Automatic Air Vents
The automatic air vent is found in the piping system of water loops. If air is introduced into the water loop system it eventually finds its way to the automatic air vent where it is vented. The automatic air vents are located throughout the system. Automatic air vents may also be found throughout any hydronic loop system. A hydronic loop is a water loop.

These water loops can be for hot water or chilled water. Any hydronic loop needs an air management system or automatic air bleeder system to keep the air out of the system otherwise, the air will be up in the system and air will block or prevent the flow of water throughout the loop. Water naturally has air in it. Air vents help the water loop by:

Automatic Air Vents

  • Automatic Air Vents keep air out of the loop (hot water or chilled water) by automatically purging the air through a float-type vent.
  • Prevents hydronic airlock.

​Automatic Air Vents | HVAC Hydronics

Tiny microscopic bubbles in the water are eventually released from the water as it is heated and cooled. Furthermore, the air moves throughout the hydronic loop. The air ends up in the risers and the high points in the loop. This air needs to be released from the system otherwise, it will stop the flow of water through the hydronic air block. When the air finds its way to the vent it builds up in the top of the air vent. The air causes the water level inside the vent to decrease and float inside the air vent to drop. When the float drops the air is released from the system through the top of the vent.

As the air escapes the float rises again and seals off the top of the automatic air bleeder preventing water from escaping. As time goes on corrosion and minerals foul the seal at the top of the float in the automatic air vent. The air bleeder pictured has a fouled seal and allows water to escape as well as air. Furthermore, the air bleeders are non-serviceable and need to be replaced when they start leaking water. In some systems, there are manual air bleeders that need to be manually vented from time to time to release any air which may build up.

Automatic Air Vents Maintenance Tip:

  • overtime trash will build up inside the automatic air bleeder and it is difficult to remove. Therefore, the automatic vent will begin leaking from the vent. This means the rubber seal inside the vent either has trash in it. It could also be plugged with calcified minerals from the water. A friend of mine who is the maintenance manager of a large campus keeps spare automatic air vents. When one starts leaking he will replace one with a spare. The leaking automatic air vent then gets dropped in a bucket with a solution in it. He says the solution is top secret but I know better. It is white vinegar and baking soda. He’ll let the leaking automatic air vent soak in the solution for a few days. Then he pulls it out and tests it on a mock-up pipe he has for this purpose. 90 percent of the time it works like a charm and he puts the automatic air vent in the spare automatic air bleeder box to wait for the next leaking air vent. He said this little trick saved him a few hundred dollars a year in replacing the air vents.
  • Most automatic air vents are sealed and cannot be opened to replace seals or to make any repairs. Furthermore, if you remove it and blow air through the vent it will remove the trash. That is if the problem happens to be trash in the vent.

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Finally, air vents require little maintenance. They still need to be checked on a periodic basis to check for functionality. Additionally, if you have problems with air they need to be checked to make sure they are properly functioning. Additionally, they are used in conjunction with other air elimination devices that can save you from some cold nights and frustration.

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Automatic Air Vents