I like your idea about the AC units being used for heating. However, I disagree about the fireplaces, they are not efficient to warm up a whole house. In my experience, it's usually one wood burning stove per room, and it's definitely possible to connect several stoves to same chimney stack. Would be nice if cooking stoves could also be used to warm up the place, especially those that look like they use wood as fuel, and also if there was a system for the heat to linger on for a while. From what I noticed it tends to disappear the moment you turned off the fireplace. Those terracotta fireplaces that came with Business and Hobbies certainly look like they use refractory bricks which give off heat long after the fire is extinguished.
