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The science
The average English house has so many cracks and holes in it that it equates to leaving a 2ft by 2ft window open all year round. This inefficiency can be tackled by insulating and draught-proofing your house.  Once your house is insulated and draught-proofed, the most efficient way to heat it is with an MVHR unit. 

The system requires around half an air change per hour, meaning all the air in your home is replaced roughly every two hours. It works by drawing air from warm areas of your house (eg kitchen and bathroom), extracting the heat out of this air, and then passing it into the fresh air drawn in from outside.

A highly efficient counter-flow heat exchanger can recover up to 94% of the heat that would otherwise be lost.

Application
MVHR is best installed when renovating your property, in conjunction with insulation and draught-proofing.

Certain elements need to be borne in mind when designing and installing an MVHR system:

• how the ductwork runs throughout the property, including how to minimise the visual impact of outlet ducts and boxing
• how to ensure the air entering the MVHR is at the best possible temperature. One way to do this is with an underground heat exchanger, which cools the air in summer and warms it in winter.
• will the ductwork carry noise from the MVHR or other rooms connected to the system? Although this is often not a problem, it can be eliminated entirely by the inclusion of mufflers and sound attenuation devices.
• filters need to be changed at least once per year, and sometimes twice depending on the system and its usage.