HEPA Filter Sales carries high efficiency disposable MERV 11 replacement air filters manufactured by Powerguard for WaterFurnace. They are considered by WaterFurnace to be the OEM replacement pre-filters for all their Geothermal Comfort Systems. Replacement air filters from WaterFurnace are sized right for a proper fit and they are designed to get the maximum performance from your system. If you do not see the size of filter you need, please contact us and request a quote for your filter type and size.