Ro is the sunken hearth built into the floor of a traditional Japanese tea room and is generally used from November to April.
As the weather becomes colder, the kettle is brought closer to the guests, allowing them to feel the warmth of the fire and creating a cozy, intimate atmosphere.
A standard ro measures 1 shaku 4 sun (about 42.4 cm) square, while a dairo (large hearth) measures 1 shaku 8 sun (about 54.5 cm) square.
The change from furo to ro in November is celebrated as Robiraki (the opening of the hearth), one of the most important seasonal events in the Japanese tea ceremony, marking the beginning of a new tea season.
The seasonal change to ro also brings different kettles, charcoal, incense, and hishaku (bamboo ladles), as well as seasonal variations in the procedures for preparing thin tea (usucha), thick tea (koicha), and charcoal arrangement (sumi-temae).
When a tana (display shelf) is used, it is selected to suit the ro.