When choosing a heat recovery ventilation system for your house, it is important to consider the amount of heat you would like to recover and the money you would like to save. Large amounts of heat (up to 90%) can be recovered with an MVHR system that would normally be wasted using traditional ventilation systems such as extractor fans and trickle vents. All this for less than £30 a year in energy costs (in an average 4 bedroom house).