Which appliance relies on direct connection to the gas main for operation?

Direct vent appliances are designed to operate with a direct connection to the gas main to ensure a constant and reliable supply of fuel. These appliances are typically sealed combustion units that utilize outside air for combustion and exhaust their gases directly outside, which enhances efficiency and safety. The direct connection allows for continuous operation without the need for gas storage or interruptions in fuel supply.

In contrast, portable heaters and gas stoves are often designed for convenience, utilizing portable fuel sources or small gas cylinders rather than requiring a direct line to the gas main. This flexibility allows for use in a variety of settings but does not provide the same advantages in terms of constant fuel availability or operational safety as direct vent appliances offer with their direct connection to the gas supply.