My electric bill is the same year round within a few dollars. 2000 sq ft on the top of a hill, where wind speed is measured in chain links. No kids at home, just 2, uh, not quite of retirement age. We have what is called a Pump & Dump. Pump the water from the ground, extract or add heat to it then dump it out into the pasture. The domestic hot water is warmed prior to entering the water heater in the process but I have not studied it for just how much that helps. Zoned with most of the bells and whistles. Not cheap. We lucked and got the tax credit and a rebate from POCO. The back up strips do not come on even in the coldest weather, unless you bump the stat up several degrees.
and yes we have done several. My unit is fed with a 2 pole 30, a 2 pole 40 and a 2 pole 50. Typically one or two 260s and a 230