How do I calculate heater power?

P = m × c × ΔT / t, where P is power (W), m is mass (kg), c is specific heat (J/kg·K), ΔT is temperature rise (K or °C), and t is heating time (s). For water: c = 4186 J/kg·K.

How much power to heat 100 litres of water?

100L of water = 100kg. To heat by 50°C in 1 hour: P = 100 × 4186 × 50 / 3600 = 5,814W ≈ 6kW. Add 10-20% for losses.

What is the specific heat of common fluids?

Water: 4186 J/kg·K. Air: 1005 J/kg·K. Oil (thermal): ~2000 J/kg·K. Glycol 50%: ~3300 J/kg·K. Ethanol: 2440 J/kg·K.

Should I add a safety factor to heater power?

Yes. Add 10-20% for heat losses through vessel walls and piping. For outdoor tanks, add 30-50%. For batch heating with cold starts, consider peak demand.

How do I convert between volume and mass?

mass = volume × density. Water: 1 kg/L. Air at 20°C: 1.204 kg/m³. Thermal oil: ~0.85 kg/L. Always use the density at the average temperature.

Free Engineering Tool

Heater Power Calculator

Calculate the power required to heat a liquid or air. P = m × c × ΔT / t. Enter mass or volume, specific heat, temperature rise, and heating time.

P = m·c·ΔT/tLiquid & Air#177

Results

Required Power

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Total Energy

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Mass

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With 15% Losses

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Heating Power Formula

Where m = mass (kg), c = specific heat (J/kg·K), ΔT = temperature rise (°C), t = time (seconds).

Heater Power Calculator | P = m·c·ΔT/t | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Results

Heating Power Formula