air source heat pumps, though they're improving won't do well in extreme cold; even if they can operate they'll still be running at much lower efficiency.
For temperatures significantly into negative territory a ground source heat pump would perform far better, where it can draw on a source of heat that will always be at least above freezing.
A hybrid system doesn't seem like a bad trade-off though..
^^This, exactly. First see how far you can push a decent relational DB, then try harder. When you really can’t push it any harder, or it becomes uneconomical to do so, _then_ look at graph solutions.
Depends if the French are as disposed to shooting each other as Americans are. Over 10,000 Americans are killed by gun violence every year. This is excluding ~19,000 firearm suicides. Since 9/11, the number of U.S. citizens killed in terrorist attacks each year has never surpassed 75.