I made a comment about pairing larger-tonnage fans with smaller-tonnage outdoor units that has drawn a lot of interest.

What if there were a quick and simple way to anticipate what would happen to static pressures if you increased or decreased airflow?

For decades, many company business models have remained the same. Run service calls one after the other, and fix or replace the equipment. This often results in companies barely surviving and a bleak outlook on the future.

There is a formula that successful contractors use to answer such questions and generate customer interest in duct upgrades. Their approach focuses on the facts about what an HVAC system is doing — they don’t share opinions or use smoke and mirrors.

The good news is that once you measure static pressure, you can estimate fan airflow in less than 30 seconds with the right information. Once technicians understand that static pressure testing gets them to fan airflow, they will see why it is important to measure it on every call.

You might wonder, “Why can’t I just use a duct calculator and tape measure to identify duct repairs?” You could, but that means making a lot of assumptions and wasting valuable time.

Airflow is a general term that’s easy to misinterpret. When I first learned about airflow, I had to classify it into four values that made sense to me. The easiest options are the measurement location or source of the airflow reading.

Many of the calls I receive about goofy static pressure readings typically tie into one of five issues. Let’s look at these issues and how you can be sure they don’t affect your measurements.

The first reason not to measure static pressure is because hooking up a refrigeration manifold to the system tells you everything you need to know. Don’t worry about the fact that this practice often leads to leaks, can introduce non-condensables, and can cause potential refrigerant contamination.

In order to understand the foundational principles of duct sizing, a thorough study of ACCA Manual D is a great place to start.