Single room heat recovery units are also referred to as wall heat recovery units, ductless
HRUs, push-pull units, etc. This type of heat recovery unit is recommended when
the traditional mechanical ventilation system with heat recovery cannot be installed,
e.g. when there's no space for the network of ductwork.
Wall heat recovery units are often mounted in an existing, older building, especially for retrofitting, refurbishment applications. Room heat recovery units are recommeded when the issue of poor air quality arises due to not working gravity ventillation system. Poorly working natural ventilation system often leads to high indoor humidity and the risk of mould growith.
In comparison to wholehouse ventilation system, where the unit is installed in utility room like a laundry room, single room heat recovery units as the name suggests must be
installed in every room separately. It's recommended that the units are installed in pairs, so the one unit supplies fresh air, while the other one removes extracted air.