Definitely a loaded question with way too many variables! We have NG and wood heat. We can heat and cool (via MS system's) only the areas of our New England house which we chose to do so. Realistically, we can, and typically do, get by with <10kW/day. With that said, if I'm making the commitment to build a system, it's going to be large enough to support our expected future needs, and also replace some, if not most, of our fossil fuel needs. So basically, we could use as little as 7kW/day, or use as much as 10x that if we wanted to. I guess it all boils down to how much electricity you want to use or rely on? Either way, I like having plenty of redundant options for energy, and not be at the mercy of any of them. One thing has become crystal clear to me, there will be major a energy crisis in the not-too-distant future. Better to be prepared than not IMO!