Any conservation system whereby some space heating or water heating is done by actively capturing byproduct heat that would otherwise be ejected into the environment. In commercial buildings, source [..]

Waste heat recovery means recovering heat discharged as a byproduct of one process to provide heat needed by a second process. It is the process of recovering heat from hot streams with potential high [..]

Converting wasted heat into useable electric power. 

The recovery of heat from the exhaust system of boilers, gas turbines, and other similar devices.

A process for making use of available heat that would otherwise be wasted or lost to the atmosphere. Heat including steam is produced at various stages of natural gas production, processing and transmission and can be recovered in some situations.