When designing HVAC systems and planning building services, it’s important to ensure that adequate space allowances are allocated for plant (equipment) rooms and mechanical services. These allowances help ensure that equipment operates efficiently, is accessible for maintenance, and meets safety standards. These rules of thumb for plant and equipment space allowances in HVAC and building services can serve as valuable guidelines during the design and planning phases. However, it’s essential to adapt these general recommendations to suit the specific needs of each project, considering factors like equipment type, building occupancy, safety requirements, and local codes and standards. Consulting with design engineers and manufacturers during the planning process will help ensure optimal equipment arrangement and functionality. This chapter discusses some rules of thumb for space allowances for HVAC plant and equipment.