Water (Liquid)
Air (Dry)
Aluminum
Copper
Iron / Steel
Ethanol
Oil (Typical)
Custom
Select a material to auto-fill Specific Heat Capacity.
Typical electric heater: 95-100%, Gas: 70-90%
0 Watts
Temperature Rise (ΔT):0 °C
Total Thermal Energy Needed:0 kJ
Heating Rate:0 °C/min
Actual Power (with Efficiency):0 kW
function updateSpecificHeat() {
var select = document.getElementById('materialSelect');
var input = document.getElementById('specificHeatInput');
if (select.value !== "0") {
input.value = select.value;
}
}
function calculateHeating() {
// 1. Get Inputs
var mass = parseFloat(document.getElementById('massInput').value);
var cp = parseFloat(document.getElementById('specificHeatInput').value);
var t1 = parseFloat(document.getElementById('startTemp').value);
var t2 = parseFloat(document.getElementById('targetTemp').value);
var timeMins = parseFloat(document.getElementById('timeInput').value);
var effPercent = parseFloat(document.getElementById('efficiencyInput').value);
// 2. Validate Inputs
if (isNaN(mass) || isNaN(cp) || isNaN(t1) || isNaN(t2) || isNaN(timeMins) || isNaN(effPercent)) {
alert("Please fill in all fields with valid numbers.");
return;
}
if (timeMins <= 0) {
alert("Time must be greater than 0 minutes.");
return;
}
if (mass <= 0) {
alert("Mass must be greater than 0 kg.");
return;
}
// 3. Calculation Logic
// Temperature difference
var deltaT = t2 – t1;
var isCooling = deltaT < 0;
var absDeltaT = Math.abs(deltaT);
// Energy required (Joules) = Mass (kg) * Specific Heat (J/kgC) * Delta T
var energyJoules = mass * cp * absDeltaT;
// Time in seconds
var timeSeconds = timeMins * 60;
// Theoretical Power (Watts) = Joules / Seconds
var theoreticalPowerWatts = energyJoules / timeSeconds;
// Efficiency Factor (Decimal)
var effDecimal = effPercent / 100;
if (effDecimal <= 0) effDecimal = 1; // Prevent divide by zero
// Actual Power Required (accounting for heat loss/inefficiency)
var actualPowerWatts = theoreticalPowerWatts / effDecimal;
var actualPowerKW = actualPowerWatts / 1000;
// Rate of Heating
var heatingRate = absDeltaT / timeMins;
// Energy in kJ
var energyKJ = energyJoules / 1000;
// 4. Update UI
var resultDiv = document.getElementById('result-container');
resultDiv.style.display = 'block';
// Format numbers nicely
document.getElementById('powerResult').innerText = Math.round(actualPowerWatts).toLocaleString() + " Watts";
document.getElementById('deltaTResult').innerText = deltaT.toFixed(1) + " °C";
document.getElementById('energyResult').innerText = Math.round(energyKJ).toLocaleString() + " kJ";
document.getElementById('rateResult').innerText = heatingRate.toFixed(2) + " °C/min";
document.getElementById('actualPowerResult').innerText = actualPowerKW.toFixed(2) + " kW";
// Change color for cooling
if (isCooling) {
document.getElementById('powerResult').style.color = "#3498db"; // Blue for cooling
document.querySelector('.calculator-title').innerText = "Cooling Load Calculator";
} else {
document.getElementById('powerResult').style.color = "#d35400"; // Orange for heating
document.querySelector('.calculator-title').innerText = "Thermal Power & Heating Rate Calculator";
}
}
How to Calculate Rate of Heating and Thermal Power
Understanding how to calculate the rate of heating is essential for engineers, students, and HVAC technicians. Whether you are sizing a water heater, designing an industrial process, or simply trying to figure out how long it will take to boil a pot of water, the physics remains the same.
This calculator determines the power required (in Watts or Kilowatts) to heat a specific mass of a substance by a certain temperature degree over a set period of time.
The Physics Formula
To calculate the thermal energy required to change an object's temperature, we use the specific heat capacity formula:
Q = m × c × ΔT
Where:
Q = Thermal Energy (Joules)
m = Mass of the substance (kilograms)
c = Specific Heat Capacity (J/kg·°C)
ΔT = Change in temperature (Target Temp – Initial Temp)
Calculating Power (Watts)
Energy tells us the total work needed, but Power tells us how fast that work is done. To find the required heater size (Rate of Heating), we divide the total energy by the time allowed:
P = Q / t
Where t is time in seconds. If your system is not 100% efficient (which is true for all real-world systems), you must divide the result by the efficiency percentage (decimal form) to get the actual input power required.
Glossary of Terms
Specific Heat Capacity
This metric defines how much energy is needed to raise 1kg of a substance by 1°C. Water has a very high specific heat (4,186 J/kg·°C), which is why it takes a lot of energy to boil water compared to heating a piece of metal like copper (385 J/kg·°C).
Efficiency
In the real world, heat is lost to the surrounding environment (insulation loss). Electric immersion heaters are highly efficient (near 95-100%), while gas burners may only be 70-80% efficient. This calculator adjusts the final power requirement based on your efficiency input.
Example Calculation
Let's say you want to heat 50 kg of water from 20°C to 80°C in 30 minutes.
Mass (m): 50 kg
Specific Heat (c): 4,186 J/kg·°C
Temperature Rise (ΔT): 60°C
Energy (Q): 50 × 4,186 × 60 = 12,558,000 Joules
Time (t): 30 mins = 1,800 seconds
Power (P): 12,558,000 / 1,800 = 6,976 Watts
You would need approximately a 7 kW heater assuming 100% efficiency.