How To Change Furnace Air Filters? (5 Step Guide)

Do you want to learn how to change your furnace air filter?

Furnace air filters should be regularly changed, usually around 1-3 months.

In this guide, I will go over...

  • How to find your furnace filter
  • Choosing the right size (and MERV rating)
  • And making sure it is a proper fit

Let's get started with this guide!

how to change furnace filter

How To Change Furnace Filters

As a home inspector, I have seen many poorly maintained HVAC systems, and not changing the furnace filter frequently is usually the biggest culprit.

Even though furnace filters are pretty cheap, if a homeowner neglects to change a furnace filter regularly, it won't catch dust and debris, and it may even go around the cardboard frame. Once dust starts going into your HVAC system, it can damage the equipment, and it will run far less efficiently.

Air Quality

And in addition to damaging your equipment, your home's air quality will suffer. Occupants may start sneezing and getting allergic symptoms due to the excess dust in the indoor air.

Changing a furnace filter is usually a pretty simple process, but sometimes it can get a bit tricky. Below are my five steps on changing your furnace air filter...

Read Also: What Are The Top Rated Furnace Filters For Mold?

Step 1. Filter Location

The first step that you need to do is actually locate the HVAC filter which is somewhere along the return duct.

I would immediately check the furnace itself to see if the filter is there. There will likely be a slot or cover that is over the filter (to seal the air flow) and this filter cover may be a few inches wide.

If you don't see it at the air conditioner, then the filter may be behind a return air vent. The return air vents suck in air from the home in order to 'return' it back to the furnace. These return air vents are much larger than the smaller supply air vents that are in the floor or ceiling.

If you still can't find it, then I would go back to the furnace, and take off the HVAC cover. Sometimes the filter is located within the furnace compartment and you will have to take off the cover to change the furnace filter.

Most furnace covers are pretty easy to remove. You will either have to remove a few screws, or there may be a latch that needs to be undone.

Read Also: Does Furnace Filter Thickness Matter?

Step 2. Choose The Right Air Filter

Assuming you haven't already purchased a new filter, it is important to choose the right size filter, as well as the indoor air quality rated in MERVs.

Physical Size

Most standard air conditioner filters are 1-inch thick, but 2-inch thickness is also common. Homeowners should write down the height and length dimensions (as well as the thickness).

You may also have a 'media' filter which is a higher efficiency type that is usually four to five inches thick. These filters can last 6-12 months as compared to the standard 1-inch thick filters that last 1-3 months.

In addition the the physical dimensions, homeowners will also have to pick the indoor air quality that they want.

Read Also: What Are The Best Furnace Filters For Dust Control?

MERV Rating

The industry standard rating of furnace filters is known as the MERV rating, and it stands for minimum efficiency reporting value.

In essence, this rating will tell you how much particles the new filter can remove from the indoor air in a 'worst case scenario'. The MERV rating is always calculated by choosing the lowest performing test and not the highest, hence the term 'minimum efficiency'.

For most homes, I would recommend a MERV rating anywhere from 7 to 12. MERV ratings 13 and higher can capture ultra fine particles including viruses.

Anything above 10-11, I would consider a high MERV rating.

Homeowners should also be careful about buying too high of a MERV rating because it can hinder air flow and may even damage your HVAC system. If you have any doubts, I recommend looking at the HVAC literature for your specific system to see what is the maximum filter MERV that you can go.

Step 3. Turn Off The HVAC System

Before you change the furnace filter, it may be a good idea to turn off the HVAC system. It isn't totally necessary (I don't always do it) but it is a good practice.

At minimum, if the air conditioner turns on when you change the air filter, then any loose debris is going to get sucked into the system. Plus, you may have trouble removing or installing it when the air blowing, and it may even cause a deformation of the filter.

To turn of the HVAC unit, you can simply turn it off at the thermostat. However, most home pros simply flip the emergency shut-off switch at the furnace (all furnaces should have them) which is usually a red box mounted on the wall. If you have a heat pump, there should be a single breaker located on the heat pump that you can flip off.

Read Also: What's The Difference Between MERV And MPR Filter Ratings?

Step 4. Install The HVAC Filter

After you have found the filter, chosen the right size and MERV, it is time to actually install it.

Filter Arrow

There really isn't much to it, but probably the most important consideration is the filter arrow. Every HVAC filter is designed to only be installed in one way, and there is a small arrow on the cardboard edge of the filter. The arrow always be points in the direction of the system air flow.

If you are having trouble determining the direction of air flow, the easy way is to look at where the 'guts' of the furnace or A/C is located. The air filter is always installed before the evaporator coil, blower fan, motor and other HVAC unit components.

The HVAC filter is installed prior to the furnace components so it can catch the dust and debris before it damages the equipment. So all you have to do is install the filter with the arrow facing towards the furnace or HVAC components. The other side of the filter should just be the HVAC duct (with no equipment).

And after you have inserted it, don't forget to reinstall the HVAC cover or the filter cover.

Read Also: What Are The Top Rated HVAC Filters For Odors?

Tight Fit

Homeowners should also verify that the filter is a tight squeeze. You don't want air to go around it, possibly damaging the equipment.

A little deformation of the HVAC filter isn't a big deal, but large amounts of air should not be going around it. There are also magnetic filter covers that you can buy to give the HVAC filter an even better seal.

Step 5: Turn On The HVAC

After you have installed the filter, don't forget to flip the heat pump breaker, furnace emergency switch, or turn on the thermostat.

And once you have turned on the HVAC, you may want to remove the cover just to take a quick peek, and that the filter is properly sealed (and not deformed).

Read Also: What Happens If My Furnace Filter Is Backwards?

Final Thoughts On Changing HVAC Air Filters

Changing a furnace filter shouldn't be a difficult step, it really should just take a few minutes. However, if you have to change multiple filters at the return vents, or if you have to remove your HVAC cover just to get to the filter, it may take several minutes longer.

It is important to regularly change your A/C filter to protect the equipment, and it will also give much cleaner air throughout your home.

Cleaner home air will reduce allergies, and it can also reduce the need to clean the home of dust.

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