Which Way Does a Furnace Filter Go In?

One of the most important maintenance tasks every homeowner should perform is regularly changing their HVAC system’s air filter. A clean furnace filter helps your system run more efficiently, keeps your home’s air quality in check, and prevents unnecessary wear and tear on your heating and cooling system. However, if you’re new to HVAC maintenance, you might be wondering, “Which way does the furnace filter go in?”

It may seem like a simple question, but installing your HVAC filter incorrectly can affect the performance of your system and even lead to bigger issues down the road. So, let’s walk through how to identify which way the filter should go, why it’s important, and how it affects your home’s comfort.

How to Tell Which Way an HVAC Filter Should Go In

Most air filters have a specific direction in which they need to be installed, and the good news is that many filters are designed to make this easy for you. Here are the most common ways to figure out the correct installation direction:

1. Look for the Arrows

The easiest way to tell which way the filter should go in is to look for arrows printed on the frame. Most filters have arrows that indicate the direction of airflow. These arrows should point in the direction the air is flowing, which is toward the HVAC unit/air handler and away from the return vent. If you’re unsure, just remember that the air is pulled through the filter, so the arrows should point toward the furnace itself.

2. Observe the Pleats

The pleats on the filter can also help determine the right direction – they should face the airflow, toward the return duct side. The framed side, which contains some cardboard and metal wiring, should face the furnace.

2. Check the Filter’s Label or Writing

If there are no visible arrows, the filter may still have some printed instructions. Many filters have “Air Flow” or “This Side Toward Furnace” written on the frame to guide you. If that’s the case, make sure to position the filter so that the labeled side is facing the furnace and the opposite side is facing the return air vent.

What Happens If You Install the Filter Wrong?

Some issues that can result from installing your air filter the wrong way include:

• Reduced Airflow and Efficiency: Installing the filter backwards restricts airflow, making your furnace work harder to maintain proper circulation, which can increase energy consumption and drive up utility bills.
• Decreased Air Quality: A backwards filter doesn’t trap dust and allergens effectively, causing pollutants to circulate through your home and potentially lowering indoor air quality.
• Increased Strain on the System: An HVAC system’s blower motor has to work harder to overcome the resistance from the backwards filter, leading to potential wear and tear or even premature system failure.
• Clogged Filter and Potential Damage: Over time, a filter installed the wrong way can become clogged, further restricting airflow and putting your furnace at risk for damage or a breakdown.

Tips for Maintaining Your Furnace Filter

1. Change the Filter Regularly: It’s recommended to change your furnace filter every 1-3 months, depending on the type of filter and how often you use your HVAC system. A dirty filter will reduce efficiency and make your system work harder.
2. Choose the Right Filter: Not all filters are the same. Be sure to choose the correct size for your HVAC system and select a filter with an appropriate Minimum Efficiency Reporting Value (MERV) rating. Typically, a MERV 8 filter strikes a good balance between air quality and airflow, while a higher MERV rating can be too restrictive for some systems, impacting efficiency.
3. Inspect the Filter: Even if you’re changing the filter regularly, it’s a good idea to inspect it periodically (perhaps once a month) for any visible damage or wear.