Abstract: A flue gas heat recovery apparatus for reconstituting thermal energy normally lost through the venting of flue gases from a heat liberating plant is disclosed. The apparatus can be employed with forced air or hydronic systems and includes a compressor which draws hot gases from the exhaust flue through a first heat exchanger located in a cold fluid return to the plant, thereby transferring thermal energy from the gases to fluid (typically air or water) flowing in the return duct. The compressor operates to substantially elevate the pressure and temperature of the flue gases passing therethrough and discharges them through a second heat exchanger located in the return duct upstream of the first heat exchanger to further transfer thermal energy from the gases to the fluid flowing therein. Gases exiting the second heat exchanger are directly vented to the atmosphere or, alternatively, are first filtered to remove particulate matter.