I actually did a back-of-the-envelope analysis along those lines. (I might have forgotten to mention that I was an environmental economics major...) My best near-term ROI? Same conclusion: an electric resistance furnace. Cost next to nothing and would easily pay for itself the first year vs what I was paying out in propane. The savings would continue to pile up year after year. Couldn't quite pull the trigger though.... externalities and whatnot.

The far end of the envelope vs heat source spectrum is when campers sleep next to an open fire...no envelope at all.

It sounds like Blake's house wasn't far from that extreme.

Typical exit air temps at the registers of mid-efficiency scorched-air fossil furnaces are north of 120F but usually under 140F. With condensing burners it's usually under 125F (if not much under), but going with a more appropriately sized and condensing propane burner will still do a lot for comfor. With hydro-air it can be anything, but most are set up to run between 110F-125F. (On my own hydro-air zone I run it with ~95-100F output at the coolest register, the warmest registers run 105-110F, using ~125F water.)

But even condensing propane is an insanely expensive way to heat at this year's prices.

It's a rare market where electric hot air is dramatically cheaper than 80% efficiency propane- in many markets they're roughly equal even at last year's prices. (Blake must have fairly cheap electricity!) But in high-priced electricity markets (like southern New England) propane is usually cheaper than resistance electricity when looking at 5-year price averages. The trend on propane prices (like heating oil prices) isn't favorable, and FAR more volatile than the regulated retail prices of electricity.

Electric baseboard or electric radiant can be more comfortable and is easily micro-zoned, which can produce double-digit savings over electric hot air. But the externalities indeed drive us toward heat pump technologies, even when the efficiency alone isn't good enough for a decent short-term ROI.

Off peak electric rates can make electric much more attractive but then you have the thermal storage issue.

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