HVAC & home systems

Heating and cooling planning math — not Manual J, not code compliance: estimate cooling BTU/h from floor area, sum insulation R-values and U-factor, size ventilation CFM from air changes per hour, and find round duct diameter from CFM and velocity. Cite DOE/Energy Star style rules of thumb; confirm with licensed HVAC design for equipment selection.

Square-foot rules of thumb are a starting point and nothing more. A proper load calculation — Manual J in North America — accounts for climate zone, insulation levels, window area and orientation, air leakage, ceiling height, occupancy, and internal heat gains, and it routinely lands well away from the per-square-foot guess. Oversizing is the more common error and carries a real penalty: an oversized air conditioner satisfies the thermostat quickly and short-cycles, which leaves humidity in the air, wears the compressor, and produces a room that feels clammy rather than comfortable. R-values also add only for layers in series, and continuous insulation behaves differently from batts interrupted by framing, where thermal bridging cuts effective performance. Use these figures to frame a conversation with a licensed contractor, not to select equipment.