryer, etc. Working fluid circulates passively between the evaporator and condenser.