Sorry, but I don't buy this. If this were true, it would be no use at all to insulate your house. How do you explain then that, back in the days when people did not insulate their houses, they easily needed a 35 to 40 Kw furnace to warm their houses to a comfortable temperature? If they now insulate that same house properly, they could easily do with a furnace of about 10 to 12 Kw (or even less) to also warm up that same house to the same temperature. The more powerful heater obviously also consumes a lot more fuel (not sure if its also about four times as much, but in any case a lot more)

And what about passive houses, which don't even have a central heating system anymore, but simply a LOT of insulation in the walls of their houses?

I know for a fact that, due to the thick amount of insulation in the walls of my house, my heating system doesn't have to work very hard to keep the temperature on the same level. It only switches on maybe once every two hours, and even then only for a few minutes. If I turn it off, letting the whole house cool down (which, granted, could take a few days), the system would be running for at least a day, none stop, to get the temperature back to the comfort level it was before. It would certainly consume more power during that 24 hr heating up period than it would have if I would just would have let it run constantly, only switching on a few minutes every two hours, with a total of maybe two hours per day.