Plan #2 is a tri-level home, which by ordinary design considerations might have three furnaces, each with attached air conditioning equipment in order to accomplish proper temperature balance between floors. We have seen huge energy bills with this arrangement when the lower floor heats the floor above causing the cooling to start on that floor which we call "runaway cooling". With a single equipment system and zoning, this condition would never occur. In example plan #2 with zoning the main floor is using most of the energy and basement and upper floors are off during most daytime hours. Also, the initial installation cost for the single equipment system with zoning is much less than three equipment systems.