Furnace Filter Direction: How To Replace Air Filter The Correct Way

The direction of the air filter or furnace filter is crucial to get maximum comfort with your HVAC products at home or commercial place. Arrow points should be in the direction of the ductwork or air handler, and it varies with Upflow, downflow, and horizontal flow of the furnace position.

To begin with, you can refer to the printed direction to adjust arrow points on the product manual and side of the filter frame. You can follow them according to the wind direction.

  • Look for the arrow points on the air filter.
  • Switch on the blower by selecting the fan options of the thermostat and make it ‘On’ after removal of the air filter 
  • After a couple of seconds, the blower will start running. Place your hand carefully, and you can feel the flow of the air. If not feel uncomfortable checking with your hand, hang a piece of paper, it will flutter with air coming from the blower, and you will have an idea about direction.

Types of Furnaces and Location of the Air Filter

There are three categories of furnaces available according to their placement position. The air filter within the system is always positioned near the intake air blower fan and allows air to flow through the air filter.

Upflow Furnace

Generally installed in the home’s basement area, Upflow furnaces are placed in an upright position. It absorbs air from the bottom or sides of the machine after that air gets heated in the heat exchanger and flows upwards in the house’s ductwork. 

In Upflow furnaces, air filter positions at the bottom of the HVAC product within the blower compartment near the cold air return. The arrow marks should point upwards in an Upflow furnace.

Downflow Furnace

In downflow furnaces, air comes from the top. Air gets heated and flows into the ductwork. Air filter positioned at the top within the upper blower compartment. You will find downflow furnaces in the upstairs or attic of the home.

These are more tall than wide. Arrow points should be in a downward position. Some downflow furnaces come with a V-shaped air filter and require two filters installed within the compartment in a V-shaped position.

Horizontal Furnace

As the name suggests, air flows in horizontally placed furnaces from one side to another. Air enters from one side, heats up or removes heat for cooling, and flows the filtered air through the ductwork on the other side.

Horizontal furnaces come with a slide-in-filter within the HVAC unit. Filter stays on the sides that intake cool air. The air pointers should be in the direction of the airflow.

We now explained the required direction for Horizontal, Downflow, and Upflow furnaces. It’s time for important questions and answers that you need to know as a consumer.

Why Does Airflow Direction Matter At The Time of Air Filter Installation?

HVAC products are designed with an air filter on one side that is comparatively more porous than the other side of the unit. Air filters absorb maximum pollutants and minute particles and ensure optimum airflow.

What Happens when you Install an Air Filter in the Wrong Direction?

The air filter in the wrong direction is bad for multiple reasons. First, the machine has to work overtime to provide a comfortable indoor atmosphere. It will take lots of time to heat or cool or filter out dust particles, etc. Therefore, it will consume more energy and inflate your monthly utility bills.

In addition, if it stays in the wrong direction for a long time, your furnace will start to malfunction gradually.

How to Ensure the Correct Direction of the Air Filter?

Airflow direction should be towards the blower and away from the supply duct. Position and direction vary for Upward flow, Downward flow, and Horizontal flow types of furnaces. HVAC manufacturers print the directions to keep the arrow pointers according to the airflow on product sides.

You can also check online resources for guidance or ask the technician who installed your unit.

What are Furnace Filter Ratings?

Furnace filter ratings are a measurement of its efficiency, and there is a minimum requirement fixed by the United States Environment Protection Agency to be maintained for HVAC manufacturers.

It is a rating on the scale of 1 to 20 using the MERV (Minimum Efficiency Reporting Value). All manufacturers need to maintain US Government recommended range of 7 to 13 MERV ratings for air filters.

How To Choose The Best Furnace Filters For The Home?

A good furnace filter depends upon use and budget. Research says air filters with MERV ratings 7 to 8 consider as perfectly balanced for cost and efficiency.

If you properly understand the MERV, check ratings on the product manual. It is advisable to consult the HVAC product supplier and ask about the correct air filter according to budget and consumption.

A balanced filter is essential because a high MERV-rated filter can slow down the airflow, and low MERV ratings will struggle to eject dust properly. The desired air filter should screen out around 85 to 90 percent of the pollutants and debris with particles as small as 5 microns.

How Do I Know If The Air Filter is Dirty and Needs Replacement?

To start with, make it a habit to check your machine regularly for dirt and debris accumulation. A common and often ignored reason for HVAC product malfunction is dust everywhere at pores, parts, etc.

A dirty furnace releases a significant amount of air pressure due to debris congestion. You can also install the filter monitoring system and get a notification for increased dust within the machine.

If your machine shows reduced efficiency due to accumulated dust and debris, it is time to check the air filter and replace it with professional help. HVAC products are technical stuff, and DIY methods might be counter-productive in terms of further damage to the entire unit if you lack technical knowledge about its mechanics.


HVAC products are engineered for optimum energy efficiency at home with dedicated functions for each part and technology. You need to carefully read the user manual and ensure the correct position of all components at the time of installation. Keep the air filter according to the above-given instructions and enjoy a cozy indoor atmosphere.

Related Articles You May Like

Scroll to Top