Engineering
Heat Transfer Calculator
Calculate steady heat-transfer rate from overall U-value, area, and temperature difference; convert it to kilowatts; accumulate period thermal energy; and report heat flux. The guide explains direction, composite resistance, steady-state assumptions, and why energy use is not automatically electrical cost.
Heat-transfer rate-
Heat-transfer rate-
Period thermal energy-
Heat flux-
Decision view
Hot-to-cold heat-transfer path
Hot-to-cold heat-transfer pathOverall U-value, transfer area, and temperature difference drive the steady heat rate from the hot boundary to the cold boundary.
Exact scenario comparisonTemperature difference (K) changes while all other entered assumptions remain constant.
| Temperature difference (K) | Heat-transfer rate | Heat-transfer rate | Period thermal energy | Heat flux |
|---|
How to use Heat Transfer Calculator
- Enter a U-value that represents the complete assembly and boundary film conditions.
- Enter effective transfer area and the signed or magnitude temperature difference appropriate to the intended heat-flow direction.
- Use the heat rate for steady duty and multiply by representative hours only when that duty is sustained.
Calculator guide
Understanding Heat Transfer Calculator
The U-value method combines all modeled conduction and convection resistances into one coefficient. This page makes the temperature driving force, area, heat rate, energy, and heat flux visible as separate quantities.
Calculation method
How the calculation works
Multiply overall U-value, transfer area, and temperature difference to estimate steady heat-transfer rate and period energy. Heat rate Qdot = U × A × ΔT. Heat flux q'' = UΔT, and period thermal energy equals heat rate in kW multiplied by operating hours.
Thermal resistance
What is hidden inside an overall U-value
The simple multiplication is useful because prior resistance calculations have been condensed.
Do not reuse a U-value when construction, orientation, air speed, or boundary conditions differ materially.
Worked situations
Practical examples
- U = 2.4 W/m²K, area 85 m², and ΔT = 18 K produce 3,672 W or 3.672 kW.
- Heat flux is 43.2 W/m² across the modeled assembly.
- At constant conditions for 2,200 hours, thermal energy is approximately 8,078.4 kWh.
Better inputs
Useful tips
- Use indoor-outdoor or hot-cold temperatures that correspond to the U-value boundary definition.
- Separate opaque surfaces, glazing, thermal bridges, infiltration, and ventilation when they have different models.
- Convert thermal energy to fuel or electricity with equipment efficiency or COP rather than treating them as identical.
Before relying on the result
Limitations and common mistakes
- The formula assumes steady one-dimensional heat transfer and constant U, area, and temperature difference.
- Thermal mass, solar gain, radiation exchange, moisture, air leakage, bridges, fouling, and control cycles are excluded.
- The period energy is a constant-duty multiplication, not an hourly weather or process simulation.
Reference
Key terms
- U-value
- Overall heat-transfer coefficient through the complete modeled assembly.
- Temperature difference
- Thermal driving force between the two modeled sides.
- Heat rate
- Thermal energy transferred per unit time.
- Heat flux
- Heat-transfer rate per unit area.
Important note
Calculated from the entered values using the displayed engineering relationship. Confirm design values, load cases, safety factors, standards, and field conditions with a qualified professional.
Frequently asked questions
Is a lower U-value better insulation?
Yes for the same boundary definition; lower U means less heat transfer per area and temperature difference.
Can delta T be negative?
A sign can indicate direction, but the calculator is mainly designed to report transfer magnitude from a nonnegative entered difference.
Is thermal kWh the same as electrical kWh?
No. Equipment efficiency or coefficient of performance relates purchased energy to delivered or removed heat.
Does the calculator include air leakage?
No. Infiltration and ventilation require airflow and air-property calculations.