How do I know what size my filter is?

MG2R furnaces designed for top return are shipped with a non-reusable single 18”x18”x1”air filter from the factory. Accessing the filter does not require a tool and can be easily removed from inside the blower compartment. The filter is secured with a U-shaped retaining bracket. It is recommended that the filter be cleaned or replaced monthly. Newly built or recently renovated homes may require more frequent changing until the construction dust has minimized. You can reference the Installation Manual on the product page in the Specifications Section. Thank you for visiting HVAC-Direct. If you need additional information, please feel free to call us!