Filter kit (pair) to suit their MRXBOX95-LOFT / LH1 whole house heat recovery unit. 194mm x 396mm x 45mm Nuaire MRXBOX95-LOFT MVHR filters should be replaced every 4-5 years to ensure optimal effectiveness. Clean filters increase the energy efficiency and operational effectiveness of your MVHR unit. The recommended replacement interval is just a guide and filters should be inspected every year to ensure they are still in good condition and are not overly soiled.