A filter that fits ATMOS Air & Dual Air PIV. The Filter has a Velcro edge which attaches to the Envirovent unit G4 Grade filtration. It is advised that filters are changed every 4-5 years. If your unit is near a main road or a high pollen area you may need to change them after 2-3 years. Replacement Air Filter suitable for: ATMOS Air Dual Standard ATMOS Air Dual Wireless ATMOS Air Dual App Enabled ATMOS Air Standard ATMOS Air Wireless ATMOS Air App ATMOS Air In-Line These filters are manufactured for us, in the UK, as replacement filters. They are in no way associated with the PIV air system manufacturer. The use of manufacturer names is solely for the purposes of identifying the correct filters