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When and How to Change an Air Filter

HVAC November 21st, 2021 Back to HVAC Blog
how and when to change an air filter

There are always small maintenance tasks that homeowners can do themselves – helping save money while also avoiding unnecessary repairs. One of these is a simple task that we recommend taking care of every 1-3 months: changing your home’s HVAC system air filter.

What is an air filter?

Air filters in furnace or heat pump HVAC systems serve to screen out large airborne particles that can clog the system.

These filters are disposable and biodegradable and can be purchased at any hardware store. They are usually available in multi-packs, but before you make the investment know that air filters are not universal in size. Make sure you buy the correct size for your unit. 

Why should you change your air filter?

This is a simple and inexpensive task that, if ignored, could lead to problems with your system. A dirty filter can lead to poor air quality and your system running inefficiently by reducing or preventing air flow, causing the entire system to work even harder to warm or cool your house (depending on the season). As time goes on without a filter change, it could cause the entire system to fail – meaning a costly repair or replacement.

If your unit is in your basement, there is a possibility that a dirty air filter could be exposed to dampness which can lead to mold growth. As soon as the mold growth is present, there is a chance  that mold could spread throughout your system.

Avoid future headache and harm by changing your air filters monthly or every three months.

How to change the air filter in a furnace:

Before you can replace the air filter in your central air unit, you need to find it. Check the owner’s manual if you are not sure. Once located, check the soon-to-be old filter for size specifications, but do not remove it (especially if your system is still on).

A typical air filter size is 16x20x1. It is important to use the right filter for your unit.

Once you have purchased your air filters, you are ready to begin.

  1. Turn off the unit (from the thermostat) before replacing the filter.
  2. Carefully remove the old filter. Clean up any residual dust.
  3. The air filters have an arrow on the side indicating the direction of airflow. When inserted, the arrow should point toward the furnace.
  4. Make sure there aren’t any gaps around the filter frame. If this is the case, you may have the wrong size filter, or the filter itself may be defective or damaged.
  5. Turn the unit on and observe it while it’s operating to make sure the filter stays in place.
  6. Note the date of filter replacement. You can write the date it was installed on the edge of the filter (with marker). You might even set up a monthly calendar reminder so you don’t forget to check the air filter.
  7. When you check on the air filter one month later, pay attention to any dust or dirt build-up. If the air filter still looks clean, there is no need to replace it at that moment. Check it again in another month.

How to replace the air filter in an air handler cabinet:

  1. Step one is always to turn off the power to the HVAC unit.
  2. Remove or unlatch the door and clean thoroughly.
  3. Check the filter type. If it is disposable, replace with a new filter in the correct size.
  4. If it is a reusable filter, lightly brush it to remove surface dirt, then vacuum with a soft brush attachment over the face.
  5. Next, in the opposite direction of the airflow, run water through the filter.
  6. Make sure the filter to thoroughly dry before you replacing it.
  7. Do not turn the HVAC unit back on until the clean, dry filter is in place.

How to change the air filter in a return air duct:

  1. Unhook the latch on the cover grille.
  2. Wipe the grille clean with a microfiber cloth or use a vacuum with a brush attachment. If needed to get difficult dust between the slats, try wrapping the tip of a flat screwdriver with a microfiber cloth.
  3. Remove the old filter and insert a new one. Filters are one directional, so make sure it is facing the right direction.
  4. Close the cover grille and secure the latch.

How to change the air filter in a window AC unit:

Although every window air conditioning unit will be slightly different, the following general steps should help guide you through the process.

  1. Turn off the AC and unplug the unit.
  2. Remove the front cover; if needed, give it a thorough cleaning.
  3. Remove the air filter, take it outside and shake vigorously to remove as much dust and dirt as possible.
  4. Lightly rinse the filter with soapy water, do not use anything caustic, then rinse with clear water until clean.
  5. Let the filter air-dry thoroughly before attempting to replace it in the AC unit.
  6. Replace the filter by lining up the notches on the filter frame with the spaces inside the filter compartment.
  7. Replace the cover and restore power to the unit.

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