A Standard Filter

• 1). Locate the filter slot on the side of your furnace. The filter slot typically has been cut out of the cold air return duct attached to the side of the furnace.
  
  
• 2). Pull the old filter out of the slot.
  
  
• 3). Examine the filter to see if the size is displayed anywhere. If you cannot find the size, measure the height and width of the filter slot with a tape measure.
  
  
• 4). Insert the new filter into the filter slot.
  
  

HEPA Filter

• 1). Open the filter cover using a screwdriver to remove the screws securing the housing. The housing is a square-box shape that has been placed between the furnace and the cold air return duct.
  
  
• 2). Pull off the cover and pull the old filter out.
  
  
• 3). Insert the new filter and set the cover back in place. Replace the screws and tighten them with the screwdriver.