Duct Installation and Testing

How air diagnostics lead to better-functioning HVAC systems and happier customers
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Provided by The Air Conditioning, Heating and Refrigeration NEWS

Learning Objectives:

  1. Explain the steps required to measure static pressure.
  2. Discuss the most common duct problems, how to diagnose them, and how they can be resolved.
  3. List what tools are needed for measuring total external static pressure (TESP).
  4. Describe how to integrate air diagnostics into a company’s daily operation.


1 AIA LU/Elective
1 PDH*
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Purpose statement:

This course will examine how air diagnostics lead to better-functioning HVAC systems and happier customers.

When Bad Ducts Meet Great Equipment

Every industry has its problems and the HVAC business is no different. One of the most common issues that gives our trade a black eye are well-meaning contractors hooking up high-efficiency equipment to substandard duct systems. When this unfortunate combination occurs, you, your company, your customers, the distributor, and the equipment manufacturer all suffer the consequences.

Let’s look at how our industry got into the mess of great equipment installed on not-so-great duct systems and one way you can prevent it.

Photo courtesy of David Richardson

EFFICIENCY: The typical HVAC system installed across the United States operates at 57% of the equipment’s laboratory-rated efficiency. Are you inheriting another contractor’s poor duct installation?

Results of a Typical Installation

For decades, NCI (National Comfort Institute Inc.) studies have shown the typical installed HVAC system in the United States operates at about 57% of the equipment’s laboratory-rated efficiency. The two biggest factors contributing to this low percentage are excessive static pressure and low airflow.

On average, the operating TESP (Total External Static Pressure) of most air handling equipment is 160% of manufacturer recommendations. This results in low fan airflow on PSC (permanent split capacitor) blowers and excessive watt draw on ECM (electronically commutated motor) blowers.

Equipment only operates as well as the duct system you attach it to. Some common problems encountered from selling and installing high-efficiency equipment on substandard duct systems are:

  • Continuous equipment problems;
  • Premature component failures, such as motors, compressors, and heat exchangers;
  • Frequent callbacks;
  • Poor brand reputation for the contractor, distributor, and equipment manufacturer;
  • Negative online reviews and excessive complaints; and
  • Frustration, excuses, and finger-pointing.

When contractors with good intentions realize bad ducts are the source of many of their troubles, they ask themselves what they need to do next. But first, it helps to look at how we got here, so we don’t repeat the same mistakes.

Assume — Misdiagnose — Guess

There’s a three-step process handed down from generation to generation. We’ve probably all done it at some point, and when we recognize it, we get uncomfortable.

Many in our industry unknowingly choose to assume, misdiagnose, and guess when they replace equipment. They use this trio, hoping their recommendations will work on the existing duct system. This usually happens because they don’t know there’s a better way.

This approach often involves the technician diagnosing conditions that warrant equipment replacement. Then, the salesperson comes out to record the existing equipment model numbers and what it will take to hook up the new equipment. It’s a quick way to move from call to call but leaves a lot of important information out. The customer receives cookie cutter recommendations for good, better, or best options based on limited information.

Once the customer makes their decision and the job is sold, it’s up to the installers to improvise and adapt to the field conditions. This is where the job gets worse. The install team must make use of the materials at their disposal, and it’s rarely what they need. So, they improvise to get the equipment running. The question is, how well will that equipment work — and for how long?

Companies who guess make a lot of assumptions. They often turn the new equipment on, believing it is factory set. Then they walk away from the job, only to wonder why their customers call back with complaints. I think we can all agree that callbacks are not an effective form of quality control.

Ask yourself whether your technicians spend a lot of their time going back and correcting issues that a proper startup could easily fix? If so, there’s a break in the chain at your company. The good news is that there is a better way. One that won’t result in the headaches and frustrations that so many of us have experienced.

Test — Diagnose — Repair

Another approach is to test, diagnose, and repair. Only the best in our industry will follow it. They use this trio, knowing their recommendations will work. They also discover whether the existing duct system is in good condition or if it needs additional repairs so the new equipment can operate as designed.

This method offers a quick, proactive duct system evaluation instead of solving issues reactively once the equipment is up and running. Your technicians are usually the ones who find the issues before your company inherits them by first gathering test data.

In less than five minutes, they can install test ports in the duct system/equipment, measure four static pressure readings, and interpret fan airflow. From this information, the technician can identify duct system restrictions, improperly sized filters, restrictive coils, and airflow issues.

Next, the technician hands off their findings to a salesperson who addresses and offers solutions to the customer. Once they know the duct system condition, they prepare a scope of work based on the measurements or offer further airflow diagnostic testing.

After the install team completes the new equipment replacement, a startup tech (or the install team) performs another series of the same tests. They assure the system works as designed and that they left no issues that could lead to problems down the road.

How peaceful would it be to have the confidence to know that if there’s a callback, it isn’t the duct system or an installation issue? That’s one major benefit measuring brings to your company.

Sales Determines the First Step

You may have noticed that both approaches discussed rely heavily on the salesperson. They have a lot of responsibility for inheriting a bad duct system.

One method relies on guessing, the other on measurement. However, just because your technicians measure, it doesn’t mean their readings will be used. That is the salesperson’s responsibility. Ignoring the test results is worse than guessing!

If a salesperson takes their first step in the wrong direction, everyone else will follow and suffer from the decision. They choose to assume-misdiagnose-guess or test-diagnose-repair. When given a choice, most salespeople will make the right decision. Unfortunately, many don’t even know the second option exists.

However, once they’re aware, another problem surfaces. How do you handle a sales call where there isn’t a technician involved? Many salespeople don’t know how to test. This single issue will stop most in their tracks. How can you overcome this obstacle and assure your salespeople don’t recommend and sell equipment that won’t work on a duct system that needs upgrades?

Unfortunately, some will keep doing things the easy way. They won’t change even if there’s a better way. But, if you’re tired of the insanity and want to prevent these issues, there is a way to succeed. Again, it depends on the willingness and ability of your salespeople. Here are two options to consider. I bet you can come up with additional possibilities.

The Tag Team – Have an available technician who knows how to test and diagnose airflow issues pair up with your salesperson. The technician gathers the readings and translates them for the salesperson. The salesperson then shares the results with the customer in a way that makes sense and is easy to understand.

The Former Tech – Some of the best salespeople I know are former technicians. If you’re fortunate enough to have one, encourage them to test for airside issues. Then, equip them with the tools and test instruments they need to discover hidden duct system problems.

Next Steps

An old healthcare motto is “Prescription without diagnosis is malpractice.” The same holds true with replacement HVAC equipment. If you leave out the testing and recommend new equipment, you’re guilty of malpractice. You prescribed without a diagnosis.

Many of the things I’ve talked about introduce a salesperson to a new mindset and skillset. If they’re having success moving a lot of equipment, you’ll have a hard time getting them to change their ways. However, if they’re skipping necessary steps and inadvertently creating extra work and callbacks for everyone else, it’s time for a change.

It’s important to understand that once new equipment is installed and running, proper startup relies on the commissioning tech or installer to assure everything is right. But, if the salesperson sold something that can’t be set up correctly, they unintentionally set up your entire company for failure. Ultimately, you must deal with it. There’s never an easy or cheap way to clean up a new equipment mess, so why not commit to being proactive instead of reactive?

David Richardson, serves the HVAC industry as a curriculum developer and trainer at National Comfort Institute, Inc. (NCI). NCI specializes in training that focuses on improving, measuring, and verifying HVAC and Building Performance.


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Originally published in February 2023