As I talk with HVAC professionals who correct airflow problems, they tell me about the many errors they encounter. Even though installation practices vary regionally, there’s a pattern of air upgrade opportunities that consistently repeats. Let’s look at the top five ways progressive contractors are solving airflow issues.

No. 1 — Restrictive Air Filters

The runaway winner: restrictive air filters. There is an epidemic in our industry of contractors trying to cram too much air through a filter that can’t handle it. It’s common to hear stories of 5-ton equipment trying to pull all its return air through a 16-by-25-by-1-inch pleated filter. 

Restrictive filters extend beyond the nasty, plugged up examples many of us find in the field. A filter that is undersized, or installed in a poorly designed rack, can yield the same results. To identify this problem, measure static pressure drop across the filter because a visual inspection just won’t cut it. If filter pressure drop exceeds 20 percent of the equipment’s maximum rated total external static pressure (TESP), there’s a good chance the filter is too restrictive.

Contractors upgrade filtration systems to larger, less restrictive options to capitalize on this opportunity. They ensure that customers who want a pleated filter can own one in a way that won’t sacrifice system performance. Once they upgrade the filter, they retest filter pressure drop to verify it is acceptable.

No. 2 — Poorly Installed Flexible Ducts

Flexible ducts have a bad name among many in the industry — mostly because they are installed incorrectly a majority of the time. Common problems range from improper sizing, poor suspension, and pinched connections.

The most successful contractors use an air-balancing hood to help customers understand delivered airflow. Once mom sees why little Timmy’s room is so hot in the summer and cold in the winter, she has the information necessary to make smart decisions. This simple step establishes trust and keeps the competition away.

Typical solutions to poorly installed flexible ducts include:

  • Adding new ducts to achieve proper airflow;
  • Removing excess core;
  • Adding duct suspension; and
  • Removing pinch points at boots and takeoffs.

To verify the work, contractors should use the balancing hood again after repairs are complete.

No. 3 — Duct Leakage

You would think duct leakage is the No. 1 airflow issue HVAC professionals solve, but it’s not, according to those I talked with. They understand there’s more to a properly operating duct system than duct leakage, and that it should be kept in context. While duct leakage wasn’t the No. 1 opportunity, it is still a significant defect to correct.

Before duct leakage is addressed, most professionals measure TESP before they ever grab a brush and bucket of mastic. They know when TESP is excessive, other issues need to be addressed before duct sealing. It’s a simple go/no-go test that keeps them from creating more problems than they solve.

If the system passes this test, they perform additional diagnostic tests to quantify the amount of duct leakage. Once these tests are complete, sealing begins to contain any lost air. A test out is then performed to show the level of improvement made to the ducts.

No. 4 — Restrictive Indoor Coils

Another high-ranking opportunity is restrictive indoor coils. Whether the coil was plugged with debris or undersized, addressing this defect yields big airflow improvements.

Measuring static pressure drop across the coil when wet identifies this problem. When pressure drop is greater than 2/10-3/10 of an inch of water column (w.c.), the coil is probably restricted and needs a visual inspection. Don’t be surprised if you begin to discover brand-new, clean coils running pressure drops of ½-inch w.c. and higher.

If a visual inspection reveals the coil is dirty, a thorough cleaning is in order. What if the coil is clean? First, you’ll need to determine fan airflow. If it’s excessive, a simple fan speed adjustment may correct the high pressure drop.

A system with proper fan airflow means you need to review the manufacturer’s coil pressure drop tables. Find out what the coil’s design pressure drop should be at proper airflow. If it is excessive, you may need to select a coil with lower pressure drop to effectively handle the right amount of air.

No. 5 — Poor Equipment Connections

It’s tough to get air into a duct system when it can’t get out of the air handling equipment. To solve this problem, many contractors replace restrictive duct fittings near the equipment. The list of these upgrades is extensive, yet they fit into one category. Some of the most common repairs include:

  • Replacing undersized return drops with larger ones that use turning vanes or radius heel elbows;
  • Removing restrictive duct transitions and installing low equivalent length fittings;
  • Installing splitter-tees in place of short supply plenums that cause turbulence and uneven temperatures; and
  • Correcting supply ducts that are too close to the equipment and act as returns.

These opportunities use a combination of old-fashioned common sense as well as static pressure, velocity, airflow, and temperature measurements. With a little training, you can look at a duct fitting and see potential problems. Measurements back up this assumption and provide additional diagnostic clues.

To make these measurements and repairs easier to do, National Comfort Institute (NCI) has tables that include common static pressure, airflow, and temperature tests with their corresponding repairs. Send me an email at the address at the top of the page, and I would be glad to share them with you.

How to Capitalize on the Inventory

Additional opportunities include the “Bermuda Triangle of Airflow” — what we refer to as duct board junction boxes, structural restrictions, too many elbows, and the list goes on.

When you know how to address them, you can convert all the old school assumptions, rules of thumb, and poor craftsmanship that have plagued our industry for decades into a substantial source of income. The contractors I talked with have mastered these principles and measure systems to discover opportunities that aren’t seasonally driven.

If you’re tired of waiting for hot and cold weather to keep you busy, look for the needed changes that are right in front of you. When you assume the systems you maintain, service, and install are working as intended, you could be missing a chance to improve them and deliver a superior product. Learn to optimize duct systems, and perform installations that deliver what you promise.  

If you’re an HVAC contractor or technician interested in learning more about air upgrade opportunities, contact David at or call him at 800-633-7058. NCI’s website is full of free technical articles and downloads to help you improve your professionalism and strengthen your company.