Within the last two years, I've spoken with engineers charged with designing the mechanical systems to keep the hot water flowing in such bathrooms. One mentioned a recent project requiring 27 gallons per minute of domestic hot water supply to the master bathroom alone. Another told me of an owner's mandate of providing sufficient hot water capacity to supply every hot water outlet in the house (simultaneously) for a continuous draw of 30 minutes. Still another described a project he was retained for in which the owner spent in excess of $100,000 for the master bathroom alone. Finally, a hydronic heating professional in the Philadelphia area told me of a new home he was involved with that contained 17 bathrooms!