Is there a right or wrong way to put in a furnace filter?

Author: Prof. Luis Willms  |  Last update: Thursday, November 20, 2025

Replacing your air filter is not difficult. Remember that air flows from your ducts, through the filter, and into the furnace. The arrow on the filter should always point toward the furnace.

Is there a wrong way to put a furnace filter in?

The direction of airflow in the HVAC system can cause some confusion, and for good reason too! To ensure your furnace filter is put in the correct way, make sure the arrow on the furnace filter is pointing towards the furnace.

How to tell if a furnace filter is backwards?

There should be an arrow on the filter that points in the direction of airflow. Make sure it's not a high MERV filter.

What happens if a filter is put in the wrong way?

If the filter is placed in the wrong direction, the finer pores on the other side of the filter will make it difficult for air to pass through the system. When that happens, there will also be a decrease in the cooling performance of the AC.

What happens if the air filter faces the wrong direction?

If you install your filter in the wrong direction, air will have a hard time flowing through the filter's material and your air handler will have to work overtime to make up for the loss of airflow. This is not only a waste of energy, but it can also possibly damage your air conditioner or heating system.

FURNACE FILTER DIRECTION: How to Replace HVAC Furnace Filter

What if there is no arrow on the air filter?

What if there is no arrow on the air filter? If there's no arrow on your air filter, just make sure the side with the frame (usually the cardboard or metal side) faces the furnace. The flat side of the filter should face the return air duct.

Do I have to turn off the furnace to change the filter?

Changing a furnace filter is simple. First, make sure your furnace is turned OFF so it doesn't blow air when you remove the filter. Next, locate the filter housing on your furnace. This is different for each model, but you can normally find it between the air intake and the furnace.

Which way should a filter face?

They should always be installed with the arrow pointing toward the furnace or air handler and away from the return duct. This orientation ensures that the filter can effectively trap dust and debris before the air reaches the furnace. Install the new filter in the same direction as the old filter when replacing it.

What happens if you forget to put a filter in your furnace?

If you were to use your home furnace without an air filter, all that dust and debris could get stuck in your system and cause a rather large buildup. Over time, these buildups can clog and damage your system. To protect and extend the lifetime of your system, we recommend only running your furnace with an air filter.

What happens if the furnace filter is backwards?

The most common problem you will face with a backwards facing filter is simple inefficiency. If your furnace is forced to blow air through the non-porous end of a filter, it will take more energy to do so. The blower will be overworked and you will pay more money for your heating.

Is there a wrong way to put in an air filter?

When installing the air filter in the HVAC unit, ensure the arrow should always point towards the blower. This direction ensures that the air flows through the filter material correctly, thereby effectively trapping the particles.

What happens if air filter is not put in correctly?

Incorrect filter installation or installing the wrong filter can leave your engine open to dirt and debris. When the engine's air intake is not completely covered by a filtering element, extensive damage can occur.

What happens if a fuel filter is installed backwards?

If the fuel filter was installed backwards, it can indeed cause problems. A backward fuel filter may restrict fuel flow to the engine, leading to increased wear on the fuel pump and potential pump failure. To resolve this, you'll need to remove and reinstall the fuel filter correctly.

What happens if the filter drier is installed in the wrong direction?

Consequences– If the technician makes the mistake of installing the drier in the wrong direction, the drier will not work and serve the purpose for which it has been designed. So, no filtration of contamination and no drying of moisture.

Can the wrong filter damage a furnace?

The blower fan in your HVAC system may not be able to handle anything stronger than MERV 12. A filter that blocks airflow will raise the air pressure in the HVAC ventilation system, which can damage ducts and even the AC and heater.

How do I know which way the airflow is in my furnace filter?

Stand in front of the furnace and look for the ducts. Pull the old filter out and discard it. On the new filter, find the arrow indicating the proper airflow direction. The arrow must face toward the furnace and away from the return duct that pulls the air in need of heating or cooling.

Why do furnace filters have a direction?

It's worth remembering the simple saying, “Just go with the flow.” Make sure that the arrow on the filter points in the direction of air movement. Following this general rule ensures adequate filtration while maintaining uninterrupted airflow through your furnace unit.

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