My workplace has on-demand hot water. Whenever someone uses it, it kicks on the UPS of my nearby computer. Those things must take some serious power.

I'm planning to buy an "indirect water heater" for home; a hot water storage tank. My oil furnace will heat the stored water when its temp drops below a set point. That way, I'll always have hot water waiting for me and won't start the furnace "on demand" when its tiny reserve of hot water is used. Also, the furnace doesn't have to maintain such high temp to be ready on demand, saving oil.