MVHR provides controlled fresh air for a healthy indoor environment and works by continually extracting warmer air from damp rooms in the house, while drawing fresh air in from outside at the same time. The heat from the air is then recycled though a heat exchanger with a heat recovery unit which is then reused to temper the fresh air supply. By reusing up to 90% of the heat that may otherwise have been lost, a Mechanical Ventilation with Heat Recovery system is the ideal way to ventilate and heat an airtight home.