It's that time of year for me to give "gaijin" instructions on how to survive the subzero temperatures in Japan. Those inside your house, that is.
In Japanese houses, you've probably noticed that central heating does not exist, and instead, central refrigeration is the way of life. On one hand it's nice because you can unplug the refrigerator and spread out all the vegetables on the bed. No more things rotting in the back of the fridge because they're out of sight. On the other hand, you probably did not take the Eskimoing 101 elective in college, so you'll need to learn a few things about living in a walk-in refrigerator.
The first thing you'll need is a wall-mounted heater and air conditioner, which the Japanese refer to as "aircon." This will keep the average person warm enough, but not the average gaijin. Therefore, supplement the "aircon" with a "kotatsu," a small table with a heat lamp under it, to keep your legs warm. If you turn up the kotatsu high enough, it's almost like sitting around a bonfire. You'll find that almost all of your body is warm now, except your fingers. Therefore, sit on your hands. Now don't move until springtime.