3M offers a line of air-handler filters called Filtrete. These filters come in a variety of sizes based on the size of your unit and how much air is intended to pass through at a specific time. A 20x25x1 filter is actually 20 inches high by 25 inches wide and 1 inch thick. The filters are used to filter the air as it passes through the home's central air-handler unit, which is a device used to condition and circulate air as part of a heating, ventilating and air-conditioning system, also known as an HVAC system. Replace the air filter periodically to ensure efficient airflow. Dirty filters reduce the airflow that warms and cools your house, and add extra wear and tear to the system. The filter also helps improve air quality in your home by trapping allergens and pollen.
Ensure the power is disconnected to the air-handler unit by turning the circuit breaker controlling the unit to "Off."
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Locate the filter cover and housing; look along the return air duct for a small space labeled "filter." Notice the screws holding the cover to the filter housing in place. Use a screwdriver to remove the screws. This will give access to the filter. If your unit's filter housing does not have screws, look for clips to unhook or simply slide the cover out to gain access to the 3M filter.
Install the 3M 20x25x1 replacement air filter by sliding it into place in the direction of the arrows printed on the filter. Failure to insert the filter with the arrows pointing in the direction the air flows will result in inadequate airflow and filtration.
Reinstall the filter housing cover and replace the two screws. Tighten and secure the two screws in place with the screwdriver. Restore power to the air-handler unit by turning the circuit breaker to "On." Discard the dirty filter. Repeat this process anytime the 3M filter needs to be changed.
Replace your air filter every three to six months. Appearance doesn't accurately indicate whether your filter is "dirty."