Heat recovery ventilation (HRV) (also known as a heat exchanger, air exchanger or air-to-air exchanger) is a ventilation system that employs a counter-flow of heat between the inlet and outlet airflow. The heat recovery allows efficient renewal of the interior air without wasting the heat of the interior air. This saves heating energy in values ​​between 15 and 30% depending on the quality of the windows and doors regarding their air permeability.

Energy recovery ventilation") (ERV) are closely related, however they also allow the transfer of the humidity level of the exhaust gases from air to intake air.

The energy efficiency of a building is implemented in several ways, among which stand out, due to its weight in the thermal load, the thermal insulation of the building envelope (walls, ceilings, floors and glazing) and the improvement in the tightness of openings through weatherstripping. weakly ventilated.[2]​.

Since all buildings require a source of fresh air, the violation of the rights of workers in office buildings and the general population in housing became evident. This was mainly in the US and Canada at first but then spread to northern Europe until reaching the Mediterranean and Eastern countries. Although opening a window provides ventilation, the building loses sensible and latent heat in winter or summer, reducing energy efficiency and wasting energy that must be compensated by the heating, air conditioning and ventilation systems. Heat recovery technology offers an optimal solution: fresh air, better climate control and adequate energy efficiency.

HRVs and ERVs are devices that can be installed and operated independently, or purpose-built, or attached to existing HVAC systems. For a small building where almost every room has an exterior wall, then the HRV/ERV device may be small for single room ventilation. A larger building will require either many small units, or one large central unit. The only requirements for installing a heat recovery unit are to have access to an exterior wall or that access is through a duct whose section will be related to the volume of air to be renewed and the frequency, and of course an electrical connection for the fan. When a centralized system is used, it must be a "forced air" type due to the large volumes to be renewed.