Hooked on Hydronics Blog

Why Air Must Be Removed from Hydronic HVAC Systems

Posted by Joe Britt, PE on Dec 1, 2015 11:32:16 AM

TACO 4900 Series Air SeparatorIn hydronic HVAC systems, water is circulated through the pipes and equipment as it delivers and removes energy throughout the system. In a closed loop piping system, the water is kept under pressure and never exposed to the open atmosphere as it travels from the pump discharge back to the suction. And, in this type of closed system, air poses several problems, including:

  • Air Lock – preventing water flow through sections of the piping system
  • Corrosion – of the cast iron and steel pipe, fittings, and equipment
  • Heat Transfer Degradation – as the concentration of dissolved air goes up, the heat capacity of the water goes down

Air may be left in the piping after initial system fill, but the installing contractor typically purges that from the high points in the system. However, dissolved air is carried into the piping system anytime fresh water from the municipality is introduced, such as during initial fill, leaks, or routine maintenance. This is why in closed loop hydronic HVAC systems, air must be properly purged from the piping during initial system fill and during operation.

Free air may be vented out of the high points in the piping system, but dissolved air must be separated from the water by an air separator device. While there may be debate on the merits of inline or tangential air separator configurations, ALL air separators accomplish their tasks by filling the following requirements:

  • Must slow the water and agitate (or change directions)
  • Must be located at or near the warmest part of the piping system
  • Must be located at or near the lowest pressure point in the piping system

Meet these requirements, and the dissolved air will separate from the water where it may be vented (air separation system) or directed to a plain steel expansion tank (air control system).

If air separation effectiveness is important for your application, work with your manufacturer's representative to determine what equipment you need.


Questions? Contact HTS Sales Engineers

Topics: Pumps, Design Engineer Tips

Why we blog

At Heat Transfer Sales of the Carolinas, we are invested in the success of our customers.  And we believe in the products we represent.  We use our blog posts to educate and answer questions about hydronic HVAC and engineered plumbing equipment and the industry in general. 

We are dedicated to:

  • Helping our customers find solutions
  • Innovative thinking
  • Serving as true partners in the HVAC & plumbing industry
  • Representing the latest high-performing equipment

Subscribe to Blog

Recent Posts