For appliances relying on the atmosphere for gas flow, which type of draft do they most likely use?

Natural draft is the correct choice for appliances that rely on the atmosphere for gas flow due to the principles of physics that govern airflow in venting systems. These appliances utilize the natural buoyancy of hot gases to facilitate the upward movement through the venting system. As the gases produced during combustion rise, they create a difference in pressure that allows fresh air to enter the combustion chamber, sustaining the burning process. This type of draft does not require any additional mechanical assistance or power and relies solely on the temperature difference between the hot gas and the cooler outside air.

Understanding the other types of drafts can provide useful context. Mechanical draft involves the use of a fan or blower to actively move combustion gases out of the appliance, which is not necessary for natural draft systems. Combustion draft isn't a standard term for the type of draft in ventilation systems but rather refers to the overall efficiency of combustion in the appliance itself. Induced draft refers to a system where a mechanical means pulls exhaust gases from the vent, which contrasts sharply with the passive nature of natural draft systems. Thus, for appliances that depend on atmospheric conditions for gas flow, natural draft is indeed the correct answer.