The entire building is concrete-build, so the floors and walls are super cold in winter, which makes the apartment very chilly. But thankfully a heater is provided to help warm up the space, and the heat function of the A/C unit also helps. The futons (beds) came with pretty thick covers, as well as a fleece blanket on top, so it was nice and warm and comfy for winter.
I really enjoyed sleeping on the tatami floor/platform area, very different compared to your usual business hotels and such.