How to Determine Correct Furnace Filter Direction

Posted by: Mas Broto
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Where the arrow of the air filter should point towards when replacing furnace filter? The arrow should always point in the direction the air is flowing. But sometimes, you may not know which way the air is flowing. Here’s an easy way to figure out which way the air flow arrow goes and determine the correct furnace filter direction.

Furnace filter that’s installed in the wrong direction will cause inefficiency. The air will have to pass through the filter through the less porous side. This will make it more difficult for your air handler to keep air flowing through the filter, which will force your furnace to work harder and use more energy. This could lead to higher utility bills and possibly damage your furnace.

Furthermore, installing your filter backwards, it will not be as effective at trapping particles from your home’s air. You will have a decrease indoor air quality.

So be sure to look for the arrows that are printed on the sides of the air filters, because they show you which direction the furnace filters are supposed to be.

Arrow which way does air filter go in furnace? The arrow must always face toward the furnace and away from the return duct. Although the two sides of air filter might look the same, they are not. You’d find that one side filter is more porous than the other.

The right furnace filter direction allows the filter to effectively trap airborne particles while also reducing the slowdown of air flow through your furnace system.

How Often You Should Change Your Air Filter?

Furnace filters should be changed regularly to keep your entire HVAC system running smoothly and to maintain best indoor air quality. How regularly you should replace your furnace filters could depend on the following:

  • Type of air filter
  • Pets
  • Allergies
  • Air pollution levels

In general, this is how often changing furnace filters needs to be done:

  • 1″ – 2″ filters, replace them every 1 to 3 months
  • 3″ – 4″ filters, replace them every 6 to 9 months
  • 5′ – 6 filters, replace them every 9 to 12 months

While the above factors affect the frequency of furnace filter replacement, you should visually inspect your filter every month to check for unwanted particle escalation. If the dirty air filter is completely layered with dust and debris, it’s a good idea to replace the air filter even if it hasn’t reached the end of its recommended lifespan.

Which Way Does The Arrow Go On An Air Filter In The Furnace?

The easiest way in determining which way the furnace filter direction is to refer to the old filter before removing it and installing the new one in the same way. If the old filter has already been removed, you can use these tips as a guide when replacing furnace filter.

The arrow must always face toward the furnace and away from the return duct. The pleated part of the air filter should be facing you when you install it and the other side, which usually consists of a metal mesh or cardboard frame should be pointed towards the return.

You can also refer to your unit’s manual for exact filter locations and installation instructions if available.

Changing furnace filters regularly provides great impacts on home comfort and indoor air quality, as well as energy efficiency, and the longevity of your system. Considering how important a furnace filter direction, it is a good idea to ask your HVAC technician to explain the best filter, when to change and how to install.

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Mas Broto
Have been in the heating and air conditioning (HVAC) industry for over 20 years. He is person that will grow and thrive to learn more about the HVAC industry throughout his career. Mas Broto is also a blogger, who's dedicated to bringing you the best knowledge to get ahead in the game of life.

2 thoughts on “How to Determine Correct Furnace Filter Direction”

  1. I am still not sure which way to insert the filter. I’m not sure what the return duct is or what it looks like. My filter is inserted horizontally. The air from my central air conditioner blows upwards through my furnace, so should I be inserting the filter so the arrow is pointing in the same direction (up) or the opposite direction that the air is blowing (down)?

    • The arrows indicate that air is being pulled INTO the system, so make sure the arrows point INTO the system.

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