I’d have to look at the floor plans, but I’d say about 30 sq m on each of 3 floors, and the roof. Tiny by most western standards.
No central heating, but we have four air-conditioning units for the four rooms in our house (i.e., the ground floor, the 2nd floor, and the two bedrooms that make up the 3rd floor) to cope with both the 35 degree saturated humidity of summer and the sometimes zero degrees winter.
EDIT: Ground and second floor renovation plans (note that the depicted furniture is absurdly small - the furniture we actually bought takes up more space than the diagrams suggest:
EDIT2: Actually @MinuteWalt, I never intended to marry, have kids, or buy a house. Things just happened that way, and I went with the flow. I’ve striven to keep our financial investment as small as possible (have to compromise on that), and it would seem a bit weird to be emotionally invested in a house. I like to think of it as a box - as a base of operations, no more. I just like talking about stuff, especially in English, which I don’t get to use much =)