Implementing company-wide static pressure measurements can be tough. Consistency is one of the biggest challenges to overcome. At National Comfort Institute Inc. (NCI), we recommend measuring static pressure on every call, just like a medical professional measures blood pressure. However, that’s hard to do when you’re struggling to keep up with demand during extreme weather.

Many companies take an all-or-nothing approach. If there aren’t many calls, the techs measure static pressure every time. But when business picks up, they don’t take any pressure measurements because they’re too busy. It’s a vicious cycle that leaves a technician questioning the value of static pressure measurement because of the inconsistency. They assume that if it isn’t important enough to do on every call, it must not matter much.

If this problem sounds familiar, you aren’t alone. It’s a common struggle. The good news is there is a solution. The answer is a prompt to help a technician know when to measure based on the symptoms of a service call. This prompt is known as a red flag. Let’s look at how you can use red flags to improve your static pressure measurement consistency and reduce callbacks.


What is a Red Flag?

Traditionally, a red flag is a signal or indicator to warn of impending danger, trouble, or a problem. There is a considerable risk that comes with ignoring red flags that could cause injury or death.

The red flag dates back to the 18th century and has its origin in military communication and symbolism. Today, many of us use red flags in our inboxes to mark important emails that we don’t want to forget.

Bullfighters use a red flag to attract the attention of a bull and draw them in. It’s assumed that bulls don’t like the color red or the waving of the flag. But if you see a red flag, you’ll be grateful to recognize the opportunity to better serve your customers and solve their long-standing problems.

Red flags on a service call identify the need to measure static pressure. It’s often something airflow-related that’s causing the red flag to wave. They’re often repeating problems with an unhappy customer, long-standing equipment issues, or failure. Some common red flags are:

  • Continuous equipment problems
  • Equipment can’t maintain comfortable conditions
  • Compressor failure
  • Cracked heat exchanger
  • Low/no superheat (cooling mode)
  • High head pressure (heat pump-heating mode)
  • Excessive temperature rise (heating mode)
  • Excessive temperature drop (cooling mode)
  • ECM (electronically commutated motor) hunting and failure
  • Furnace cycling on high limit
  • Erratic TXV (thermostatic expansion valve) operation
  • Indoor coil refrigerant leaks
  • An air handler or package unit that won’t drain correctly
  • Condensate blow-off
  • Tin-canning of ductwork when the blower comes on.

These are just a few issues that should draw your attention. They are frequently based on the reason for the service call, customer concerns, or your measurements and observations. After you think about it, I bet you can add a lot of examples to this list. I encourage you to capture them and build a personalized red flag list to share with your team.


Find the Red Flag Cause

Many technicians grab their refrigeration gauges once they arrive at a call, but that might not be the best first step. Instead, start with a visual inspection and look for obvious issues that are easy to overlook. If you don’t spot anything that stands out, then it’s time to measure Total External Static Pressure (TESP).

The following testing steps are generic, so be sure to adapt them to your installation configuration. There are minor differences that depend on whether you’re testing a gas furnace, air handler, or package unit. For more information, email me for a static pressure quick start guide with test location diagrams.

  1. Install a 3/8-inch test port into the duct or equipment where air enters the air-moving equipment. Inspect before you drill — you don’t want to puncture a coil or drain pan. This pressure reading should be taken after the air filter.
  2. Install a 3/8-inch test port into the duct or equipment where air leaves the air-moving equipment.
  3. Turn on your digital manometer or Bluetooth probes. If using Bluetooth probes, also turn on the accompanying smartphone app.
  4. Attach a hose to each pressure tap of the manometer and insert a static pressure tip into the opposite end of each of the hoses.
  5. Insert the static pressure tip (the one attached to the hose going to the (+) port (if equipped) of the manometer) into the 3/8-inch port you installed where air leaves the equipment.
  6. Insert the static pressure tip (the one attached to the hose going to the (-) port (if equipped) of the manometer) into the 3/8-inch port you installed where air enters the equipment.
  7. The measured TESP reading will appear on the manometer display or smartphone app.

Compare the measured TESP against the maximum rated TESP found on the data plate of the air-moving equipment. Ideally, the measured TESP should not exceed the maximum-rated TESP of the air-moving equipment.

The maximum-rated TESP of most residential air-moving equipment is .50” w.c. (inches of water column). If the measured TESP reading exceeds the data plate rating, you probably have an airflow problem. Most equipment can’t move proper airflow when the blower tries to work against excessive pressure.

While high TESP indicates an issue, it doesn’t identify the cause. So, to pinpoint the source, you’ll need a few more readings. Measure duct pressures, pressure drops, and plot fan airflow to get a better view of the airside. Wherever you measure the highest pressures reveals the most restrictive places for airflow to move through the system.


Keep the Red Flag in Context

The goal of the red flag approach is progress over perfection. When we get wrapped up in perfection, it leaves us with only two options — do everything or do nothing. Focusing on progress allows you to consider each service call as they come in. Remember, you’re learning a different approach to measuring static pressure than what you’re currently doing. Expect some bumps along the road.

It’s important to understand that red flag calls are reactive. There is already a problem that you’re trying to solve. The customer is probably frustrated, doubtful, or on edge. Don’t put a lot of pressure on a technician who is dealing with an upset customer AND trying to measure static pressure to identify the problem. Give them the time they need to succeed.

If you do it right, your static pressure testing approach should eventually become proactive. The goal is to discover issues before they become red flags. Then you can inform the customer of your findings before any negative emotions enter the conversation.

Measuring static pressure often points you in the right direction and causes you to look at areas that are easily overlooked. If the air-moving equipment’s TESP is acceptable and moving the right airflow, you just eliminated a potential suspect in your diagnosis. No more guessing.

Some red flag issues are beyond the scope of an HVAC technician and will need to involve a comfort advisor or salesperson. The equipment could be oversized, or they may need major duct upgrades to correct the problem. Make sure you have a way to hand off the red flag, otherwise it could remain unresolved. If the red flag is beyond your company’s skill level, you may need to involve other specialized trades.

You ultimately decide how to handle the red flags you encounter. If you’re content randomly replacing components, equipment, or adjusting refrigerant charge with no success, keep ignoring the red flags. But if you’re tired of callbacks and frustrated customers, try measuring static pressure. I believe the results will surprise you.