scojomodena

Sort of, but really we need both. Yes cheaper for most people. But as someone who lives in Minnesota, we definitely get below those temps. By code we require full backup resistive heaters for a heat pump at such a rating which increases the full cost and installation cost. Plus, it is much less efficient than a heat pump (though efficiency lowers as the temp gets colder due to defrost cycles).

Marathon-esque training is pretty good. The difference is really in being able to slow down so you are well within your aerobic zone, below your threshold pace/effort. Running slow enough so you can breathe only through your nose is a good measure. From there, it's about eating and hydration, etc. Ultras are often described as a "an eating competition with some running thrown in". The joints of course is a big deal too, some can do it easier than others.

Also, most people walk a lot, you don't have to run, you just keep making forward progress.

source: I've done a few Ultras and have used a running coach.

I'm in Minnesota. True air source heat pumps aren't great at such temps, but ground source heat pumps it doesn't matter at all. Lot higher install cost though.

Passive income. Or recognizing at least the goal of increasing your income/time ratio.