How to Change the Filter in an Older Furnace

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Keeping your furnace filter clean is an important aspect of home maintenance, especially if the furnace is older. Over time, dust and other debris can collect in the filter, reducing the efficiency of the furnace. Replacing the filter will allow the air to heat more quickly, thereby saving on energy usage and costs. How often a filter should be changed depends on the conditions in which it is used, but a general rule of thumb is to change the filter once every 6 months.


Step 1

Locate the main circuit breaker to the furnace and switch the power to "off."

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Step 2

Open the door on the service panel and locate the filter. The filter is usually found near the blower compartment. In especially older models, the filter may be found located directly inside of the access door or in the grill. If you are unable to locate the filter in your furnace, contact a qualified furnace technician.

Step 3

Pull out the mesh filter and discard.

Step 4

Slide the new filter into the space where the old filter had previously been. Be sure the arrow located on the plastic or metal edge of the filter is pointed inward toward the furnace.


To reduce indoor allergens, consider an allergenic reduction filter. When the furnace is used constantly during winter months, you can replace the filter up to once per month. The blower motor of an old furnace should be lubricated each year. Lift the rubber caps around the oil ports and place a few drops of oil into the opening.

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