What is Duct Static Pressure in HVAC?

Duct Static Pressure - What Is It?

Duct static pressure is a crucial but underrated concept in the heating and cooling world. Generally speaking, the term refers to the resistance of airflow through an HVAC system. This controls the speed at which the air travels through the ducts to the rooms of the building, which can have a major impact on the system's heating and cooling capacity. At the most basic level, your HVAC equipment must produce more pressure than the static value in the ducts, or it won't be able to force air through the ductwork.

Why is Duct Static Pressure Important in HVAC?

Getting your duct static pressure right is an absolutely vital part of a properly functioning, efficient HVAC system. Incorrect static pressure can cause significant potential issues like annoying, extra-noisy systems and causing your HVAC units to run for longer than expected. This means higher energy bills and extra stress on your equipment, causing it to fail faster.

Issues with duct static pressure can also lead to air quality and temperature issues in certain parts of your space because of uneven air flow. This is especially important in commercial buildings or schools, where top air quality is critical for health and safety reasons.

What is Used to Measure Duct Static Pressure?

The most common way to measure duct static pressure is through the use of pressure sensors. They offer convenience and constant monitoring through special pressure sensing technology, which is a necessary feature for large systems or ones that heat or cool important places. In addition, some HVAC systems will use a manometer to measure pressure, a type of fluid pressure sensor. In many cases, the average duct static pressure will be around 0.5 inches, though this will vary depending on the specifics of the system.

What Causes High Static Pressure?

High duct static pressure can cause serious issues for your HVAC system and can stem from a variety of causes. Some of the most common are linked to the installation of the system, either from poor workmanship or improper duct and system sizing. In other cases, using the wrong air filter or allowing a clogged filter to remain in use will cause higher-than-expected static pressure in your ducts. Finally, minor issues like a kink in flexible ducts can restrict or modify airflow, increasing static pressure.

How to Fix High Static Pressure

The ways to fix high pressure are as diverse as the causes. Sometimes, it'll be as simple as changing out your air filter. However, in the most serious situations, you may need to modify ductwork or even replace and reinstall the whole system.

What Causes Low Static Pressure?

Problems with duct static pressure go both ways. While low pressure is less common, it's still possible and worth understanding. It's typically caused by overly large ducts relative to your heating and cooling equipment or leaking ductwork or plenums. Low pressure may also stem from missing filters, low fan speed, separate duct connections, or other minor issues. In situations where major energy-efficient upgrades have been made to a house or building, old ducts may also not be compatible with new HVAC and energy systems.

How to Fix Low Static Pressure

Fixing low duct static pressure can be accomplished in a few different ways. If a duct is too big, you can taper it to increase air velocity. You can also add a return air duct or increase the return air trunk or airdrop. Finally, check your fan speed to ensure it's spinning correctly.

Know Your Duct Static Pressure To Avoid HVAC Issues

Unfortunately, most home and building owners have no idea what's going on in their ducts. While it may feel simpler just to continue ignoring it as long as there aren't any problems, this is a recipe for potentially serious, long-term issues. The solution is adding environmental sensors or including them as part of your next HVAC upgrade. These devices put information on your building and system right at your fingertips whenever needed. Check out the wide variety of Veris pressure sensors today to find the one that's right for your HVAC needs.