Measure the whole open zone
Treat connected spaces without doors as one cooling zone — sum floor areas. A 20×20 living area plus 10×12 kitchen opening is 520 sq ft total, not two separate loads on one head.
Add kitchen load toggle if cooking appliances share the space — ranges and ovens add sensible heat beyond sq-ft math.
Use 25–30 BTU/sq ft as a starting point, then adjust for ceiling height over 8 ft and sunny glass.
Head placement and airflow
- Mount where airflow can reach the farthest corner — often near the kitchen-living boundary
- Avoid blowing directly onto dining tables or sofas — comfort complaints follow
- Ceiling fans help equalize temperature in long rectangular layouts
- Half-walls and pillars redirect airflow — sight lines ≠ air paths
When one head is not enough
L-shaped plans with a jog more than 15 ft from the head may develop hot corners. Second floor open lofts above a great room sometimes need a second head or strong fan circulation.
If bedrooms open off the great room with doors closed at night, size the head for occupied open area only — or add multi-zone for bedrooms.
Open plan worked example
Kitchen 12×14 (168 sq ft) + living 18×16 (288 sq ft) = 456 sq ft open zone. Baseline 456 × 25 = 11,400 BTU. Kitchen load +10% → 12,540 BTU. Nine-foot ceilings +15% → ~14,400 BTU.
Choose a 12,000 or 18,000 BTU head depending on sun and whether you accept the top of range — many open plans land on 12,000 BTU with good insulation. Use the what size AC calculator with kitchen toggle enabled.