1/2" x 3/4" Straight Steam Vent Main Air Valve

nVent HOFFMAN 401413 Model 4A Straight Main Steam Air Vent – 1/2" x 3/4"

The nVent HOFFMAN 401413 (Model 4A) is a float-type main air vent designed for use in low-pressure steam heating systems. Configured with a straight body and non-adjustable port, this unit automatically expels air from main lines during start-up and operation, supporting uniform steam distribution and minimizing air binding issues across the system.

Intended for residential and light commercial applications, the 4A is recommended for use in single-pipe and small two-pipe systems. It features a thermostatic float mechanism that closes once steam reaches the vent, preventing loss of steam through the vent opening. For best results, the valve should be installed 6–10 inches above the horizontal return and at least 18 inches above the boiler water line.

Product Features

• Type: Float-type thermostatic vent for main steam lines
• Connection Size: 1/2 in. NPT inlet x 3/4 in. NPT outlet
• Venting Port: Fixed-rate, non-adjustable orifice for consistent operation
• Mounting Configuration: Straight pattern for vertical installation
• Application: Designed for main line air elimination in low-pressure steam heating systems

Technical Specifications

• Model: 4A
• Part Number: 401413
• Operating Pressure: Suitable for low-pressure systems
• Material: Corrosion-resistant components for extended field service
• Installation Height: 6–10 inches above return piping, 18 inches above boiler waterline minimum

Installation Guidelines

The 4A main vent should be installed at the end of steam mains in an upright, vertical orientation. Use thread sealant compatible with steam service. Proper elevation above the return and boiler water line is critical for performance. Avoid overtightening during installation. For optimal system venting, vent sizing should align with system layout and total main length.

Applications

• Steam main venting in one-pipe residential systems
• Air elimination in small two-pipe steam systems
• Suitable for installations where fixed-rate main venting is appropriate