This HVAC sizing calculator determines the cooling capacity in British Thermal Units (BTU) and refrigeration tonnage required to condition an indoor living space. Proper sizing prevents both undersizing (where the unit runs continuously without reaching the thermostat setpoint) and oversizing (where the unit short-cycles rapidly, failing to dehumidify the air and leaving the room cold and clammy).

### Cooling Load Physics & Environmental Modifiers Cooling load calculation follows standard residential thermal guidelines: - **Floor Area ($A$):** $ ext{Area (sq ft)} = \text{Length (ft)} \times \text{Width (ft)}$ - **Base Thermal Capacity:** Standard 8-foot ceiling residential spaces require approximately $20\text{ BTU}$ per square foot of living space: $ ext{Base BTU} = A \times 20$ - **Ceiling Height Modifier:** If ceiling height exceeds 8 feet, cooling capacity scales proportionally with the increased air volume: $ ext{Height Multiplier} = \frac{\text{Ceiling Height (ft)}}{8}$ - **Sunlight Exposure Factors:** - Heavily shaded room: $0.9\times$ multiplier (reduce cooling requirement by $10\%$) - Average exposure: $1.0\times$ multiplier - Very sunny room (large south/west-facing windows): $1.1\times$ multiplier (increase capacity by $10\%$) - **Kitchen Appliance Heat Load:** If cooling a kitchen, cooking ranges, refrigerators, and ovens contribute substantial sensible and latent heat, requiring an additional $+4,000\text{ BTU}$. - **Commercial Equipment Sizing & Tonnage:** Manufacturers manufacture window units and mini-split heat pumps in discrete capacity increments (typically 6k, 8k, 10k, 12k, 18k, and 24k BTU). Calculated BTU is rounded up to the nearest 500 BTU increment. Standard refrigeration tonnage is evaluated as: $ ext{Tons} = \frac{\text{Rounded BTU}}{12,000}$

### Worked Numeric Example Sizing an air conditioning unit for a master bedroom: - Length: 20 feet, Width: 15 feet - Ceiling Height: 8 feet - Sun Exposure: Average (1.0) - Kitchen: No (0)

**Step-by-Step Calculation:** 1. Floor Area: $20 \times 15 = 300\text{ sq ft}$. 2. Room Volume: $300 \times 8 = 2,400\text{ cu ft}$. 3. Base Thermal Requirement: $300 \times 20 = 6,000\text{ BTU}$. 4. Ceiling Multiplier: $8 / 8 = 1.0$. 5. Sun Factor: $1.0 \implies 6,000 \times 1.0 = 6,000\text{ BTU}$. 6. Kitchen Addition: $+0\text{ BTU}$. 7. Rounded Commercial Sizing: $6,000\text{ BTU}$ (equivalent to $0.50\text{ Tons}$). *Note:* If this exact 300 sq ft room had 10-foot ceilings and heavy sun exposure ($1.1\times$), the requirement would increase to $(6,000 \times (10/8) \times 1.10) = 8,250\text{ BTU}$ (recommending an 8,500 BTU unit, or $0.71\text{ tons}$).

### Client-Side Processing Note All cooling capacity equations evaluate directly in your browser using local JavaScript math. No home floor plans, room dimensions, or regional location data are sent across any network.