What is the primary benefit of using direct-vent and sealed combustion appliances in terms of indoor air?

• A. They require more maintenance
• B. They cool indoor space by absorbing heat
• C. They require no venting at all
• D. They draw combustion air from outdoors and exhaust to outdoors

Answer: (D)

Direct-vent and sealed combustion appliances are designed to keep indoor air separate from the combustion process. They draw the air they need for burning from outside and vent all combustion gases to the outdoors. This means the living space isn’t using indoor air for combustion, and combustion byproducts aren’t entering the home. The result is better indoor air quality and fewer issues with room pressure and air infiltration.

Other statements don’t capture this IAQ advantage: they don’t rely on outdoor air for combustion, they don’t eliminate indoor air involvement in combustion, and they still require venting to the outside.