Technical Foundation
What Is a Air Vent?
Air vents remove trapped air and gas from closed hydronic, chilled water, and hydraulic systems, where air pockets reduce heat transfer efficiency, cause noise, and can lead to pump cavitation or corrosion from oxygen contact with system water. Automatic float-type vents use a ball or float mechanism that rises with the water level inside the vent body — as trapped air accumulates and the float drops, a needle valve opens and releases the air, then reseals once water returns to the float chamber.
Manual (key or coin) vents require an operator to open a small valve with a key or screwdriver to bleed air on a scheduled or as-needed basis, typically used on individual radiators or terminal units where automatic venting isn't cost-justified per unit. Vent sizing and pressure rating must match the system's maximum operating pressure and be installed at high points in the piping where air naturally collects.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Connection Size | 1/8 in to 1 in NPT, or sweat | Larger connections suit high-capacity air eliminators on main loops; smaller for individual terminal units |
| Mechanism | Automatic float vs. manual key/coin | Automatic vents self-operate continuously; manual vents require scheduled operator attention |
| Pressure Rating | Typically 150 psi standard, higher for industrial systems | Must exceed the system's maximum operating pressure with margin |
| Body Material | Brass, cast iron, stainless steel | Brass suits most HVAC water systems; stainless for higher-purity or corrosive fluid systems |
| Temperature Rating | Typically up to 250°F standard duty | Boiler and high-temp hydronic loops require vents rated above the loop's peak operating temperature |
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Applications
Where Air Vent Get Used
Air vents are specified at high points of any closed liquid loop where trapped air or gas would otherwise degrade circulation and heat transfer.
Commercial HVAC Hydronic Systems
Automatic air vents installed at high points of chilled water and hot water loops to maintain circulation efficiency.
Residential & Commercial Boilers
Air vents on boiler supply and return piping preventing airlock that would reduce heating output.
Radiant Floor Heating
Manual and automatic vents on manifolds bleeding air introduced during system fill and makeup water addition.
Hydraulic Power Units
Air vents on hydraulic reservoirs and high points releasing entrained air that would cause spongy or erratic actuator movement.
Solar Thermal Systems
High-temperature-rated vents releasing air and steam pockets from solar collector loops.
Industrial Process Cooling
Air eliminators on process chilled water loops maintaining consistent flow to heat exchangers.
Brands
Air Vent Brands in the Catalogue
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FAQ
Air Vent Questions, Answered
Where should an air vent be installed in a piping system?
Air vents belong at the highest points in the piping system, since air naturally rises and collects there — common locations include the top of risers, the highest point of a boiler loop, and immediately after air separators. Installing a vent at a low point provides no benefit since air won't migrate downward to reach it.
What's the difference between an automatic and manual air vent?
An automatic float-type vent continuously self-operates, releasing air whenever it accumulates without operator action, making it the standard choice for main system loops and high points that need continuous venting. A manual key or coin vent requires someone to physically open it, which is acceptable for individual radiators or terminal units bled periodically but impractical for a whole system's continuous air management.
Why does my automatic air vent keep dripping or leaking water?
A dripping automatic vent usually means the float mechanism's seat has worn or debris is preventing it from sealing fully after releasing air — this is the most common failure mode and the fix is replacing the vent's internal cartridge or the whole vent body, since most are not field-rebuildable beyond a cartridge swap. Persistent dripping under normal operation, rather than during initial fill, indicates the vent needs replacement.
Can I use a standard automatic air vent on a high-temperature boiler loop?
Only if it's rated for the loop's peak operating temperature — a standard-duty vent's seals and float material may degrade or fail at boiler supply temperatures above its rating, causing leaks or vent failure. Check the vent's temperature rating against your system's actual operating temperature, not just its pressure rating.
Do air vents need periodic maintenance even if they're automatic?
Yes — automatic vents can accumulate mineral deposits or debris over time that prevent the float from sealing properly, so periodic inspection for weeping or dripping is recommended, and many are designed with a shutoff valve beneath them specifically so the vent can be serviced or replaced without draining the whole system.
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