5 Symptoms of Not Enough Return Air And How To Fix

It’s a beautiful Saturday afternoon in the middle of summer, the perfect opportunity to spend time with family. Or you’ve invited a few friends to come over to watch a game as you take a break from a busy week.

Unfortunately, not everything is going to plan. Although the preparations are moving smoothly, you’ve realized that the home isn’t cool enough. The AC system is running. However, it’s struggling to hit the thermostat setting.

Before you press the panic button, consider that the poor cooling output could result from something as small as a weak airflow. It’s very difficult to achieve optimal cooling if you have weak airflow.

Below, we look at the main symptoms of weak airflow, particularly the signs that your AC unit isn’t getting enough return air. Then we discuss common causes of a weak return air, how to fix the issues, and tips to improve HVAC airflow in your home.

What are the Symptoms of Not Enough AC Airflow?

Your air conditioner will often give you signals whenever there’s poor airflow or low airflow from vents in your house. Some of the telltale signs of not enough return air are;

  1. Your home is experiencing hot and cold spots
  2. Weak HVAC system airflow from the vents
  3. Low air velocity when you put a wet finger close to the vent 
  4. HVAC system not heating or cooling properly
  5. Air pressure imbalance in the home

What is Return Air? 

symptoms of not enough return air

Return air during air conditioning is the stale air re-entering the air conditioning unit for re-cooling. It’s primarily characterized by a high temperature.

Additionally, return air is typically laden with impurities acquired from your home, including dirt, allergens, pet dander, smoke particles, etc.

Don’t confuse it with supply air. Supply air is the cool air coming into your rooms from the HVAC systems.

It’s much cleaner and healthier because the AC air filters remove most of the impurities as return air enters the cooling chambers.

Where are the Return Air Vents Located?

Return air vents are often found on the wall, several inches from the floor, to minimize obstructions from the furniture. Raising it a few feet off the floor also reduces the risk of trapping pebbles, soil, and other dirt particles.

At the other end of the hallway close to your central return, another one is installed. It is referred to as the jumper duct because the air is going to jump from the room to the hall.

However, some people prefer to have it on the floor or the ceiling for various reasons. For instance, floor installations make sense if you have ductwork in the crawlspace because it helps in energy efficiency. Meanwhile, ceiling installations are the most practical solution if your ductwork is located in the attic.

What are the Symptoms of Weak Return Airflow? 

There are several signs of weak return airflow. However, you must be extra keen to avoid confusion as HVAC system issues can be complicated.

We recommend keeping an eye out for the following five signs;

1. Cold and Hot Spots

Cold and hot spots mean that some places within the home are colder than others or warmer than others. For instance, you may notice that the kitchen is warmer than the bedroom of the sitting room is colder than the kitchen.

One of the most common causes of such temperature differences across your home is poor air circulation. Specifically, if the HVAC airflow in one section of the home isn’t returning to the AC at the appropriate rate, you may experience poor cooling in that section.

One of the ways to tell for sure that the cold and hot spots are due to poor airflow is to confirm that regions around the supply vents are cooler and those around the return vents hotter.

2. Weak Airflow at the Return Duct

You can manually feel out the air velocity at the return air ducts to verify that airflow around that area is weak. Two ways to do so are using a piece of paper or a wet finger.

For the piece-of-paper test, tear a small piece of paper and place it over the blocked or leaky ducts. Then observe for several seconds to see what happens. You have sufficient airflow if the piece of paper is pushed against and sticks to the return air grille. However, if it doesn’t stick, then the airflow is weak.

Dip one of your fingers in water for the wet finger test and place the wet finger across the return air grille. You’ll feel a strong cold breeze across the finger if there’s sufficient return airflow. The finger will also likely dry up quickly. Otherwise, you have a reduced airflow.

3. Pressure Imbalance 

Sufficient indoor air quality is often characterized by balanced pressure throughout the home. The pressure indoors should also be the same as outdoor pressure. High and low pressure can draw hot air into or drive cool air out of the house.

Unfortunately, poor HVAC airflow issues can cause high pressure in some rooms and low pressure in other rooms because the air entering the AC isn’t being replaced quickly enough (causing low pressure) or vice versa (causing high pressure).

You can feel the pressure using your ears or purchase a barometer to track pressure levels in your home more accurately. If you discover air pressure buildup in your room, the return air isn’t entering the AC as quickly as necessary.

4. Weak Supply Airflow 

Another symptom of not enough return airflow is a weak supply of air. If there’s very little return air entering the AC, where do you expect the supply air to come from?

There are several ways to tell that your air conditioner has a weak supply of air. One quick method is to place the back of your hand across the supply ducts and feel the velocity of the air coming out. If there’s no strong breeze pushing away your hand, the airflow is weak.

Alternatively, use the paper test again. Hold a small piece of paper across the supply duct and observe what happens. A strong supply airflow will blow away the piece of paper while a decreased airflow won’t.

5. The Air Conditioner is not Blowing Air at All

Finally, you may also have weak return air if the air conditioning unit isn’t blowing out any cool air at the supply vent.

Of course, the absence of supply air can also result from other issues like compressor failure. So, you must be extra careful. However, weak return air can cause no supply of air in two ways.

First, a completely blocked return vent automatically means no supply of air. Secondly, weak return airflow can cause the air conditioners to freeze, thus completely blocking return air from getting to the other size.

It’s easy to determine whether your HVAC systems have supply air. Just place your hand across the vents. You’ll feel nothing if there’s no airflow.

Causes of Low AC Airflow Issues + Solutions 

The following are common causes of low return airflow issues and how to fix them. Note that you may need to call an HVAC professional at some stage.

symptoms of not enough return air

1. Clogged Air Filters

AC filters are located right behind the return vents. Therefore, clogged filters can block return air from entering the AC. The filters can become clogged for many reasons.

For instance, floor-mounted vent filters often collect dust and pebbles as people walk across the vents. Meanwhile, ceiling and wall-mounted vent filters can become clogged due to airborne particles, including smoke and dust.

Solution: Ensure optimal AC maintenance. More importantly, clean or replace the filters at least once every month or sooner.

2. Clogged Outdoor Unit  

The outdoor AC unit can become clogged due to leaves and pebbles from winds and storms. For instance, glass clippings can fly through the fins when mowing your lawn.

Salt deposits from acidic rains are also possible. A blocked outdoor unit can prevent heat removal, thus compromising the rate of return air intake.

Solution: Ensure regular maintenance. Inspect the AC for a few minutes every day to catch blockages early and perform a thorough cleaning every month.

3. Low Refrigerant Levels

The HVAC system tries to regulate airflow into and out of the unit to maximize cooling efficiency. Thus, low AC levels can cause slower return air intake.

Low refrigerant levels often result from air leakage hence reduced cooling creating issues with indoor air quality.

There are two types of refrigerant leaks. The first type is leaks from holes in the refrigerant lines, and the second type is due to loosely tightened joints.

Solution: Make sure you don’t have a leak and whenever you do, ensure to fix it speedily. More importantly, remember that only a licensed HVAC technician is permitted to handle refrigerants.

4. Blocked Ducts

Blocked air ducts can impact both the supply and return air. If the unit cannot release supply air at the desired rate because of blocked ducts, it may not be able to accept return air either.

Air ducts can become partially or completely blocked due to bends in the duct system or the buildup of dirt particles, such as hairs, along with the ductwork.

Solution: Proper maintenance can help prevent duct blockages. Otherwise, you must probe the entire duct length to find and remove the blockage.

5. Blocked or Leaky Vents 

Are your return vents blocked? Perhaps the buildup of dirt, hairs, and pet dander has finally blocked the return air pathways.

Alternatively, are some of the vent pipes leaking? You can say bye to efficient cooling if the vents are blocked or leaking as most of or all the return air won’t reach the AC system in the first place.

Solution: Probe the vent pipes, especially the joints, to ensure no blockage or leaks. Otherwise, call your HVAC technician to unblock it or seal the leaks.

6. Over/Undersized Ducts

You may also experience weak return airflow if your vents are oversized, as oversize vents typically cause low pressure.

Undersized return ducts leading to the HVAC unit and undersized supply ducts leading to uneven room temperatures in your living spaces both decrease the system’s performance, drive up your energy bills and limit your comfort.

Solution: There are two ways to solve undersize/oversized vent issues. First, you can hire an HVAC technician to analyze your vents, uninstall the existing vents, and replace them with the correct-size vents.

Alternatively, remove or add more vents to your rooms. You’ll need the input of an HVAC technician here too.

7. The AC Blower is not Working

The AC blower is directly responsible for generating the motion to draw hot indoor air into the air conditioner. So, there can be no airflow if the fan fails.

Air conditioner fans usually fail for three main reasons – dirt buildup, a faulty/dead motor, or broken blades.

Solution: You can fix the first two with regular maintenance. Make sure to clean the fans at least once every year during the professional tune-up. However, you need to replace the fan in case of the latter two issues. 

8. Others

Finally, you may also experience weak airflow due to the wrong thermostat setting, a faulty thermostat, dirty coils, and a limited supply of air from vents.

Dirty coils cannot release heat and thus interferes with HVAC airflow. For instance, if the thermostat is dead, it won’t request cooling even if your home temperatures rise above 100 degrees.

Meanwhile, a small number of supply vents can limit the amount of air the AC can take in at the return vent.

Solution: We recommend regular maintenance to catch these issues early and annual tune-ups to prevent them in the first place. Also, always work closely with your HVAC services provider.

How to Calculate AC Airflow 

If you wish, you can manually calculate the airflow in your home to determine whether you have adequate airflow.

To calculate the cooling load required to meet your comfort needs you will require the size and layout of your home and the number of windows and doors.

Calculation based on room size

ASHRAE recommends that you replace 0.35 of your room’s air every hour, meaning you should completely change the air in your room every three hours.

So, determine the volume of your home (length x width x height) and divide by your air conditioner’s CFM to determine whether you’re hitting this target.

Calculation based on HVAC capacity

This approach can be especially beneficial when selecting the right-size air handler for your room.

Multiply your AC tonnage (one ton = 12,000 BTU) by 400 (the average output of an HVAC unit) and divide by the square footage of the room to find out if you’re getting the correct CFM AC.

How to Balance HVAC Airflow 

If you determine that your airflow isn’t balanced, you can take steps to put things back in order. Follow the steps below;

  • Keep electronic devices that generate a lot of heat away from your thermostat.
  • Remove any obstructions, including furniture that may restrict airflow across the room.
  • Seal the doors and windows appropriately to prevent drafts and loss of conditioned air.

Tips to Improve HVAC Airflow in your Home 

Alternatively, you can take steps to boost weak return airflow. The following are several ways to boost return airflow;

  1. Clean your filters regularly: Ideally, you want to make it a weekly routine to prevent dirt buildup and ensure maximum airflow.
  2. Replace the filters as the manufacturer recommends: Most manufacturers recommend replacing non-washable filters every month. Using your filters longer can impact airflow.
  3. Inspect the outdoor unit daily to catch obstructions: Leaves, twigs, branches, and grass clippings on the outdoor unit can cause HVAC airflow problems. The good news is, that most causes of these HVAC airflow problems are relatively inexpensive to fix.
  4. Dust the vent grilles regularly: Make it a habit to inspect and clean your vent grilles. Use a soft dry cloth to dust off the area and look through the grilles to see if there are pebbles trapped inside.
  5. Clean the fan blades regularly: Many people forget to clean the blower fans when dusting the air conditioner. Dirt buildup on the fans slows down fan revolution and can easily result in broken blades.
  6. Use indoor fans to help your blower fans: Ceiling fans can help direct stale indoor air into the return vents while distributing conditioned cool air throughout the house. You just need to set the fans correctly.
  7. Schedule annual tuneups: Many homeowners skip annual maintenance due to cost. But, have you ever thought about the alternative? If you don’t schedule an annual tune-up, you’ll likely need even more expensive repairs during the summer season.

Symptoms of Not Enough Return Air FAQs 

What happens if there’s not enough return air?

The air conditioner will not cool properly if there’s not enough return air. Even worse, your air conditioner might become frozen, necessitating expensive repairs or complete replacement.

How do I know if my return air vent is working? 

The easiest way to find out is to place your hand across the return vent grille. You will feel a push and breeze if there’s enough return air. Otherwise, your return airflow is lacking.

Do I need more return air vents? 

If you can have more, please do. Although one return vent per room is often enough, two or three vents in a room generate even better airflow for maximum AC performance.

How big should my return air duct be? 

A typical AC air vent is 4-6 by 10-12 inches. However, some units are larger or smaller, depending on the type of AC. It’s best to work with an HVAC professional to determine the best vent sizes for your home.

Can you have too much return air? 

Yes, you can have too much return air, and the consequences are not good. For instance, you may experience negative pressure in a closed bedroom door if the AC draws too much return air.


Now you know how to spot signs of not enough return air when your AC is running. You also know the most common causes of return air and what to do in each case.

Generally, regular maintenance can save you in many ways. Don’t hesitate to give us a call if you have questions.

Call a technician to balance the HVAC airflow issues by adjusting internal dampers or correcting issues like duct leakage.