What type of heating appliance must be separated by 2 hour rated construction?

A heating appliance that must be separated by 2-hour rated construction is typically one that poses a significant fire hazard due to the nature of its operation. Unprotected open flame appliances fall into this category because they have exposed flame that can ignite nearby combustibles if not adequately contained.

This critical separation helps prevent the spread of fire and ensures that any potential fire incident can be contained more effectively. The 2-hour rating provides a timeframe during which the construction can withstand heat and resist fire spread, enhancing overall safety in a building.

In contrast, electric heaters generally do not pose the same level of risk as they operate without an open flame. Gas furnaces, while they do have combustion, are typically installed and designed with safety measures that reduce the risk of ignition and the need for such extensive separation in most contexts. Radiant heaters, depending on their design and installation, may not require the same level of fire-resistance construction as unprotected open flame appliances.