The Importance of Purging Air from a Hydronic System

Hydronic System Maintenance

Hydronic heating and cooling systems, which use water as a material for heat transfer to regulate air temperature in a building, provide excellent HVAC capabilities for homes and large buildings alike.  Hydronic systems make use of water pipes plus manual or automatic balancing valves, and it’s important to eliminate air from the pipes and valves constantly to keep it working properly.

The principal result of air trapped in the system is a loud and irritating banging noise as the water and air travel through the balancing valves.  Air can also disrupt the heat transfer process, as heat can escape from the water into the trapped air and make the system significantly less efficient.  Oxygen that enters the system via the trapped air can also speed up the corrosion process and rust out the inside of the pipes as well as damaging the seals.  Control valves, which use mechanisms to open the valve automatically to respond to changes in the water system, are also an excellent way to keep an HVAC system air-free without maintenance.

Air should be purged from the system after installation, and if done properly the pipes and balancing valves will remain air-free for years.  To begin, locate the ports on either side of the mid-plate (in the center of the valve).  On a small valve measuring less than 2″, air can be purged using only the upstream port.  A larger valve will require purging from both the upstream and downstream ports.  Pipe and valve manufacturers often provide a variety of products to help remove air.

In a water-loop hydronic system, there are several different ways by which air can become trapped in the system, and these different products may be recommended based on the type of trapped air.  Air may be entrained, or contained in bubbles traveling through the pipes with the water; it could also be dissolved into the water if the temperature and system pressure are right.  Entrained and dissolved air can be drained with tools like an “air scoop.”  Free air also sometimes floats upward to the highest point in the system and becomes trapped.  Free air is easily vented automatically on automatic balancing valves.  If the system begins to make more noise than usual, consider purging excess air to return it to normal functioning.

*This post is courtesy of Flow-Pac LLC. Our sincere gratitude goes out to them. Please contact Mr. HVAC if you would like to be a guest writer.