Why Does My Central Air Have Two Filters?

Let’s say you just moved into a new house 3 months ago and it’s time to change out your air filters. You go to look in the usual spots for air filters, and to your surprise, you find filters in multiple locations!

Not to worry! Most central air heating and cooling systems have 2 intake vents that help circulate your home’s air and clean out any debris by running it through an air filter. Depending on the size of your home, you may have more or fewer intake vents, but for most dwellings, the central air system is served by 2 air filter-covered intake vents.

Let’s dig a little deeper into why you might find 2 air filters in your home’s HVAC system.

Your Home’s Central Air System

If you have a central furnace and/or AC system in your home (as opposed to ductless systems), then your system is likely composed of the following 3 air circulation components:

Air Handler

image of an air handler, part of central air system - Filterbuy

This is the metal box that contains the fan, fan motor, condenser coil, and compressor – many of the crucial components of your air system that allows warm air in and cools it before circulating it through the house. These are typically located outside your home along an exterior wall.

Heating/Cooling Manifold

This is the internal system that cools or heats the air by passing it through a set of hot or cold coils, changing the temperature to the desired range set by your thermostat. This central air component also typically contains the blower, evaporator coils, and furnace.

Air Duct System

a man changing an air filter on the air duct system

Your home’s AC air duct system does two things:

Air from the outside the home is drawn into the unit, chilled or heated to the right temperature, then sent into the home
Air from the home is pulled back through the return ducts, chilled or heated to the right temperature, then sent back through the duct system into the home. This helps keep air flowing throughout the home and keeps your temperature stable

Understanding the parts of your central air system matters because it helps explain instances of multiple air filters being used in various places.

When You Need Two Air Filters

There are multiple cases when multiple air filters are needed.

Scenario 1: Your HVAC system has multiple return ducts.

This is the most common reason why your central air system has two air filters. If you live in a big-enough home, condo, or apartment, you’ll have multiple return ducts to effectively recirculate air across the entire home – after all, nobody likes stuffy rooms and irregular temperatures.

Having multiple return vents solves this problem, but it also requires air filters at each vent to properly filter the air and prevent particulates from getting into your fan motor.

Scenario 2: You have 2 air filters because your system has a return duct and an “air handler.”

This setup exists for a few reasons. The lifespan of filters differs, so the number of times you need to replace air filters in the return duct versus the air handler varies because they are sized differently.

For example, the most common size filter for return vents has a depth of one inch that are designed to contain one inch air filters. By contrast, if you look at our filters specifically designed for the air handler, they have an air filter depth of four or five inches. Because the air handler filters have more filter material by virtue of being larger, they can collect and hold more dust, pollen, and smoke before they need to be changed.

Scenario 3: You have multiple central air systems, and each requires separate filters.

This is especially common in two-story homes, where it is easier to regulate temperatures across individual floors. This will mean you have more than one air handler filter, and you will likely have multiple return vents – at least one for each duct system per HVAC system

How to Find Your Air Filter Intake Vent

Now that you know why you have 2 air filters in your HVAC system, let’s identify where they’re located.

For most standard home HVAC systems, there will be a large vent located near the air handler in your home. These vents can be a wide range of sizes, but they’re generally bigger than the air vents that release air to the home (which usually have dimensions similar to a piece of paper).

intake filter vent on a home air circulation system - Filterbuy

For more information on how to find your air filters, read our article on different air filtration systems.

Changing Your Air Filters

Now that you know where you must look to find all your air filter replacements, you are on your way to breathing cleaner, better air in your home.

If you find you need multiple air filters, you don’t need to buy from multiple stores – simply find your air filter sizes and your central air system brand on our site to buy the type and quantity you need. If it’s your first-time installing air filters, make sure to read up on these resources to buy the right products and get it working correctly:

Air Filter Intake Vents FAQs

Do I Need Filters in My Return Vents?

Yes, you need to have properly sized air filters in your return vents. Not only does this help clean the air circulating throughout your home, but it also helps your central air unit run efficiently.

How Many Air Filters Does a House Have?

Typically, a house will have 2 air filters in their intake vents. In some cases, there can be more or fewer depending on the square footage of the home or apartment and the number of floors that need to be supported by the central air system.

Should You Layer 1-inch Air Filters?

In some cases, your intake vents or air handler vents have a filter depth greater than an inch. Because 1 inch air filters are the most common, some homeowners may think it’s okay to layer 1 inch air filters to fit a 2-, 3-, or 4-inch air filter slot. It’s not recommended to do this.

It’s worth calling out this piece of advice from a Houzz forum discussion – if you see a return duct that can accommodate a 2 inch or 4 inch air filter, but has multiple 1 inch filters stacked on top of one another to fit the slot, get rid of this setup immediately. It is questionable if it works the same way as one 2-inch or one 4-inch air filter in terms of filtration effectiveness in working with your central air system.

Additionally, its more expensive to buy air filters this way. For example, a 16x25x1 air filter from Filterbuy costs $22.66* if you buy two filters – by contrast, buying one 16x25x2 air filter costs $17.58* - a much better deal.

* pricing is current as of 2021 – prices may have changed since the publishing of this price

How Do I Clean an AC Intake Vent?

By regularly replacing your intake vent air filters, your intake vents should stay relatively clean. In cases where dust builds up, you can easily remove it with a vacuum attachment, duster, or broom. In cases where there is a substantial amount of dust and debris on your intake vent, the vents can be removed and cleaned with a hose or pressure washer.

How Do I Keep Dust Out of My AC Intake Vent Cover?

The best way to prevent dust build up on your AC intake vent cover is to regularly replace your air filters. By replacing your air filters at the recommended intervals (typically 90 days), dust doesn’t have a chance to build up to the point of covering your AC intake vents. If there is dust on your AC intake vent, you can simply remove it with a vacuum, duster, or broom.

What is the Difference Between My Home’s AC Intake and Vent?

Technically, both components can be called “vents” because they are both places where air is circulated in your house. The key difference is that your intake vents are “pulling” air from the room and your duct vents are “pushing” conditioned air into the room. You can typically tell the difference visually as intake vents are larger in size and fewer in number than duct vents, which are often found in every room of your house.

Replace Your Air Filters Today

Shop different MERV rated air filters below and make sure your central air system is running smoothly. You can choose your home air filters appropriate size at one of the links below.