Where should combustion air terminate indoors?

Where should combustion air terminate indoors?

• A. 2' vertically 1' horizontally from largest natural draft burner
• B. 3' vertically 1' horizontally from largest natural draft burner
• C. 1' vertically 3' horizontally from largest natural draft burner
• D. 1' vertically 2' horizontally from largest natural draft burner

Answer: (D)

Combustion air for indoor appliances must be drawn from a location that stays clear of the burner’s exhaust and heat, so the air entering the appliance is fresh and not preheated or contaminated by the venting flow. The requirement uses the largest natural‑draft burner to set the clearance because that burner represents the worst case for draft and heat effects. Terminating the air intake at least 1 foot above the floor helps avoid taking in heavy dust or cold air from the very floor and reduces floor-level drafts. Keeping the intake at least 2 feet horizontally away from the largest natural‑draft burner keeps it out of the direct path of the exhaust and away from the burner’s heat zone, lowering the chance of backflow or interference with the venting system. Collectively, these minimum distances ensure reliable combustion and reduce the risk of drawing combustion byproducts back into the space. Other distances would either be more restrictive than necessary or fail to meet the required separation from the burner and exhaust, so the 1-foot vertical and 2-foot horizontal separation is the proper guideline.

Combustion air for indoor appliances must be drawn from a location that stays clear of the burner’s exhaust and heat, so the air entering the appliance is fresh and not preheated or contaminated by the venting flow. The requirement uses the largest natural‑draft burner to set the clearance because that burner represents the worst case for draft and heat effects.

Terminating the air intake at least 1 foot above the floor helps avoid taking in heavy dust or cold air from the very floor and reduces floor-level drafts. Keeping the intake at least 2 feet horizontally away from the largest natural‑draft burner keeps it out of the direct path of the exhaust and away from the burner’s heat zone, lowering the chance of backflow or interference with the venting system. Collectively, these minimum distances ensure reliable combustion and reduce the risk of drawing combustion byproducts back into the space.

Other distances would either be more restrictive than necessary or fail to meet the required separation from the burner and exhaust, so the 1-foot vertical and 2-foot horizontal separation is the proper guideline.