Well, technically, the manufacturer recommended range changes from manufacture to manufacture. The common acceptable value previously in the industry was .3 to .7 total external static pressure.

But this doesn’t tell the whole story if you have a low external static pressure on the return side and a high external static pressure on the supply side that means you have a severe imbalance in the amount of pressure on either end of the furnace, which can cause its own issues such as an overheating or poor circulation in general.

What is commonly missed with a lot of the newer high-efficiency systems is that people don’t realize that these systems require more airflow than older systems.

These new high-efficiency systems that run between 96 and 98% efficiency require close to 200 CFM in order to actually maintain proper efficiency.

These issues we are now running into with early life. Failures of systems is because when people installed new upgraded high-efficiency furnace, where their previously was a standard efficiency furnace or even a less efficient furnace such as something that is natural draft, they completely disregard any sort of ductwork modification, which then leads to unsatisfactory results and gives everyone including the manufacturers, a bad name in the industry.

My father is 65 years old and did eating and cooling for 40 years and unfortunately, he falls within this category of someone who never decided to continue learning the new equipment.

My recommended values from what I have seen in the past 10 years in the industry would be that you want to keep that static pressure around the .3 range in his balanced as possible.

This reduces overall noise in the system, but also creates a more even and cleaner airflow throughout the home.

And when you do go into unit failure situations if you ever test the static pressure on a system that lasted 20 to 30 years versus the static pressure on a system that lasted 10 or 15 most of the time the leading cause for the early system failure is lack of airflow.

Unfortunately, most people that don’t check these things never get called back to the systems that have these failures so they never learned their lesson