How to Choose the Right Air Conditioner Capacity by Room Size and Heat Gains (Glendale Guide)

Choosing the right air conditioner capacity is not just about square footage. An undersized unit will run nonstop and struggle on hot afternoons, while an oversized system may cool too fast, leaving humidity behind and increasing wear. For Glendale homeowners, the best approach is to start with room area and then adjust for real heat gains. A simple starting point is 20–25 BTU per square foot for a typical room with average insulation and ceiling height. For example, a 300 sq ft space often needs about 6,000–7,500 BTU/h. Next, refine the estimate using heat inputs: add capacity if the room gets strong afternoon sun, has large west- or south-facing windows, or poor insulation. As a rule of thumb, increase the result by 10–20% for high solar exposure. People and equipment matter too. Add roughly 600 BTU/h for each additional occupant beyond two, especially in bedrooms or living rooms used in the evening. Kitchens, home offices, and media rooms may need extra capacity due to ovens, computers, and electronics; add 1,000–2,000 BTU/h depending on how much equipment runs continuously. Also consider ceiling height and air leakage. High ceilings increase the volume of air to cool; open stairwells and older doors/windows can raise the required BTU significantly. If you’re selecting a whole-home HVAC system, a professional load calculation (Manual J) is the most accurate method, but these steps help you choose a room AC or mini-split size confidently. When in doubt, aim for correct sizing with a quality inverter unit for better comfort and efficiency in Glendale’s warm season.