Manual J is a calculation of house’s square feet, window space, insulation, and the number of occupants. These measurements comprise the heat gain of the house. Design parameters of climate (usually average high/lows) and what the occupant would like to keep temperature set to are also recorded. These combined calculations provide the recommended size of cooling/heating needed.
Manual J calculations determine the size of HVAC equipment needed, the size of ducts needed, the number and size of supply and return outlets in each room. It prevents under sized systems, noisy systems, imbalances (hot and cold spots) in the system and higher operating costs.
A Manual D calculation and drawing is developed with the correct ducting, airflow, registers, and unit performance to meet heating, cooling and ventilation requirements of the building.