Actually it is the other way around. The houses designed for electric heating usually don't have any heating pipes but just resistive heaters as part of the flo

Actually it is the other way around. The houses designed for electric heating usually don't have any heating pipes but just resistive heaters as part of the floor. You cannot convert that to heat pumps, you have to build a new heating system into the house including laying pipes, new floors. On the other side, if you have a central heating system, you can replace the burner with a heat pump and leave the rest mostly unchanged. I say mostly, as you want to optimize the whole system towards lower water temperatures to get higher efficiencies of the heat pumps. But this can be done, and if you have in-the-floor heating already, this can be skipped as that works with low water temperatures anyway.