Why Does My Central Air Have Two Filters?

The time has come for you to change your HVAC system’s air filter; you start looking for the slots and discover two of those. This fact might leave you wondering ‘why does my central air have two filters?’.

The majority of central air units would actually have two filters – you’ll find one in the air handler and another one (or even a few) in the return vents. The households that have a furnace would also have a filter in the blower compartment.

Do All Central AC Have Filters?

Yes, all heating and cooling systems should have at least one air filter. Some systems might have more than one.

If you can’t find the filter in the unit, then the chances are high that you’re looking in the wrong place.

  • If you have a vertical air handler with a return duct located on the top, then the filter slot should be right above the unit. If the return air duct is located at the bottom of the air handler, then the slot is below the unit.
  • If you have a horizontal unit and the return duct is located on the side of the air handler, then the filter slot is on the same side as the return air duct.
  • For any other system, the filters are usually installed right behind the return grill (you can have those on your walls or ceiling). Old houses can have return air grilles on the floor.

Read: Ductless Vs Central Air System – What Is More Efficient?

Do AC Units Have 2 Filters?

A lot of central air units have at least two filters, though you can find systems that have only one.

The reason why there are a couple of filters is because not only the air that is traveling into the air handler needs to be filtered, but also the air passing through the return vents.

How Many Filters Does a Heat Pump Have?

Heat pumps have two types of filters – permanent and temporary ones. Only the latter need to be replaced from time to time. 

If your system has an air handler, then the first filter is located at the intake side of the unit.

The rest of the filters can be found in the return air vent. Normally, it is located close to the thermostat, either on the wall, ceiling, or floor.

Tip: the return air vents are bigger than the supply vents. It is easy to identify the return air vent when the heat pump is on, simply place a piece of toilet paper near the vent – the return air will suck the tissue in.

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Read: Ceiling Vents Vs. Floor Vents. What’s The Difference And Efficiency?

How Many HVAC Filters Do I Have?

Any system has at least one air filter. However, you might want to double-check your unit to find out for sure how many filters your system has.

The first one is usually located on the air handler. The air handler is a large metal box – you should look for something that looks like a removable cover (that’s the filter slot).

After that, you should find any return vents – they are, in general, either rectangular or square and bigger than the rest of the vents.

Once you have found the return vents, remove the covers to make sure that there is an old filter inside. 

Does My Furnace Have Two Filters?

In the majority of cases, your furnace’s air filter would be located in the blower. Whether you would have to open the side, top, or bottom door will depend on the type of the unit.

If you have a vertical heating unit and the airflow is traveling downwards, then you’ll have to find the blower compartment and open the top door to get to the filter. Do bear in mind that such a type might require two filters.

Fact: if you have separate heating and cooling systems, then your air conditioner and furnace might have different filters.

Read: Does HVAC Purify Air?

Why Does My Furnace Have Two Filter Slots?

This could be because…

  • Your house has multiple return vents
  • The system has an air handler (in case you have a heat pump) and a return vent
  • You have two separate heating systems

Can I Stack Two 1 Inch Air Filters?

You should never stack air filters.

Even though you might think that the air would get cleaned a bit better if you have two filters side by side that is not exactly the case.

It would become a lot harder for the HVAC system to suck in enough air. This will result in higher utility bills and a less efficient heating and cooling system.

Stacking two filters will also make your system overwork which will cause long-term damage to its components.

If you feel like a single 1-inch filter isn’t doing a great job at filtering out the particles from the air, then upgrade to a thicker option, if the filter slot allows that.

Make sure that the chosen air filter fits the slot. A ‘wobbly’ filter will fail to effectively filter the air.

Read: How Strong Should Air Come Out Of Vents?

Do I Need Both a Furnace Filter and a Return Air Grill Filter?

Yes, you are going to need a furnace filter and a return duct filter.

The main purpose of the furnace filter is to protect the blower from dust, debris, pet dander, and so on. 

Return vent filters are recommended as they not only protect the HVAC equipment but also make the air that you breathe cleaner by filtering out various particulates. 

Is the Return Filter the Same as the Furnace Filter?

FeatureReturn Air FilterFurnace Filter
LocationBehind the air return ventIn the furnace’s blower compartment
FunctionProtects the equipment Helps the system run efficiently Clears the airProtects the furnace equipment Helps the heating system run efficiently Clears the air
Filtration LevelReturn air filters usually have a MERV rating between 8 and 13Furnace filters usually have a MERV rating between 4 and 12
LifespanIn general,1-3 monthsFrom 1 to 12 months
CostFrom about $5 to $50 per filterBetween around $15 and $25 per filter

How Do I Check My Furnace Filter?

You can check your furnace filter every month or so to make sure that it is not clogged.

To locate the furnace filter, find the large metal compartment next to the blower. The filter slot will be either on the side of the compartment’s door or at the bottom.

  • In a horizontal unit, the filter can be found on the intake side.
  • In a vertical unit, the filter will be in the bottom door (as the air is moving upwards). In such a case, you would have to open both the top and the bottom door. 
  • In a vertical unit where the air is moving downwards, you would have to open the top door to check the filter.

What Happens If You Use AC Without Filter?

The air in your house will become dustier if your system doesn’t have a filter. When it comes to the actual AC unit, the evaporator coil will eventually get clogged with debris, dust, and hair. The component won’t be able to cool the air as efficiently; in fact, the AC might stop cooling at all in a few months.

Read: Do Vent Deflectors Really Work?