Near Minneapolis, the Jones family was having serious comfort issues in their two-story colonial.

Each winter, the upstairs master suite was so cold the owners had to use an electric blanket, while rooms down the hall were too warm. The problem reversed itself in summer, when the master suite overheated and the other bedrooms were too cold. The main level experienced similar issues, with the living room over-conditioned and barely any air reaching the family room.

Comfort problems like these are common in residential HVAC, and can be difficult to diagnose and solve without knowing the airflow of each supply register. Despite challenges of airflow measurement and balancing, this is an essential practice to ensure the long-term comfort and satisfaction of your customers.

The Jones home is an ideal example to demonstrate how residential airflow balancing works, how to overcome challenges and how this practice can benefit your business and customers.


Airflow balancing has typically been limited to commercial HVAC, but there is a growing demand and opportunity to bring this practice to residential HVAC.

At its most basic, airflow balancing involves opening and closing supply register dampers to more evenly condition a home.

Technicians open or close dampers based on how much airflow each register receives and what is needed to condition a room based on its load calculation. The process starts with all dampers fully open to measure how much air each register delivers, then dampers are closed in rooms that are getting too much airflow relative to the required flow. Airflow capture hoods are the recommended tools to gather flow measurements.

There are a number of challenges that greet HVAC technicians who undertake airflow balancing. The cost of equipment is only one part of the equation.

Most hoods are designed for commercial applications with large 24-by-24-inch openings. This presents a key hurdle in residential testing because there is a wide variety of register shapes and sizes that need to be tested, and they are almost always smaller than typical commercial vents.

Accessing these registers is another obstacle, with crown molding, toe-kick and other placements making it difficult to achieve a good seal. Residential registers also have lower airflow than commercial ones, which can be more difficult to measure.

Despite these challenges, there’s an opportunity for residential HVAC companies to set themselves apart in the market by offering airflow balancing. This service can help improve customer satisfaction because new systems deliver air as promised, creating a positive return on investment for your customer and reducing the volume of callbacks for comfort issues.


Comfort issues plagued the Jones family because their home was poorly balanced, even though their furnace and air conditioner were both functioning properly.

The first step in diagnosing the issue from an HVAC perspective was to gather measurements and observations about the 3,100-square-foot home, and test flow at each register.

The basement was mostly finished and conditioned, and the home’s walls and attic were well insulated. The home measured a good air tightness of 2.4 ACH50. Air handler flow measured 536 CFM, and static pressure in the supply plenum was 0.53 in W.C. The furnace was located on the western side of the home’s basement.

With these measurements, it was time to measure the airflow at each register. This offered a way to diagnose issues and improve airflow on a room-by-room basis.

In the Jones home, these tests revealed that airflow was extremely unbalanced both upstairs and downstairs, and room to room. Two registers in the master suite were only measuring a total of 8 cfm, while the bedrooms down the hall measured 114 and 115 each. On the main level, one living room register measured 144 cfm, while the two family room registers measured 10 cfm total. Between upstairs and downstairs, and one side of the house to another, airflow was not sufficiently consistent with the heating and cooling loads. (See Figure 1.)

The source of the extreme imbalance was within the duct system. The main damper was mistakenly closed, meaning most air only reached the one or two registers per floor that branched from the center trunk line before the closed damper, and did not reach other areas of the home.

The damper was opened, which increased air handler flow by 15 percent and reduced static pressure in the supply plenum to one-fifth of its original measurement. This greatly improved the family’s comfort, although they still reported that flow to the rooms was unbalanced.

Additional airflow measurements confirmed the homeowners’ complaint. While airflow via the combined master-bedroom registers had increased from 8 cfm to 42 cfm, the room still felt poorly conditioned compared to the other bedrooms because the airflow was still not sufficient to meet the load. The family room improved from 10 cfm total to 29 cfm, but the living room’s flow was still much higher at 71 cfm. (See Figure 2.)


While opening the damper helped deliver more air more evenly throughout the home, airflow balancing was still needed to improve comfort.

With findings from the second airflow test, the technician began closing dampers in the over-conditioned rooms to make sure each room received the appropriate amount of air. This channeled more air into the under-conditioned rooms. 

Ideally, room-by-room calculations should be done first to find the total airflow, in cfm, required to heat or cool each room. Airflow balancing should then set airflow in each room to match the required cfm. However, many homes have airflow that is so poorly distributed that a load calculation is not even necessary.

It will be obvious to technicians with some experience that a master bedroom almost twice the size of the bedrooms at the end of the hall, with more exterior wall area and larger windows, will need much more airflow to be properly conditioned. In these cases, even a rough guesstimate of the correct airflow can create an enormous improvement in comfort. This was the case with the Jones home.

By adjusting just a few of the dampers, the technician was able to achieve a reasonably well-balanced home. Final testing showed the master bedroom now measures a total 58 cfm, with the other bedrooms at 39 and 38. The living room register that started at 144 cfm is now at 32 cfm, with the family room totaling 37 cfm. The total second floor airflow is 172 cfm, with the main floor at 180 cfm. (See Figure 3.)


Residential airflow balancing is an important practice to ensure homeowner comfort, and can also benefit your business.

When a customer purchases a new furnace, air conditioner or both, they often expect a level of comfort equal to or better than their old system. In the Jones home example, the homeowner had purchased a new furnace but it hadn’t fixed their comfort issues.

Airflow balancing can be a natural next step after installing a new appliance. By testing how much airflow travels to different rooms, you can better deliver on a customer’s expectations. This additional service can also improve overall comfort and decrease the chance of callbacks regarding comfort complaints, helping boost overall customer satisfaction.

Publication date: 10/22/2018

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