Installation, Service, Load Calculation, and Code/Regulations
Load calculation drives everything
The correct sequence is Manual J (room-by-room load), Manual S (equipment selection within capacity), then Manual D (duct design). Square-foot rules of thumb are explicitly discouraged because orientation, glazing, insulation, infiltration, and internal gains dominate. A load calculation that ignores duct loss and gain undersizes equipment and produces comfort complaints.
Airflow and duct design
Design airflow is roughly 400 CFM per ton of cooling. Total external static pressure on a typical residential air handler should stay near 0.5 in. w.c. - filters, coils, and undersized ducts all consume that budget. Duct sizing normally targets about 0.1 in. w.c. friction rate. Low airflow causes a cold coil, low suction pressure, ice, and a flooded-back compressor; excess airflow hides superheat and reduces latent removal.
Installation and service practice
Use dry nitrogen while brazing, pressure-test with nitrogen, evacuate to 500 microns, and charge by weight when the line set length differs from the factory charge. Provide a P-trap on condensate drains with a secondary pan and float switch on upflow/attic installations. Respect clearances to combustibles, combustion-air requirements, and flue termination distances - these are code items, not preferences.
Codes and regulations
Arkansas adopts the International Mechanical Code with state amendments, alongside the state fire prevention code; local authorities having jurisdiction may be stricter, and the Arkansas HVACR licensing board governs contractor and technician licensing. EPA Section 608 certification is required to purchase and handle refrigerant, and venting is prohibited. Refrigerant safety references ASHRAE 15 and 34, which matter increasingly for A2L systems and room-volume limits.
Worked example: a 3-ton system needs about 1,200 CFM. If the measured temperature drop is 20°F, sensible capacity is 1.08 × 1,200 × 20 = 25,920 Btu/h, which is above nominal - check for an inaccurate thermometer or excess airflow before condemning the equipment.