Aircon BTU Sizing

BTU/hr (British Thermal Units per hour) is how aircon capacity is rated — bigger BTU = more cooling power. Picking the wrong size is the most common aircon mistake: undersized units run nonstop and never cool the room; oversized units short-cycle (turn on, blast cold, turn off) and don't dehumidify, leaving the room cold but clammy. Right-sizing is more important than buying the most expensive unit.

US calculators typically use ~500 BTU/sqm (or ~20 BTU/sqft) because their climate is cooler with lower humidity. The Philippines is hotter year-round with high humidity, so we use ~650 BTU/sqm as the tropical baseline. Adding sun exposure on top of that matters more here — a west-facing room without curtains can absorb significant heat through walls and windows from 1 PM onwards.

Rough PH aircon ladder: 0.5 HP ≈ 5,000 BTU, 0.75 HP ≈ 7,500 BTU, 1.0 HP ≈ 9,500 BTU, 1.5 HP ≈ 12,000 BTU, 2.0 HP ≈ 18,000 BTU, 2.5 HP ≈ 22,000 BTU, 3.0 HP ≈ 28,000 BTU. Different brands rate slightly differently — Daikin's '1.0 HP' may be 9,300 while LG's may be 9,800. Compare BTU ratings, not HP labels, when shopping.

AC cools air volume, not just floor area. A 12 sqm room at 2.4 m ceiling has 28.8 cubic meters. The same room at 3.0 m ceiling has 36 cubic meters — 25% more air to cool. Older PH homes (1970s/80s) and many condos have 2.7–3.0 m ceilings; pre-war wooden houses can hit 3.6+ m. Our default 2.4 m is for typical modern build.

West-facing windows with no shade can add hours of direct solar heat gain during peak afternoon (1–5 PM) when ambient temps are already at peak. Concrete walls absorb and re-radiate at night. Heavy curtains, reflective film, or external shading cuts this dramatically — if you can fix the heat-in problem at the window, you might not need the bigger AC.

Anything left on for hours that generates measurable heat: TVs (especially older plasma/LCD), desktop PCs and monitors, gaming consoles, projectors, halogen lights, electric kettles, sound systems. Each contributes ~600 BTU of cooling load. Phone chargers, LED bulbs, and fans don't count.

Oversized aircon short-cycles: hits target temp fast, switches off, then humidity creeps back in, switches on again 5 minutes later. The room feels cold but damp — fungus, mildew, swollen wooden floors. You also waste 20–30% more electricity on startup surges versus a right-sized inverter running steady. Inverter aircons handle slight oversize better than non-inverter, but right-sizing still wins.

Inverter wins for any usage above ~3 hours/day. It runs 30–40% cheaper, lasts longer, runs quieter, and handles partial loads much better. Non-inverter is only worth it for purely intermittent use (guest room, rarely used) where the upfront ₱8K–15K premium won't be recouped before the unit dies.

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