Hi Alan, sorry to be so late getting back to you on your experience with heat pumps. I believe we are both right at the same time. Under some circumstances (fairly modern, well insulated construction with internal party walls like in your condo) you can get by on heat pumps alone if you can tolerate some cold days in winter. If our house was at 65F I would be divorced. I might be able to squeak by on heat pumps alone if I could tolerate 65F. But I can’t keep our detached home at 70F on the heat pumps alone if it is below about 20F out. I manage this very carefully (eg I put the furnace on for an hour) and have got our annual heating oil use down to about 30 gallons a year. Before the “Fab Four” it was 3,000. So even a detached house at 70F is very close to being able to be heated year round in MA with heat pumps alone. Even if it can be done, it gets very expensive because heat pumps get less efficient at low temperatures. The economic cross over point (the temperature below which it is cheaper to heat with natural gas) is often around 30F. So, even if it can be done, it is very expensive to do so.