Abstract: A heat recovery apparatus for increasing the efficiency of a furnace having a cold air return, a burner, a hot air outlet, and a hot air exhaust. The heat recovery apparatus comprising a finned coiled heat exchanger located in the exhaust and having a water inlet and a water outlet. The water outlet connected via a silicone tube to a second water inlet on a core heat exchanger located in the cold air return. The core heat exchanger having a water outlet connected via second silicone tube to a water reservoir tank. The water reservoir tank containing water and a pump submerged within the water. The pump having a third water inlet and a third water outlet. The third water outlet being connected via a third silicone tube to the water inlet of the coiled heat exchanger. The heat recovery apparatus increasing the efficiency of a non-high efficiency furnace.