Questions & answers about the location of heating or air conditioning or heating system filters.

HVAC air filter location, placement, or similar problem questions & answers are discussed here.

Page top photo: this attic air handler probably includes an air filter at its right end where we see the return air duct connected to the blower unit.

This article series explains in detail how to find the air filters on an air conditioning or hot air heating system.

FAQs on Where & How to Find the Air Conditioner or Furnace Filter

If you can't find your air conditioner system filters (there may be more than one air filter) some places to look are given at .

The questions & answers below about where to locate the air filter in air conditioning, heat pump, or forced-air heating systems were posted originally

at AIR FILTER LOCATION

I don't see an air filter anywhere on my system

Great article. I've been trying to find the filter(s) for my ac unit. I cannot find it. Maybe it is inside. I will check.

The unit is in the basement and fit to my 80+ years old house by the previous owner. It looked very much like the photo in the "Watch Out: If a building air conditioning or heating system air handler gets its return air right at the air handler" section.

And it also has a register at the bottom. The return duct is there just like it is in the picture.

But It stops about 15 ft from the unit and is closed at the end. I don't see it connecting to any of the rooms.

So I wonder if my AC unit wasn't properly installed. BTW, somehow the register at the bottom blows out air instead of sucking in air. So I am not sure where the unit gets the air from. - On 2011-08-01 by jzw

I can't locate the filter for our Payne central AC. I checked the intake vents, but no luck. Where is it? - On 2016-07-20 by Anonymous

Reply by (mod) re: where is the furnace or air conditioner air filter usually located

Typically the filters are at the return air inlet. If you found them there there may be no other filters at the air handler itself.

For more detailed help finding the air filter(s)

see AIR FILTER LOCATION - topic home

More tips on finding the air filter

JZW

Sometimes we see a system installed with no air filter whatsoever. If you find that's the case in your system, you'll want a filter installed - at a location that is easy to access so that folks will actually change the filter on schedule.

And check the blower fan assembly - if there was no air filter, or the filter was left very dirty for a long time, or was leaky, the blower may need cleaning.

You should not feel air coming OUT of the return register. If you do, something is blocked (or it's not the return register).

@Anonymous: From just your one line e-query, Anon, nobody can say where your system's air filter is located.

But AIR FILTER LOCATION - topic home suggests where to look. Follow the ductwork; check the air handler, check the return registers.

How do I know if there is more than one air filter on my air conditioner?

I have a York unit, the model is a f2rp036h06g, not a window unit, maybe a 1 ton to 1.5 tons. house was build in 2005.

I have changed the one in the ceiling, but is there a second one and where ? - On 2014-07-10 y Juan

Reply by mod

Start at the air handler and look for an air filter at its return air inlet (duct connection), in the air handler itself, and at its supply air outlet; then follow the ductwork, noting the location particularly of all of the return air inlets. You should find either a filter right at the air handler or one at each return air inlet grille.

I can't even find the air handler or blower unit itself

I have a 1st floor condo unit. The condenser is outside but there is no air handler in my unit. There is no access to a crawl or attic space. I only have a thermostat and have no idea where a filter would be located.

I have ductwork for AC. Heat is from baseboard/boiler in basement of building. - by Elaine -

Reply by (mod) re: where to start if you can't find the air handler or blower unit

Elaine you should be able to spot where cool air comes INTO your unit (supply registers) and where warm air is LEAVING your unit (the return register) - typically one or just a very few larger grilled openings. That latter is where to start looking for an air filter.

If your air handler is in the building basement, that's a place to look: at the connection of return air to the air handler or inside the air handler or blower unit itself.

 

Where is the air filter located on a Goodman furnace?

I have a Goodman where is the filter located? - by Mario

Reply by (mod) - Here is information on Goodman furnaces, manuals, and the air filter location

Mario,

The air filter location on a heating or air conditioning system is not absolutely-fixed. The air filter is often right at the air handler unit or "blower unit" but it could located with equal probability elsewhere in the building such as at the air inlet grille of a central air return.

The article above - this page - includes suggestions for finding the air filter on your system.

In essence, follow the air flow.

Start by identifying the air return inlet - there will be one or more. If there is no filter there, find the air return duct connection to the air handler. Look there.

If there is no filter at the air return plenum where the return air duct connects to your air handler, then the air filter is likely to be inside the air handler: there will be a door or handle that can be turned or lifted to open the air handler

Watch out: TURN ELECTRICAL POWER OFF FIRST to AVOID INJURY

In the article above try reading the section titled

A Detailed Guide on How to Find the Air Filters on an Air Conditioning or Heating System

Here is an excerpt from a typical Goodman Air Conditioner manual [PDF]

10 Return Air Filters

Each installation must include a return air filter. This filtering may be performed at the air handler using the factory filter rails or externally such as a return air filter grille. When using the factory filter rails, a nominal 16x20x1”, 20x20x1” or 24x20x1” (actual dimension must be less than 23-½”x20”) filter can be installed on a B, C and D cabinet respectively (the cabinet size is the seventh letter of the model number).

If you don't have the manual for your Goodman air conditioner see GOODMAN HVAC free manual downloads

On a typical Goodman air handler, the front lower door can be removed by sliding up and lifting it out to give access to the air filter.

Can a new Carrier condenser be located 1-inch from the wall?

Can a new Carrier unit be located only 1 inch from the wall.? The other 3 sides have over 12 inches of space. Will the close location effect the efficiency of the new unit? - On 2017-07-08 by Sylvia Wahoske

Reply by (mod) - no

No, Sylvia, that distance violates just about every manufacturer's installation instructions and guidelines - unless perhaps you have a piece of equipment rated for "zero clearance" - not something that I've seen. But this isn't an air filter question.

Details about clearances around HVAC compressor/condenser units are

at CLEARANCE DISTANCE, HVAC

 

Does it matter if my A/C filter opening is behind the door?

I have a A/C filter vent behind a door. Is this a good place or is it defeating the purpose? the room is an external room that leads outside and with the door open it covers the vent. - by M

Reply by (mod) re: avoid installations where doors will block air inlet to the air filter or return air

M

When the door is open it blocks the return air - that is certainly going to increase the cost of operating the system and reduce its effectiveness too - the air flow will be restricted.

Can you put a door stop on the floor so as to keep the door a foot or more away from the return air opening? That'd help.

 

Why are there three air filters on my home's HVAC system

Hi, I just purchased a new home and when changing the largest of the three return filters I noticed there was a secondary filter inside the largest return. It is not two stacked on one another, there is a second slot to hold a filter that is perpendicular to the primary filter inside the return.

The primary filter is a 20*25*1 and the secondary filter is a smaller 10*10*1.

The other two returns in the house are 14*20*1 and do not have a secondary filter inside the return.

Unfortunately, I am at the office and do not have any specs for the HVAC system other than it's a Trane, so I know that doesn't help much.

Just curious how this setup works and why it is there. - On 2017-04-19 by Tacoman

I just in the last few months moved into a new mobile home. I have 3 filters inside my a/c return register, 2 of them are metal that resembles the filter in the hood of a stove & 1 regular type filter.

The regular one I change every time I pay my electric bill but the 2 metal ones I am not sure how to clean.

What is the purpose of the metal ones. Have never lived in a place that has used these. - On 2016-09-20 by Terry DuBois

Reply by (mod) cascaded air filters can be cleaned

Some HVAC system use use a cascade of air filters. Typically the first filter is one that can be removed and washed.

Let's get the IO manual for your furnace to see what the manufacturer says you should do.

 

The AC tech told me to not install a filter at the furnace if I have filters in the return vents

I live in central Florida and I have 2 return vents. One in the hallway 20x21x1 and another in the master bedroom 12x12x1.

I also have a furnace with a slot that I could install a filter.

My question is, do I install a filter at the furnace or at the return vents?

The AC tech told me to not install a filter at the furnace if I have filters in the return vents because that will make the system work harder? - - is he right?

Do you recommend a filter at the furnace versus the return vents? - On 2016-10-02 by Macster

Reply by (mod)

I think your technician is correct.

 

Bryant A/C BB5600 is blowing air into my flat (and dust) but no cool air

I'm renting and this house has a Bryant a/c unit model BB5600240000e00 regardless the landlord has it pushing air into my flat even though the air isn't working.

I'm getting all kinds of dust in the house and have asthma and COPD. Something is putting air in here and its making me sick. - On 2016-06-13 by Anonymous

Reply by (mod)

Anonymous:

You can turn off the A/C fan at the thermostat or at the air handler unit until the A/C system has been repaired.

You should be sure that a clean air filter is in place - or at least whomever is maintaining the A/C system should do so.

You could block air flow or at least reduce it significantly by closing your supply register louvers.

Your landlord may be worried about indoor mold due to hot humid air, high indoor humidity, low air movement and may be running the fan as a stopgap measure. Discuss these concerns with your landlord.

 

Why does the blower run when the air conditioner is not on?

What is causing the air to blow if the air conditioner or the heat pump isn't cooling - by Nancy

Reply by mod

The thermostat FAN ON switch may be in the ON position
or

The thermostat is calling for cooling and the air handler runs but your outside compressor/condenser won't.

See DIAGNOSTIC GUIDE A/C or HEAT PUMP for some simple steps to follow.

 

Are filters needed on both the return air inlets and at the air handler

I have a unit that is similar to that above in the first picture with the very dirty filter. Do I need to have filters on the return grilles as well? - are filters needed on both the return air inlets and at the air handler. On 2016-05-14 by Hilda

Reply by (mod) - No but can be acceptable in some installations

No, Hilda. And unless the ductwork, air handler blower unit, and system are designed to push enough air that air filters in two locations, doing so may restrict air flow more than is acceptable.

 

I am not sure where the air filter is located on my air conditioner / furnace

I have two carrier air conditioner units, horizontally placed in my attic. I am not sure where the filter is located within in the unit.

I could take a picture and send you a copy if that would make it easier to locate the filters. I have replaced the filters at the ceiling register units. One unit is a 4 tons and the other is 5 tons. - On 2016-02-08 by Stoddard Best -

I can't find the filter on a Goodman package unit looked every where may not be one in how do I no where to put one in - On 2016-05-31 by sho

My Lennox central ac is installed on the roof , but the air filter needs to be changed in the attic ; I can't find the air filter in the attic which supposed to be under the ac unit . - On 2016-05-18 by Allen k

 

Bryant heat pump has the air filter on the return side - gets wet from condensate

I have a central heat pump with air conditioning and heating assist. On my Bryant system, they placed the filter in a very odd place. It is on the return side, but during the summer months, the refrigeration coils drip condensation water all over the filter because it is right below it.

Half of the filter also gets sucked up into the plenum chamber where the A-frame coils are located, too. Consequently the air flow gets restricted, and the coils start to ice up causing even more water to drop down to the lower part of the intake plenum chamber.

Plus, when I go to remove the filter to change it, it is all warped out of shape, and usually damp, and hard to remove out of that little opening after removing the little access door. Whatever particles were on the filter will now drop down to the lower chamber as I try to remove the filter.

It seems to me that the filter should have been installed away from those coils, and on the other side of the return plenum where it is dry, and a larger area for the filter. Why did they put the filter t On 2015-07-20 by Heat pump Air Conditioner/Heater systemere? -

Reply by (mod) - a wet air filter is a disaster

Actually it's quite common to put the air filter at the return side of the system - removing airborne building dust before the air passes through the blower fan (where it'd clog it).

But if your filter is getting wet from A/C condensate then some repair work is needed to determine why and then to fix that. I agree that a wet air filter is a disaster: it won't filter, it'll block air flow, and it risks growing mold as well.

Let's get a service tech on site to see why the condensate isn't being properly handled, collected, and drained. - Daniel

 

Question: Should I remove the air filter installed at the air handler and just filter at the return air inlets?

My house has a central air unit and 2 return supply grills in each hallway. I always had a big filter in the main unit (16x20x4) and then one in each of the return grills (16x25x1).

Last year my unit was not cooling very well and the tech said I should not have filters in all 3 spots, and suggested I not put one in the main unit, just the hallways.

Now the house cools great, but the dust is over whelming. Is there some adjustment I should make by adding a central filter again, or just buying super efficient hallway filters? BTW, we have lots of pets.

Rox5704

Reply: Suggestions for filtering HVAC air at the return air inlet grilles

Rox:

In my OPINION what your HVAC tech said was reasonable.

I would NOT want to operate an HVAC system with no air filters - doing so leads to debris collection in the duct system (expensive to clean or correct later on) and debris clogging at the cooling coil of an air conditioner and debris clogging on the blower fan - reducing airflow further and creating system operating problems.

The problem with filtering ONLY at the air handler is that debris collects in the ductwork, especially the return ducts - that can be costly or even impossible to clean, depending on duct routing and the materials used.

So it's best practice to filter return air right at the return air inlet grilles just as your tech suggested.

You can try using higher efficiency filters at the return inlets (the inlet mounting grille may need to be changed to accommodate a thicker air filter) but choose your filters carefully. A thicker filter that is deeply pleated, by providing greater total surface area than a more flat air filter, can improve air filtration significantly without reducing the air flow rate through the device.

What to do if the air filter is at an inaccessible return air inlet?

I have a air handler where there is no filter on the unit itself. There are 2 return ducts into the unit. In the ceiling where one return duct originates, I am able to easily reach and change the filter. The 2nd return duct origin is 18 feet high and has no accessible filter. Any suggestions?

Do I have to get a ladder every month as well as change the cage so a filter can be placed, is having a filter on one return enough? Is it better to "add" a filter to the main air handler unit? Thanks. - On 2014-09-05 by Doug

Reply by (mod) - If you don't change the filter you obstruct air flow, increase cooling or heating costs, and potentially cause coil icing

Doug, yes if you don't change the filter you obstruct air flow, increase cooling or heating costs, and potentially cause coil icing (loss of cooling).

If you eliminate the filter that's hard to reach you ultimately dust-clog the blower fan, cut its air movement ability, and increase system operating cost.

Ask you HVAC technician if you can get by with an air filter just at the air handler itself

 

Which side of the air filter goes on the support webbing?

Real simple:16x25x1 pleated air filter,which side goes on the unit w/the webbing?

Does the soft side go in facing the unit itself ? Right now the soft side is the dirtiest - On 2014-07-03 by Rosetta

Reply by (mod) - which way does the air filter face?

Rosetta,

The air filter will have arrows on its edges indicating the direction of air flow through the filter. Install the filter so that air will flow in that direction through it.

The concept is that the reinforcement that prevents air filter collapse would go on the "downstream" side of the air filter so that it can resist the air filter being pushed in that direction by the airflow.

Another clue besides air filter direction arrows:

On many filters one side has reinforcement on the air outlet side of the filter to prevent its collapse due to air pressure.

Watch out: It is important to respect the air filter's air flow direction requirements since installing an air filter "backwards" can allow the filter to collapse and become sucked into the HVAC system where in some designs the result can be a jammed blower fan, an overheated motor, and even a fire.

Do we need air filters both at the rooftop unit and inside of our suite?

I have questions regarding the filters for a commercial AC unit. We were told that our 2012 and 2013 units don't need filters inside our suite but rather the filter is inside the roof top unit.

We also have a 2008 unit and for that we were told that we do need to change the filters inside our suite. We were also told that this is because of new regulations. So which filters should we be changing quarterly?

We currently have filters at the roof top units and we also have filters in all the registers. Is this choking our AC systems? - On 2014-05-02 by Anonymous

Which is better: air filters at the rooftop unit or air filters at the return air inlets in our apartment?

I am installing a new gas pack.

One company suggested a unit with the filter at the air handler on the roof (as it is now).

The other will install 2 filters at the returns. I have quite a bit of duct work on the roof, so the first suggested having the filter at the handler is more likely to filter out more as dust can get into the duct work along the path to the handler. Which is better? - On 2013-02-27 by Rebecca

Reply by (mod) - watch out for excessive filtration

@ Anonymous: You should follow the instructions of your HVAC service technician or installer or other building expert, provided that they have actually inspected your specific air conditioning system.

I agree that if you install more filters than specified in the system's design, you may obstruct air flow and increase the system operating cost. - Daniel

@Rebecca: in addition to my advice to Anonymous above, I add that in your case, as Mark Cramer says " ... it depends"

If you are the people who are supposed to be changing your system's air filters monthly and if the return air inlets are readily and safely accessible inside your suite then that's a good place for air filters.

If the building maintenance staff are going to be the people replacing air filters, I'd bet a six-pack of Castle Danger beer that they prefer the rooftop access point so that they don't have to disturb you simply to check or change the unit air filters. - Daniel

 

Recommended air filter locations when we have a lot of animal-hair-shedding pets vs too many filters?

My house has a central air unit and 2 return supply grills in each hallway. I always had a big filter in the main unit (16x20x4) and then one in each of the return grills (16x25x1).

Last year my unit was not cooling very well and the tech said I should not have filters in all 3 spots, and suggested I not put one in the main unit, just the hallways.

Now the house cools great, but the dust is over whelming. Is there some adjustment I should make by adding a central filter again, or just buying super efficient hallway filters? BTW, we have lots of pets. - On 2011-11-03 by rox5704

Reply by (mod) -

Rox:

In my OPINION what your HVAC tech said was reasonable.

I would NOT want to operate an HVAC system with no air filters - doing so leads to debris collection in the duct system (expensive to clean or correct later on) and debris clogging at the cooling coil of an air conditioner and debris clogging on the blower fan - reducing airflow further and creating system operating problems.

The problem with filtering ONLY at the air handler is that debris collects in the ductwork, especially the return ducts - that can be costly or even impossible to clean, depending on duct routing and the materials used.

So it's best practice to filter return air right at the return air inlet grilles just as your tech suggested.

You can try using higher efficiency filters at the return inlets (the inlet mounting grille may need to be changed to accommodate a thicker air filter) but choose your filters carefully. A thicker filter that is deeply pleated, by providing greater total surface area than a more flat air filter, can improve air filtration significantly without reducing the air flow rate through the device.

Followup by rox

thanks so much. this makes sense. I will buy better quality filters for my hallways and leave the central unit alone.

Can I move the air filter from the air handler to the return air register inlet

Hi, I have a furnace that's located in a hallway. I have to take the top cover of the heater off first before I can take off the cover of the blower underneath, in order to replace the filter.

My question is can I move the filter from under the blower and place it at the return register?

There are 4 airtight dry walls under the blower - will I need to add a return air plenum? Right now the filter is 14x24 inches and I am trying to make it bigger (20x30) if possible. - On 2011-08-22 by ly2240

Reply by (mod) -

@Ly,

Yes you can install an air filter at the return register;

You might want to check the ductwork for cleanliness and if it's dusty dirty it'd be smart to clean the ductwork when you're changing the point of air filtration.

HVACR suppliers sell return air register grilles that replace a simple flat cover that you may already have. The new grille unit will include a recess intended to support an air filter.

And make sure ALL of the return registers get air filters if there is more than one.

There is no air filter in my heating/cooling system, and my A/C isn't cooling the house

I will check these places when I get home. My landlord said the builder told him there was no filter in the heating and cooling unit.

I found this cannot be right. My ac is working but not cooling my house. This house is only 3 years old!

I will check over everything and hopefully I will find the problem myself. Been waiting on the repair guy for 3 days! - On 2011-06-02 by PAM

Reply by (mod) -

Pam:

If you say your AC is "working" but is not cooling the house, I interpret that to mean that the system is "running" but not really "working" properly.

Either there is inadequate air flow or the air flow is OK but it's not being cooled and dehumidified.

Diagnostic suggestions are found in detail at DIAGNOSTIC GUIDE A/C or HEAT PUMP 

 

Thank you to our readers for their generous comments

On 2015-05-27 by Anonymous - Very helpful and detailed article, thank you.

On 2011-08-01 by jzw Great article.

...

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Air Filter Articles

• AIR FILTERS for HVAC SYSTEMS
  • AIR FILTER EFFICIENCY
  • AIR FILTERS, FIBERGLASS PARTICLES
  • AIR FILTER LOCATION
  • INSULATION BLOCKED COOLING COIL
• AIR FILTER MATERIAL RE-PURPOSED for FACE MASKS
• AIR FILTER OPTIMUM INDOOR
• AIR FLOW IMPROVEMENT, HVAC

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