IES
Thermal Engineering2D

Heat Transfer Calculator

Calculate heat transfer rate Q through a wall or surface using the conductive/convective heat transfer equation.

Inputs
Enter your values below

Air free convection: 5-25; forced air: 25-250; liquid: 100-1000

Result
Heat Transfer Rate
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Enter values and click Calculate
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Formula
u × area × delta_t
Result unit: W

Q = U × A × ΔT. Heat transfer rate equals overall heat transfer coefficient × area × temperature difference. U in W/(m²·K), A in m², ΔT in K.

Introduction

The fundamental heat transfer equation Q = U·A·ΔT calculates heat flow across a surface or through a composite wall. U (overall heat transfer coefficient) combines convection on both sides and conduction through the material.

How This Calculator Works

Q = U × A × ΔT. Heat transfer rate equals overall heat transfer coefficient × area × temperature difference. U in W/(m²·K), A in m², ΔT in K.

Step-by-step process:

  1. Enter your input values in the calculator above
  2. The engine converts all inputs to SI base units (meters, kg, Pa)
  3. The formula is evaluated: u * area * delta_t
  4. Result is formatted with the appropriate unit and precision

Calculation Example

A 10 m² wall with U=25 W/m²K across 20°C ΔT loses 5,000 W (5 kW).

Inputs: u=25, area=10, delta_t=20
Result: 5000 W

Unit Conversion for Heat Transfer

**Heat rate units**

- 1 W = 3.412 BTU/hr = 0.860 kcal/h

- 1 kW = 3412 BTU/hr

- 1 BTU/hr = 0.2931 W

**Temperature units**

- °F = °C × 9/5 + 32

- ΔT in °C = ΔT in K; ΔT in °F = ΔT in °R

**Area units**

- 1 m² = 10.764 ft²

Heat transfer Q = U × A × ΔT requires consistent units. Convert area, temperature difference, and U-value to one unit system before computing.

Engineering Applications

  • •Building heat loss
  • •Heat exchanger rating
  • •Insulation design
  • •HVAC load calc

Frequently Asked Questions

What is a typical U-value?

Insulated building wall: 0.2-0.5 W/m²K; uninsulated brick wall: 2-3; window single pane: ~5; forced-air heat exchanger: 25-100; shell-and-tube liquid-liquid: 300-1000.

How do I calculate U from k (conductivity)?

For a flat wall: U = k/L (conductivity/thickness). For composite walls: U = 1/Σ(L_i/k_i) including convection resistances on each side.

How do I convert heat transfer rate between W and BTU/hr?

1 W = 3.412 BTU/hr. For example, 1000 W = 3412 BTU/hr. Conversely, divide BTU/hr by 3.412 to get W.

Related Calculators

Heat Exchanger Calculator (LMTD Method)LMTD Calculator - Log Mean Temperature DifferenceHeat Loss Calculator - Pipe & Tank Insulation

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Engineering Disclaimer: Calculations are for reference and educational purposes only. Always verify results independently for engineering design. See full disclaimer.
Reviewed by: Industrial Engineering Team
References: ASME B31.3, ASTM A36, Perry's Chemical Engineers' Handbook