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Heat Transfer Calculator

Calculate heat transfer rate through a barrier from area, temperature difference and U-value.

About Heat Transfer Calculator

Heat flow is proportional to area, temperature difference and the U-value. Since U is the reciprocal of thermal resistance, halving U halves the heat loss for the same conditions. Building regulations specify maximum U-values precisely because this equation makes heat loss directly proportional to them.

Formula

Heat Transfer

Q̇ = U A ΔT

U
Overall heat transfer coefficient, the reciprocal of thermal resistance
ΔT
Temperature difference across the barrier

Worked example

With the default values below, Heat Transfer Calculator returns Heat Transfer Rate of 120.000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Surface areaminimum 0 m2
20 m2
Overall heat transfer coefficientminimum 0.001 W/m2 K
0.3 W/m2 K
Temperature differenceminimum 0 K
20 K
Hours per dayaccepts 0–24 h
24 h

Results

Heat Transfer Rate
120.000 W
Daily Energy Transferred
2.8800 kWh
Annual Energy Transferred
1,051.2 kWh
Heat Flux per Square Metre
6.000 W/m2
Thermal Resistance
3.3333 m2 K/W

Step by step

  1. 1Values used
  2. 2Heat Transfer
  3. 3Heat Transfer Rate= 120.000 W
  4. 4Daily Energy Transferred= 2.8800 kWh
  5. 5Annual Energy Transferred= 1,051.2 kWh
  6. 6Heat Flux per Square Metre= 6.000 W/m2
  7. 7Thermal Resistance= 3.3333 m2 K/W

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Heat Transfer calculated?

Q̇ = U A ΔT Heat flow is proportional to area, temperature difference and the U-value. Since U is the reciprocal of thermal resistance, halving U halves the heat loss for the same conditions.

Why does Heat Transfer matter?

Building regulations specify maximum U-values precisely because this equation makes heat loss directly proportional to them.

What values do I need to enter?

This calculator takes 4 inputs: Surface area, Overall heat transfer coefficient, Temperature difference, Hours per day. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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