Automatic air vent Termojet DN25 (1")

Termojet DN25 automatic air vent — a float valve for continuous removal of free air from the highest points of a heating system. Connection DN25 (G 1"), maximum temperature 110°C, maximum pressure 10 bar, body — brass. The device requires no power supply and no adjustments after installation.

How it works

Inside the valve there is a sealed float. When air or gas accumulates in the upper chamber, the coolant level drops — the float descends and opens the discharge orifice. Air escapes to the outside. As soon as the chamber fills with water again, the float rises and seals the orifice. The cycle repeats automatically, around the clock, without any intervention.

Technical specifications

Where and how it is used

The automatic air vent is installed at the highest point of the system or circuit — where air naturally accumulates. Typical installation locations: the boiler's top manifold, the top of a riser, the highest point of an underfloor heating loop, the top of a distribution header. One valve is installed permanently and then operates independently for the entire service life of the system.

• New system start-up. During the first fill the system contains a large amount of air. The air vent continuously expels it until the system stabilises.
• After flushing or repair. Draining and refilling always introduces new air — the valve expels it without any involvement from the installer.
• Radiator system. Protects against air locks at high points where a manual Schrader/bleed valve is traditionally installed — the automatic valve does the same job without manual intervention.
• Underfloor heating system. Protects the distribution manifold from air pockets that reduce heating uniformity.

Advantages

• Float mechanism — no batteries, no settings, no maintenance.
• Brass body — resistance to corrosion and temperature fluctuations.
• Continuous action — the valve responds instantly as soon as air appears in the chamber.
• Easy installation — standard G 1" thread, can be installed in any orientation.

Limitations and next step

The automatic air vent effectively removes free air — large bubbles and air pockets. Microbubbles (smaller than 1 mm, invisible to the naked eye) circulating in the coolant are not captured by this valve. They accelerate corrosion and reduce heat transfer. If the system is noisy, radiators heat unevenly, or the pump vibrates — this is a signal to install an air separator. The DN25 air separator collects microbubbles through a coalescing insert and removes them permanently. View the full range — Termojet separators — catalogue.