If you have never been inside a Japanese house, just imagine throwing a bunch of furniture, your computer and your TV into a walk-in freezer. Inhabitants walk around in special thick socks and "chan-chanko," traditional Japanese-style overcoats made for wearing inside the house. Walk into the bathroom and you will find frozen shampoo. A cold Japanese house does have its conveniences, however: You don't have to put the ice cream away when you return from the grocery store.
This is not to say they don't use heaters in Japan. These days, Japan is so modern, they have kerosene fan heaters. If you buy a dozen of these, you can heat your whole house. But most people are content heating just one room and living in there in solitary confinement.
In the United States, we always leave the house heated, even when we are gone. But in Japan, when you come home you have to turn on the heat, then wait for the house to thaw. This means that after you wash your hands, you have to be careful to dry them completely so you don't freeze yourself to a door knob. I'm considering taking out the microwave apparatus from my oven and sticking it in the middle of the living room instead. Then I would have a quick way to microwave the house to warmth when I come home.