Kotsatsu

this is a traditional japanese hearth furniture, whereby a pit is cut in the floor, 40cms deep with the table sitting above, and a heater in the pit to warm cold feet!!
great for winter in classrooms!!!

it traps the warm air from below to use, while the rest of the room is drafty.

"Generally, a blanket is draped over the frame under the table-top. A person then sits on the floor with their legs (or most of their body if napping) under the table with the blanket draped over the lower body. Though this only heats up the lower body, it can keep one quite comfortable even in an unheated/under-heated room. In the summer, the blanket may be removed and the kotatsu can be used as a normal table.
Most Japanese housing is un- or under-insulated, and they rely primarily on space heating. Heat is expensive because of the lack of insulation, and the draftiness of housing. A kotatsu is a relatively inexpensive way to stay warm in the winter, as the futons trap the warm air.
The kotatsu was originally designed for people wearing Japanese style clothes, where the heat would enter through the bottom of the robes and exit around the neck, thus heating the entire body." - Wikipedia