Heating, Ventilation, and Air Conditioning (HVAC) systems are crucial components of modern buildings, ensuring a comfortable indoor environment for occupants. Accurate calculations are essential for designing and selecting HVAC systems that meet the required heating and cooling loads. Microsoft Excel is a widely used software for performing these calculations due to its ease of use and flexibility. This paper presents a comprehensive guide on creating an HVAC calculation Excel sheet for 2021, covering various aspects of HVAC design, including heating and cooling load calculations, duct sizing, and system selection.