ASHRAE-based 35°C tropical design
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Home HVAC Heat Load Calculator

Heat Load Calculator (AC Tonnage).

Calculate the right AC capacity in tons of refrigeration (TR) for any space in Sri Lanka. ASHRAE-based methodology with sensible + latent load split, tropical design conditions, and PDF output. Free, no signup.

ASHRAE methodology Sensible + latent split System type recommendation Branded PDF output

1Project & Space Type

Pick the space type to seed sensible defaults. You can edit everything below.

2Room Dimensions

Enter floor area or length × width. Higher ceilings increase heat load (more volume to cool).

Floor area: 24 m² · Volume: 72 m³

3Design Conditions

Standard Sri Lankan design: 35°C / 70% RH outdoor, 24°C / 50% RH indoor. Adjust for hill country (cooler outdoor) or specialised spaces (server rooms 22°C, restaurants 23°C).

Δ Temperature: 11 °C · Δ Humidity: ~10 g/kg

4Building Envelope (External Heat Gain)

Heat conducted through walls, roof, glass and floor. Glass facing East/West gets direct sun load — much higher than North/South in tropical Sri Lanka.

Walls — external area per orientation (m²)

Roof / Ceiling

Glass / Glazing — area per orientation (m²)

Partition / Floor (to unconditioned space)

Walls between cooled and uncooled space
Only if floor below is unconditioned
Typically 5-8°C

5Internal Heat Gain

People, lighting, equipment. People generate both sensible (body heat) and latent (sweat / breath moisture) loads.

People

Lighting

% of lights ON at peak
Leave blank for auto from W/m²

Equipment / Appliances

~150 W each
~70 W each
~250 W each (avg)
Servers, kitchen, motors, etc.

6Fresh Air / Ventilation

ASHRAE 62.1 minimum: 7.5 L/s per person + 0.3 L/s per m² floor area for offices. Restaurants and kitchens need much more. Ventilation adds both sensible and latent load.

Calculated fresh air: — L/s
Engineering disclaimer. This calculator uses an ASHRAE-derived simplified method suitable for HVAC equipment selection. Final design should be validated using full hourly load simulation (e.g., HAP, Trane TRACE, IES VE) for projects above 50 TR or with complex schedules. NativeWay's HVAC engineers can run a detailed simulation as part of any design-build engagement.