Hi, Based on our lifestyle in Europe, your power requirement calculator has some items missing:- Literally millions of homes here have Gas fired central heating systems, burning natural gas from the North Sea (a quite stupidly, from Russia). They use 40 to 80 watt circulation pumps that run for many hours a day in the colder months. Electricallly heated floor elements can range from 200 watts for a small lobby to say 1200 watts for a larger room. They are more efficient if placed on more underfloor insulation but many people retrospectively install them over older floor screeds with no insulation at all! In colder Scandinavian countries, tens of thousands of car engines are preheated for 2 to 4 hours every winter morning by a 400 watt mains electric element installed in the waterways in the block. Hope this helps. Mike