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A/C Sizing Guide
What is BTU?
BTU (British Thermal Unit) measures cooling capacity. One BTU is the energy needed to raise 1 pound of water by 1°F. Air conditioners are rated by how many BTU/hr they can remove from a space. A 12,000 BTU unit = 1 ton of cooling.
Caribbean Climate Considerations
The Caribbean experiences year-round high temperatures (88–95°F) and humidity (60–85%). This means:
- AC units work harder and longer than in temperate climates
- Humidity removal is as important as temperature reduction
- Oversizing wastes energy; undersizing leaves rooms uncomfortable
- Sun exposure and window orientation significantly affect load
Insulation Quality Guide
Rating
BTU/sqft
Description
Poor
35
Concrete block, no ceiling insulation, metal roof
Average
30
Basic ceiling insulation, standard construction
Good
25
Wall + ceiling insulation, double-pane windows
Excellent
20
Full insulation, radiant barrier, Low-E windows
SEER / EER Ratings
- EER (Energy Efficiency Ratio) = BTU/hr per watt at a single test point
- SEER (Seasonal EER) = average over a cooling season
- Window units: EER 8–12 (SEER 10–14)
- Split units: EER 10–15 (SEER 14–21)
- Inverter splits: EER 12–18 (SEER 18–25)
- For Caribbean, minimum SEER 16 recommended for cost savings
Window Selection & Solar Gain
Windows are a major source of heat gain:
- Single Pane: 100% solar heat gain (worst)
- Double Pane: 75% of single pane gain
- Tinted / Low-E: 55% of single pane gain (best)
- West-facing windows get the most afternoon sun (700 BTU/window)
- South-facing windows get the most total sun (800 BTU/window)
- North-facing windows get the least sun (400 BTU/window)
Standard AC Unit Sizes
BTU
Tonnage
Typical Use
9,000
0.75 ton
Small bedroom
12,000
1.0 ton
Bedroom / small office
18,000
1.5 ton
Living room / large bedroom
24,000
2.0 ton
Large living area
30,000
2.5 ton
Open plan area
36,000
3.0 ton
Large commercial space
48,000
4.0 ton
Commercial / warehouse
60,000
5.0 ton
Large commercial
Tips for Reducing Cooling Load
- Add ceiling insulation (can reduce load 15–25%)
- Install tinted or Low-E window film
- Use light-colored roof paint or coatings
- Plant shade trees on west and south sides
- Seal gaps around doors and windows
- Use ceiling fans to supplement AC
- Keep curtains/blinds closed during peak sun hours
- Service AC units regularly (clean filters monthly)
Disclaimer: This calculator provides estimates for preliminary AC sizing. Actual cooling requirements depend on site-specific conditions including exact location, building construction, humidity levels, internal heat loads, and ductwork design. Always consult a qualified HVAC professional for detailed cooling load analysis and equipment selection.
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