The Room Size Chart: HP to Square Meters
Definition
BTU (British Thermal Unit): the industry measure of cooling power — 1 HP ≈ 9,000 BTU/h in Philippine consumer aircon ratings, though actual ASHRAE-rated capacity may vary by up to 10%.
Philippine HVAC practice groups aircon capacity into horsepower (HP) ratings mapped against usable floor area. As a baseline, a 0.5 HP unit cools rooms up to 15 sqm; 0.75 HP covers 16–22 sqm; 1.0 HP handles 23–30 sqm; 1.5 HP suits 31–45 sqm; 2.0 HP fits 46–60 sqm; and 2.5–3.0 HP units serve 61–90 sqm spaces such as open-plan living areas. These ranges assume a standard 2.7–3.0 m ceiling, moderate Philippine climate conditions, and occupancy of two to four people. The chart is a starting point, not a final answer — Philippine homes often deviate from standard conditions due to west-facing walls, full glass facades, and proximity to the roof.
Factors That Affect Sizing in the Philippine Climate
Definition
Cooling Load: the total rate of heat that an air conditioning system must remove from a space to maintain the target temperature. Expressed in BTU/h or kilowatts.
Several Philippine-specific conditions push sizing beyond the basic chart. Direct sunlight on a west-facing wall adds roughly 10–15% to your cooling requirement. Every additional person beyond two occupants adds approximately 500 BTU/h. High ceilings (above 3.2 m) increase volume by 15–25%, requiring a step-up in capacity. Rooms on the top floor directly under a concrete or galvanized iron roof absorb radiant heat throughout the afternoon, often mandating a full HP size increase. Kitchen placements near the cooking zone add heat load from appliances. Inverter units sized at 100–110% of the calculated load handle peak demand efficiently; non-inverter units should be sized closer to 80–90% so they cycle properly rather than short-cycling.
The Philippine Cooling Load Calculation Formula
A simplified field formula used by Philippine installers: Cooling Capacity (BTU/h) = (Floor Area × 600) + (No. of Occupants × 500) + (No. of Windows × 1,000) + Appliance Load (in BTU/h). The 600 BTU/sqm factor accounts for average Philippine climate and construction materials. Convert the result to HP by dividing by 9,000. Always round up to the next standard HP size. For offices with high equipment density — servers, copiers, or dense workstations — the appliance load item becomes critical. A single desktop PC adds roughly 341 BTU/h; a laser printer adds 512 BTU/h. ASHRAE standards recommend a full load calculation for spaces above 100 sqm.
Philippine Example
A 24 sqm Quezon City bedroom on the top floor, west-facing, with 2 occupants and 1 window: (24 × 600) + (2 × 500) + (1 × 1,000) = 14,400 + 1,000 + 1,000 = 16,400 BTU/h, plus 15% west-wall adjustment = ~18,860 BTU/h ÷ 9,000 = 2.1 HP. Select a 2.0 HP inverter unit, which at 100% load handles this demand within its operating range.
Inverter vs Non-Inverter Sizing Differences
Inverter aircons can modulate compressor speed, so they tolerate being sized 10–20% above nominal load — this actually improves efficiency because the unit runs at partial capacity rather than cycling on and off. Non-inverter units have fixed-speed compressors and should be sized at 80–90% of peak load to ensure they run long enough for proper humidity dehumidification. Oversizing a non-inverter results in short cycling: the unit cools quickly but never runs long enough to remove humidity, leaving a cold-but-damp feeling common in Philippine homes during the wet season from June to October. Always consider your wet-season comfort baseline when sizing, not just the peak April–May heat.
Common Sizing Mistakes in Philippine Homes
Mistake 1: Using carpet area instead of total floor area — always measure the room's full dimensions including under furniture. Mistake 2: Ignoring the roof factor — rooms directly under galvanized-iron roofs in Cavite, Laguna, and Bulacan suburbs heat up 5–8°C more than those with ceilings below the roof deck. Mistake 3: Buying the cheapest unit in the target HP — capacity is rated at standard conditions (ISO 5151), not Philippine peak summer. Units from non-JMA-certified brands may perform 15% below label. Mistake 4: Using residential sizing rules for sari-sari stores or small offices — commercial occupancy and appliance loads change the calculation significantly. Always request a written load calculation from your installer before purchase.
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