I really can't see the advantage of 3-phase in anything other than industrial situations where the smooth starting and running of large-scale electric motors is a concern. 230V single phase supplies quite obviously can and do work perfectly effectively and safely in UK/Ireland for everything including heating and cooking. 380/400/415 volt 3phase systems just add extra shock hazzards and excessively complicated wiring for no good reason.
In heavy load domestic situations here where electric space heating is used a second 80 - 100amp supply (not necessarily from a different phase) is sometimes added specifically for that purpose. The heating system would be metered seperately, fused seperately and treated as a completely seperate supply.
