It may be surprising that just these three systems — mechanical, electrical and plumbing (MEP) — can make up as much as 15% of the total environmental footprint of a building's materials. Even more important is the operation of these systems, particularly mechanical and plumbing. In many cases, pipes and ducts are run willy-nilly after a home has been designed. The frequent result: high energy and water bills. These details are examples of how MEP systems must be integrated into a home's design and then installed according to the design for optimal performance.
High - low transfer grilles
You can't undercut doors enough to provide adequate return air flow with HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. forced air systems (with the door closed, of course). There are four different ways to provide adequate return: dedicated return ducts, above-door offset transfer grilles, high-low transfer grilles, and jump ducts.