Automatic air vent Termojet DN20 (3/4")

Automatic air vent Termojet DN20 — a float valve that continuously removes free air and large air bubbles from the highest point of the heating system. Installed on radiators, manifolds, connection assemblies, and any location where air may accumulate. Brass body, 3/4" (DN20) connection, maximum temperature 110°C, working pressure 10 bar.

Technical Specifications

How It Works

Inside the body is a lightweight float. When there is water in the valve chamber, the float keeps the closing element shut. As soon as air accumulates, the float drops and opens the port — air escapes to the outside. Once the air has been discharged, the water lifts the float and the valve closes automatically. The mechanism requires no power supply, no batteries, and no adjustments — simply install and forget.

Where and How It Is Used

• Heating radiators. Installed in place of a manual Maevsky valve at the highest point of the radiator — removes air locks automatically, without annual manual bleeding.
• High point of a circuit. Any loop or riser with an upward run — the valve prevents the accumulation of air pockets that block the circulation of the heat-transfer fluid.
• Distribution manifolds. Installed on each manifold outlet to guarantee air removal after filling or repair.
• New system during initial filling. When commissioning, the system always contains air — the automatic air vent removes it within the first hours of operation without any action from the installer.
• After repair or dismantling of part of the pipework. Refilling inevitably introduces new air — the valve discharges it automatically.

Advantages

• Float mechanism — passive operation without electricity, without batteries, without adjustments.
• Brass body — corrosion resistance and resistance to thermal cycling throughout the entire service life of the heating system.
• Compact DN20 size — suitable for tight installation spaces in manifold cabinets and behind radiators.
• Reliable automatic closure — the valve does not allow water to leak after air has been discharged.

Maevsky Valve vs Automatic Air Vent

The manual Maevsky valve requires regular maintenance: the owner visits each radiator every year, places a container, and manually bleeds the air. The automatic air vent does this around the clock without human involvement. However, there is an important distinction: both the Maevsky valve and the automatic vent remove only free air — large bubbles and air pockets. Invisible micro-bubbles that circulate in the heat-transfer fluid and cause noise, vibration, and reduced boiler efficiency are removed only by the DN20 air separator with a coalescent insert. For a comprehensive solution to heat-transfer fluid cleanliness, also consider the full Termojet separator catalog.

Frequently Asked Questions

Can the valve be installed horizontally?
The automatic air vent must be installed vertically — this allows the float to respond to air accumulation in the upper part of the chamber. Horizontal installation will not ensure correct operation of the float mechanism.

The valve is leaking — what should I do?
The most common cause is scale or rust deposits on the closing element. After flushing the system or installing an air separator with a fluid-cleaning function, the problem disappears.