I am in the process of building a new home and wondered if the cost of enveloping my ducting by furring down in hallways/etc. is worth the extra expense in energy savings over just using standard or insulated ducting in my attic space? Home not in extreme temperature area, 100 degree is very hot and teens is very cold. Northern Arizona Any help in this as well as the best and most effecient type HVAC unit/s greatly appreciated. Thanks PAUL