The GasSaver has successfully been used in a number of developments, to count towards achieving Code Levels 3 & 4 of the Code For Sustainable Homes.
To maximise the contribution of the GasSaver to a particular dwelling, where possible, consideration should be given to adjusting building fabric properties such as wall U-values and air permeability. Generally speaking, reducing these values gives a better percentage saving for a given dwelling.
In some scenarios it may not be possible to achieve Code Level 3 without additional energy saving measures. In such cases, consider the use of other low cost methods to improve the DER such as mechanical ventilation with heat recovery.