Simply put MVHR is a system where warm moist air is extracted from the bathrooms and kitchens of a property, ducted through to a heat exchanger which then transfers the heat to the incoming fresh air which is then ducted back out to your other living spaces within the property.

The moist air that was extracted from the bathrooms and kitchens is then expelled to the outside air and the fresh air that was brought in to replace the expelled air is heated via heat exchanger by the outgoing stale moist air. Most of the MVHR units out there claim to be >90% efficient, this in reality means that virtually all heat that is extracted from the warm moist rooms is taken out and distributed as warm fresh air across other areas of the house. Its a known as a balanced system, meaning that the volume of air extracted is balanced by the incoming fresh air.