How often you need to change the filter on your Ruud air handler really depends on the environment in which it's operated. Ruud recommends changing the filter every two months. If you live in a dusty area or have long-haired pets, consider changing the filter once a month. The filter is inside of the air handler housing, by the return air duct. You can purchase replacement filters at home improvement centers. If you are not sure what size to purchase, open the filter door and look at the edge of the current filter. The size of the filter is stamped on the filter edge.
Turn off the circuit breaker to the Ruud air handler. The circuit breaker is located in your home's electrical panel box.
Go to the air handler and locate the filter housing. The filter housing will be between the return air duct and the air handler. There will be either two thumb screws or two screws that have small ring handles on them.
Turn the screws counter-clockwise with your fingers and open the filter housing door. The door is only slightly wider than the thickness of the filter. Pull the dirty filter out of the air handler.
Place the new filter into the housing and close the filter housing door. Turn the securing screws clockwise to lock the door. Turn on the circuit breaker to the unit.