Residential HVAC Installation Practice Exam

The main drawback of the extended plenum system is that it often results in lower air velocity at the last takeoffs on the extended plenum. This occurs because as the air travels down the extended plenum, it loses some of its velocity before reaching the last takeoff points. This can lead to reduced efficiency and potentially uneven heating or cooling distribution in the building. Options A, C, and D are not the main drawbacks of the extended plenum system and do not directly relate to the specific issue of lower air velocity at the last takeoffs.