[nkurz]

I used coal because the GP said they were in an area where coal and natural gas were primarily used for generation. Since coal is used as part of the blend, it seemed reasonable to consider it as a worst case scenario for efficiency. I wasn't objecting to the general conclusion, just the implication that there was clearly no case where natural gas heat might beat a heat pump.

I'd happily concede that in all locations in California a heat pump will be more efficient when averaged over the entire year. I'm less sure about Winnipeg or Whitehorse, especially if we are looking at shorter timescales. Did jmchphers indicate somewhere that he was in California, or even the US? If he's somewhere very cold, I think we still need to at least run the numbers.

(I should probably also add that I've got a heat pump hot water heater and heat pump dryer. I'm a big fan of the technology---I just don't think it's always the head-and-shoulders winner for all people in all locations at all times.)