Changing the air filter in your AC or furnace can seem like a simple task.
But there is one critical thing you need to know – which way does the air filter go?
The arrow on your air filter should point to the blower in your HVAC unit. If the filter is in the wall or ceiling in your home, then the arrow on the filter should point to the wall or ceiling.
In this article, I’ll help you figure out which way the air filter goes in your home’s HVAC unit. I’ll also go over how to check the airflow direction in your AC or furnace.
Which way does the arrow go on an air filter?
Most air filters have an arrow printed on their side that indicates the direction of airflow.
The arrow should point in the same direction as the airflow in your HVAC unit.
- If you are installing the air filter at the HVAC unit, the arrow should point to the blower.
- If you are installing the air filter in a ceiling or a wall, the arrow should point to the ceiling or wall.
Here’s a tip for you: After figuring out which way the arrow should point, draw an arrow on the filter slot. Now you can just match up the arrows next time you change your air filter!
What happens if you put the air filter in backward?
If you put the air filter in backward, then you run the risk that the filter will implode and damage your HVAC unit.
The air filter is not designed to be put in backward since the filter material only filters properly in one direction. There are multiple layers of mesh in the air filter. These layers increase in density towards the downstream side of the air filter, which allows a higher filtration efficiency.
You’ll suffer from reduced filtration efficiency in your HVAC unit if the filter is backward.
In addition, the metal mesh that holds the filter together only works if the filter is installed in the correct direction. If the filter is installed backward, you risk the filter imploding on itself when your HVAC unit turns on.
Which side does the air filter’s metal mesh face?
The air filter’s metal mesh should face the blower in the HVAC unit. If the filter is in the wall or ceiling, then the mesh should face the inside of the wall or ceiling.
The metal mesh should always be on the downstream side of the airflow in your HVAC system.
What is the purpose of the air filter’s metal mesh?
The metal mesh on a pleated air filter is used to keep the air filter together. When air flows through your HVAC system, the air filter is subjected to strong pressure. The metal mesh holds the air filter’s filtration media together.
Pleated air filters are made of a pliable material such as polyester or cotton. The soft air filter material would stretch out if it didn’t have anything to hold it in place. The metal mesh also prevents the filter material from fluttering while air passes through it.
Which way does the air flow in an HVAC unit?
In an HVAC unit, the air flows from the return duct, through the HVAC unit, to the supply duct. In a residential central AC or furnace, the air almost always flows from the bottom to the top of the HVAC unit.
How do you figure out which way the air flows in an HVAC unit? Here are some methods:
One method is to inspect the ductwork attached to the unit:
- The supply duct will sometimes have insulation around it. If one duct is insulated but the other one is not, the insulated duct is most likely the supply air duct.
- If none of the ducts are insulated, you can put your hand on them to feel the temperature. If you are running your furnace, then the supply duct will be hot. If you are running your AC, then the supply duct will be cold.
- If you have central AC, then the AC evaporator coil is located in the supply duct.
Once you know which duct is which, then you can figure out which direction the air flows.
Another method is to examine the location of the air filter slot in the HVAC unit. The air filter is always located in the return air duct. The airflow direction is from the air filter slot to the HVAC unit.
Shoud I be hearing a ticking sound from my HVAC system. Or is that what happens when it is working properly
Hi Ronald,
It depends on what is causing the ticking sound. A quiet ticking sound from a blower spinning usually isn’t of too much concern, but it might be worth getting it checked out by an HVAC professional to ensure that everything is working correctly.
Cheers,
-Trey
The arrow in the air filter looking at the unit should be pointing to the unit itself which is on the right side …am I correct?
Hi Joseph,
Yes, the arrow on the air filter should point to the unit itself.
Hope this helps,
-Trey
Ok I see a mixed message on all of these sites on filter direction. I have an arrow on my filter so I have the arrow pointed toward the furnace away from the return duct; however, this site and others say that metal part in the filter should be closest to the furnace. What happens when the arrow points opposite of that thinking? Meaning the arrow points away from the metal mesh side, meaning I have the metal “screen” side away from the furnace and not closest to it.
Hi Todd,
That’s strange. The arrow should always point toward the side with the metal screen. The purpose of the metal screen is to keep the filter intact, so it wouldn’t help if the screen were on the opposite side.
I’m wondering if your filter is defective. I would reach out to the filter manufacturer for clarification from them.
Hope this helps,
-Trey
I, too, have the same issue as Todd. The ceiling filter I’m installing is a Filtrete. If I put the filter’s arrows pointing towards the blower, the mesh wiring is on the outside facing the floor. I bought a six-pack from Amazon and all are constructed like that. Could all six be duds? I thought it very odd when I looked at the filter and that’s what brought me to your site. Has anyone else had this issue using that brand? Thank you for any help you can provide.
Hi Clancy,
There have been multiple comments on my website regarding the arrows on Filtrete filters so i’m wondering if there is a batch with the mesh on the wrong side, or if that’s how those filters are manufactured now.
What specific model of filter do you have?
Thanks,
-Trey
I have watched so many youtube videos with instructions on how to replace the air filter in HVAC systems but can’t find anyone showing how to replace one that is on the front of the system and is just put in a slot that is at an angle. There is no door on it or compartment that it’s in.
My HVAC is located in a utility closot in my condo. The closet door has vents on it.
I noticed that the filter was getting a darker color and I was beginning to get a cough every time the unit went on. I have a lot of allergies.
I told the manager and she replaced the filter. While doing so, she commented that the last filter was facing the wrong way. It had the arrow pointing toward the actual unit. She put the new fiter in with the arrow pointing toward herself away from the unit. so if a person is facing the furnace the arrow is pointing toward them. I am concerned that the filter was put in the wrong way by her. The metal mesh is on the outside of the filter where I can see it.
Do you know what is the correct way to place the filter on this type of unit? Should the arrow on the filter be facing toward the unit or away from the unit and facing the person putting it into the slot? Thank you!
Hi Susan,
The manager is wrong. The arrow on the side of the filter should point towards the unit. The metal mesh should be on the interior side of the unit, where you can not see it.
-Trey
I’m glad I found your website and asked. Thank you for such a quick reply!
Hi Trey,
I recently replaced the filter of my air handler. I have the AC and heat off, and just the fan running.
I can feel air flowing through the filter to the ground (away from the unit). Is this normal? I thought I should feel a suction since the unit should be pulling air in through the filter.
Thanks!
Hi Adam,
Yeah, that’s unusual. The air pressure at the filter should be negative relative to the outside of the unit. Are you sure that air isn’t sucking into the unit? It can sometimes feel as though air is blowing out, even when its sucking in – that throws me off sometimes too. Try holding up a tissue or piece of toilet paper to the area where you feel the airflow to check the direction of the airflow.
Hope this helps,
-Trey
Hi, my air filter is located on the bottom of the ac unit inside. Would the arrow point toward the unit or the floor? I have it facing the unit.
Hi Kim,
You are correct, the arrow on your filter should point up towards the unit.
-Trey
My filters in my HVAC unit always fall down inside. The access panel says to use a 15X20x1 size but it is in there kind of loose. Before a month is over, the filter comes loose off the tiny tabs on the side of the filter track and drops down onto the floor. I have to use a coat hanger to fish it back out of the slot. What is going on?
Hi Amanda,
Depending on how the filter slot is made, you may be able to modify it so it holds your filter a little more snugly, or get an HVAC professional to do that for you.
One question I have is what is the MERV rating of the air filter that you’re using? Air filters with high MERV ratings generally restrict more airflow, especially 1″ filters. The bowing of the filter from the airflow restriction will cause your filter to cave in and fall out of its slot.
Hope this helps,
-Trey
My unit is inside with the filter holder at the bottom. When I install it, the arrow is up and the wire mesh is also up. Is this right? Thanks
Hi Kathy,
Assuming that your unit blows out of the top, then yes that it the correct orientation for the filter.
-Trey
Hello All,
I have an ac unit that is in my attic. On my unit there is an arrow and the word airflow on the door. So I placed my filter in the unit with the arrow facing same direction. My question is should the filter arrow actually be facing the opposite direction of the airflow arrow.
Hi India,
The arrows should both face the same direction
-Trey
I’ve owned my home for 29 years. Fingers crossed, my original old-school (freon-based) whole house central AC system still performs. I run my AC from June through at least September. Too, I often run it in simple fan mode the other months. For as long, I’ve been religious about replacing my 20x25x1 Filtrete filter every month during summer and every 3 or so non-summer. At first, it wasn’t clear to me which direction the air flow went. And the internet didn’t exist yet on such subjects. After a few months, I realized installing the new filters in one direction resulted in nearly pelts of debris and pet hair on the filters’ baffling, whereas installing in the other ‘caught’ almost nothing. So I marked my AC housing’s case with the best-catching filter arrow direction, for all subsequent filter changes. My findings were exactly what you’re saying.
Hi. My AC filter is located directly in front of the furnace; there is a slot for me to slide the filter into. I have the arrow facing up towards the furnace, however the mesh metal side is on the outside towards me. I have a Filtrate air filter and the arrow on it is facing opposite of the mesh metal side. I was just wondering if one, am I placing the filter in correctly? and two, if it’s okay that the metal mesh side is on the outside? Thank you in advance.
Hi Joanna,
The arrow on the side of the air filter should always point towards the metal mesh