An air cleaner is provided according to an embodiment of the invention. The air cleaner includes an air duct including an inlet end and an outlet end, a pre-filter positioned at the inlet end, an electrostatic precipitator positioned in the air duct downstream of the pre-filter, a post-filter positioned in the air duct downstream of the electrostatic precipitator, and a fan unit positioned in the air duct downstream of the post-filter. Airflow travels from the inlet end to the outlet end. The airflow first encounters the pre-filter, encounters the electrostatic precipitator after encountering the pre-filter, encounters the post-filter after encountering the electrostatic precipitator, and encounters the fan unit after encountering the post-filter. Each of the pre-filter, the electrostatic precipitator, and the post-filter can be separately installed and removed from the air duct.