Where is the filter for a Concord 80Plus Furnace

If you are filtering your return air at the return air grill inside your home you may not have a filter inside the furnace. But if you did have one it would be in the blower compartment side of your furnace. Many installers will remove that filter after construction or installation if it is being filtered inside. Reason being most home owners will for get or just won't replace the filters inside the furnace.