An adjustable device for varying the size of the air inlet or inlets regulating primary or secondary air is called what?

An adjustable device for varying the size of the air inlet or inlets regulating primary or secondary air is called what?

• A. Draft hood
• B. Regulator vent
• C. Orifice
• D. Air shutter

Answer: (D)

The adjustable device that varies the size of the air inlet(s) to regulate primary or secondary air for combustion is the air shutter. By opening or closing the shutter, you control how much air enters the burner before combustion, which tunes the gas–air mixture and flame behavior. Properly set air shutter ensures a stable, efficient flame—typically a blue flame with complete combustion. If too little primary air is admitted, the flame can become yellow and smoky, indicating incomplete combustion; adjusting the shutter helps prevent this. The other terms refer to different parts with different roles: a draft hood is part of the venting system to prevent backdrafting of combustion products, a regulator vent is the outlet for a gas pressure regulator, and an orifice is a fixed opening that meters gas flow, not air.

The adjustable device that varies the size of the air inlet(s) to regulate primary or secondary air for combustion is the air shutter. By opening or closing the shutter, you control how much air enters the burner before combustion, which tunes the gas–air mixture and flame behavior. Properly set air shutter ensures a stable, efficient flame—typically a blue flame with complete combustion. If too little primary air is admitted, the flame can become yellow and smoky, indicating incomplete combustion; adjusting the shutter helps prevent this.

The other terms refer to different parts with different roles: a draft hood is part of the venting system to prevent backdrafting of combustion products, a regulator vent is the outlet for a gas pressure regulator, and an orifice is a fixed opening that meters gas flow, not air.