Just because there are all 2-pole breakers does not mean that the circuits they feed are themselves in balance. For example, perhaps all the receptacles are on shared-neutral or neutral-per-leg multi-wire circuits, and were wired up split. If they were consistently phased, you might end up with everything on the lower half always on one phase side. And then out of habit, people would consistently use maybe the upper outlet first. Then the load can get way out of whack fast.
I've heard of this in kitchens where multi-wire is common. Someone wires up all the lowers on one phase and the uppers on the other. To an electrician it would even make sense as it gives them control over how they use the phases. But the average HO has no idea and probably consistently uses lowers (except where a 2nd is needed). And even GFCI doesn't stop that practice since you can still do neutral-per-leg on the GFCI load side and split ordinary receptacles after that.
FYI, my house plans call for a double duplex at each receptacle location in the kitchen with one duplex on one phase and the other duplex on the other phase upside down, with 2 sets for a total of 4 20-amp circuits. The idea is I have 2 lowers I can use at each location and still balance the load and have the uppers as extras just in case (basically twice what the code requires).
Did you check the current on each phase?
Electric heating certainly can drive up the bill (but hey, no NG or LP bill). I hope the house was built to proper energy conservation codes or better.
And a really crazy thought hit my head first regarding this. What if this was a DIY special and someone wired up one bus to one phase, and the other bus to the neutral, leaving the other phase unconnected? I've heard stories of worse.
Still, all 2-pole breakers has me wondering. Even I'm not that crazy. Do they have AFCI in there (only 2-pole AFCI I've seen are from Cutler-Hammer).
