HVAC Air Balancing: What You Should Know

Floor air vent that matches the color of the floor.
Nat Rea

If you’re struggling with maintaining—or even attaining—a consistent temperature throughout your house, your HVAC system may be out of balance. This guide will explain the basics of air balancing, including how DIYers can tackle the job and when they should call a professional to sort out their home’s heating and air conditioning system.

Some homeowners know the struggle of trying to achieve home temperature homeostasis, which is a made-up term to perfectly describe the whole home being the same temperature. When the system isn’t running correctly, it’s common to have that one room that never seems to warm up or the upstairs getting uncomfortably hot every time the first floor reaches the ideal temperature. For folks with forced hot air and central AC systems, there’s a good chance that they have air balancing problems.

But what is air balancing, and how does it work? This guide will explain all the basics. Keep reading to learn more.

What is Air Balancing?

Air balancing is fine-tuning a home’s forced hot air or air conditioning system to distribute conditioned air evenly. Air balancing involves dialing in each duct or vent in the house so that the entire home reaches the same temperature simultaneously. Techs and DIYers will close the vents or dampers heading to some rooms while opening some in other rooms.

Installers air-balance HVAC systems when they install them, jockeying the amount of airflow going to each room until the temperatures are consistent in the space. However, a system can fall out of balance. This can happen for many reasons:

  • Someone may have tweaked the dampers or vents
  • An addition project may make a room or wing of the home larger
  • Interior walls installed after construction may block airflow
  • Insulation may be damaged in certain areas of the home
  • More efficient windows and doors could change airflow needs

Even the addition or removal of furniture can change how much airflow a room needs and how quickly it heats up. If any of these conditions exist, some rooms may feel warmer or colder sooner than others. Some rooms may not reach their ideal temperatures at all.

How To Tell if Your System is Out of Balance

It’s fairly easy to tell if an HVAC system is out of balance. Generally speaking, significant temperature changes from room to room or floor to floor would indicate that these spaces are receiving inappropriate amounts of conditioned air. Some spaces might be receiving too much airflow and preventing the other rooms from getting enough. Conversely, some rooms may have closed dampers, forcing the air to escape the system in another room.

Some indicators that you may need to have an HVAC system air-balanced include:

  • Temperature changes of more than 2 or 3 degrees from room to room or floor to floor
  • Inefficient use of the HVAC system leads to higher energy bills (for example, having to crank the living room thermostat just to warm the bedroom slightly)
  • Vents that don’t receive airflow despite having open dampers
  • Vents that seem to get too much airflow or make a slight whistling sound when partially closed

If these conditions exist, the system is probably out of balance.

How to DIY Air Balancing

While the causes and conditions of an out-of-balance system are various, most DIYers can improve the comfort of their home on their own. All they need is a bit of information and patience.

Air Balancing Fixtures

First, there are two mechanisms that can help a DIYer balance airflow: dampers and vents. They’re both adjustable but it’s helpful to know the difference.

  • Dampers are valve-like fixtures installed in the branches of an HVAC system. They have handles that protrude out of the ductwork, allowing users to adjust how open or closed they are. When the handle is parallel to the duct, the damper is wide open. When the damper is perpendicular to the duct, it’s closed. They can also be adjusted anywhere in the middle for optimal airflow.
  • Vents are installed at the end of the HVAC branches, usually fixed to walls or floors. They have adjustable louvers built in, and users can adjust them with the knob or handle on the unit. In most cases, the knob or handle pushed in one direction will open the louvers all the way, while the other direction closes them. The settings in the middle will dial the airflow in.

Note: Some vents do not have louvers. These are usually return vents, which pull the air from the room and cycle it back through the HVAC system, heating or cooling it again before pumping it back into the home. If there is air coming out of a louver-less vent, homeowners should consider replacing the vent with a louvered model.

How To Adjust Airflow

A DIYer might not be able to get their home perfectly in tune, but they can certainly improve the comfort level of their home. Part of this is essentially acting as an HVAC Goldilocks, moving from room to room until everything feels just right.

1. Locate the furnace or air conditioner and track the ductwork system. Take note of any dampers along the way, as well as the direction of the ducts. The first vents on the system are typically the ones with the most airflow, while those on the end of the system may be starving for airflow.

2. Activate the unit’s fan by switching it to the on position at the thermostat. Walk from room to room, first writing down the number of vents in the room, then noting the airflow at each vent. Write down what the airflow feels like, using the labels high, medium, and low. For simplicity’s sake, let’s consider medium airflow to be ideal.

Tip: For a more objective way to judge airflow: Place a piece of paper over the vent, holding the paper’s top edge on the top of the vent and letting the bottom of the paper float. Take note of how far the paper blows from the wall. This isn’t an exact science, but it’s a helpful gauge.

3. Open the dampers or louvers in rooms with lower airflow first. Some of these vents may have been closed, and this alone could bring the system closer to balance. Next, investigate the other rooms and assess their airflow.

4. Check the vents in rooms that originally had medium airflow. More than likely, their airflow will feel like it dropped quite a bit. Open the dampers or louvers in these rooms slightly until they receive medium airflow, similar to the rooms you’ve already adjusted. Check all the vents again to get an idea of their progress.

5. The vents that originally were receiving high airflow will probably feel much more reasonable now. However, if they’re still receiving too much air, dial back their louvers or dampers a bit. This will divert airflow to the vents you’ve already adjusted, balancing the system.

6. Set the HVAC system back to the normal setting and allow it to heat or cool the home over the next few days. Take note of the comfort level throughout the home during the day and at night and adjust the vents as necessary.

Note: This is a helpful way to bring a home closer to balance, but it’s not perfect. Large rooms require a higher volume of airflow than small rooms, so dialing them back to roughly the same CFM (cubic feet per minute, which we’ve indicated with our paper airflow test) will mean that these two rooms aren’t receiving the correct amount of airflow for their size. This means that you’ll need to have a little patience as you make some necessary adjustments over the course of several weeks.

When You Should Call a Pro for Air Balancing

Most DIYers can improve the comfort of their home with some simple adjustments to the vents and dampers. However, in cases where those adjustments don’t make a difference or provide consistent results, it may be time to call a professional.

When a professional HVAC technician air balances a system, they take specific measurements at each vent to diagnose potential issues. They’ll also look at the unit’s fan speed, dampers, and even ductwork size. For instance, large rooms may require more air volume, which could mean installing a larger vent and new, larger ductwork. Rooms on the end of the line may require more air pressure for conditioned air to reach them, resulting in smaller ductwork.

Generally speaking, HVAC companies will charge around $100 per opening or vent. This can get pricey quickly, but the result will be an air-balanced system that distributes the right amount of air to each room for a consistent temperature throughout the home.


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