Productivity
Size an HVAC system
A room-by-room load calculation, not a rule of thumb.
Fill it in
Size, construction, windows, insulation and climate.
So the ductwork can be designed from it.
A bigger unit is a worse unit.
Your prompt
Size the system for this property. [the property] Calculate ROOM BY ROOM, not just the whole house. The house total sizes the equipment; the room loads size the ducts, and skipping the second half is why a correctly sized system still leaves one bedroom hot. Use the actual construction: insulation, window type and area by orientation, infiltration and the design temperatures for the location. A rule of thumb per square foot is wrong by a factor that depends on the building. Explain the oversizing risk plainly. An oversized unit short-cycles, never runs long enough to dehumidify, and leaves the house cold and clammy, which the customer experiences as the system not working. Show the inputs so the calculation can be checked.
Use Size an HVAC systemOpens with everything above already filled in.
Why this works
A house total sizes the equipment; the room loads size the ducts, and skipping the second half is why a correctly sized system leaves one bedroom hot. This calculates room by room and explains why an oversized unit is a worse unit.