Which Way Should My Furnace Filter Face?
By Melanie Dawn
November 25, 2024
It’s easy to forget about your furnace filter, but it’s an important part of HVAC maintenance. Replacing your filter regularly can help prevent breakdowns and keep your system running efficiently.
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OK, so you decide to tackle this (admittedly simple) home maintenance task. Standing in front of your furnace, you find yourself questioning which direction the new furnace filter is supposed to go into the filter slot. Uh oh. What to do now?
Is There a Wrong Way to Put a Furnace Filter In?
You may not think it matters, but there are right and wrong ways when installing a furnace filter. Installing the filter incorrectly can restrict airflow on a furnace, costing you money on your energy bill. Regardless of what type of filter you use, it's made to allow air to flow one way. When the filter faces the correct way, you’ll have cleaner indoor air and maximum airflow.
What Happens if I Put the Furnace Filter in Backward?
A furnace filter is designed to go in the furnace one way. If you accidentally put it in the wrong way, a few things can happen.
Reduced airflow. Air filters have a reinforced side that’s meant to face away from the blower. If you put the filter in backward, it restricts the flow of air. Your system will perform poorly, and you may feel less air blowing through the vents. In some cases, if the air filter goes in incorrectly, it will fall apart quickly due to the air pressure as it moves through the system.
Dust buildup. Filters trap dust and debris before it enters your unit. When the filter is backward, it can’t trap these particles effectively, which could lead to a buildup inside your components and ductwork.
Increased energy bills. With restricted airflow, your furnace must work harder, making it consume more energy. Over time, this can result in higher electric bills.
Reduced lifespan. With added strain on your furnace, parts will wear out faster. This can lead to expensive repairs and reduce the lifespan of the system.
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Which Direction Should My Furnace Filter Go?
Most filters have an arrow along the edge indicating the correct airflow direction. Air flows from the return duct through the filter and into the furnace. The arrow on the filter should face toward the filter and away from the return duct. Simply slide the filter inside the slot with the arrow facing the inside.
What if There Isn't an Arrow on the Air Filter?
If your filter doesn’t have an arrow, figuring out the correct installation direction can be tricky. Start by examining the filter. One side should have a wire mesh or added support. The other side will appear softer and more porous. The reinforced side should always face the furnace because it’s built to withstand the system's air pressure. If you’re still in doubt, you can always check the owner’s manual or the manufacturer’s website for specific installation instructions.
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