This type of system will often appear in more modern, well-insulation dwellings, particularly apartments, or on occasions, social housing where inadequate ventilation has been identified. The key to this system is that it covers the whole-house – individual extractor fans in a bathroom or kitchen do not fall under this.

Mechanical Extract-Only Systems

Extract-only systems are fan-driven ventilation systems which only extract and dispel air from the dwelling.

These types of system can either be centralised or decentralised.

With a centralised system, all the air is ducted and expelled by means of a central fan. Decentralised systems use a number of continuously-running fans around the dwelling.

Balanced whole-house ventilation systems

Balanced ventilation provides fresh air to habitable rooms within the dwelling, as well as extracting exhaust air from wet room.

In newer systems, it is common for these balanced systems to be coupled with some for of heat recovery system, however only full SAP EPCs are able to model this heat recovery effectively.

Positive Input Ventilation Systems

A PIV system is another fan-driven system which often provides ventilation to the dwelling from within the loft space.

Where a PIV system is draughted from within the loft itself, it should be considered as ‘natural ventilation’, however, if the PIV is supplied directly from the outside, it would be considered as ‘mechanical ventilation - extract only’.