That does not seem right.

-10С to +20C .. I can't even think of a place with such a swing.

Harsh continental climate winter is maybe -30C to -20C or so.

he's saying that you need to get the temperature to 20 from -10.

Ah. My bad.

Still, if you got this kind of temperature gradients, and I happen to have lived in such a place, you also got at least 100mm mineral wool insulation or eqivalent. Which is poor by the way, and people do invest into 200 or sometimes 300mm. Which makes CO2 and moisture control more of a problem than heating. You basically either heat the outside via ventilation anyway, or invest into heat exchangers. Since complex HVAC systems come with maintenance burden, people just put up 50-100KW-ish heaters, be it natgas or wood and declare the problem fixed.

You could be right, insulation is a lot more effective at keeping houses warm than cold though (greenhouse effect) and heat pumps can dump their waste heat inside.