Heat Transfer and Thermal Calculators
These calculators cover heat in buildings, machines and processes: how much heat escapes through a wall or roof build-up and what its U-value is, how much a steel pipe or aluminium rail grows when it warms up, how much energy it takes to heat a mass of material, the log mean temperature difference that sizes a heat exchanger, and how long a heater takes to bring a tank of water to temperature.
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All Thermal (5)
Heat Loss Calculator
Conduction heat loss and U-value through walls and insulation layersThermal Expansion Calculator
Linear and volumetric expansion of materials with temperatureSpecific Heat Calculator
Heat energy to raise or lower a material's temperatureHeat Exchanger LMTD Calculator
Log mean temperature difference and duty for heat exchangersWater Heating Time Calculator
Time and energy to heat water with a given heater power
Which tool do I need?
Compare the heat loss of two wall insulation options
Build each wall from layers to get its R-value, U-value and the heat lost for your temperature difference.
Allow for expansion in a long pipe run
Enter the length, material and temperature change to see how much the pipe grows.
Work out how long a water heater takes to recover
Enter the volume, start and target temperatures and heater power to get the heating time and energy.
About Thermal
Material properties such as conductivity, expansion coefficients and specific heats are typical published values that you can edit. The formulas assume steady-state conduction, constant properties and no phase change unless the tool says otherwise.
Results are for checking, learning and preliminary design. Anything that carries load, current, pressure or people must be confirmed by a qualified engineer or licensed tradesperson against the code that governs your project.
Guides
- U-Value, R-Value and Heat Loss: Calculating a Wall Layer by LayerWhy thermal resistances add in series, where the ISO 6946 and ASHRAE surface films come from, how to convert R-13 to RSI, and what clear-field U-values leave out.
- Thermal Expansion in Pipes and Structures: ΔL = αLΔT in PracticeLinear and volumetric expansion explained, typical coefficients for steel, copper and plastics, why restrained members build stress, and how water breaks the simple rule.
- Specific Heat and Latent Heat Explained: Q = mcΔT and the Heating CurveWhat specific heat measures, where the calorie and BTU come from, why boiling takes five times the energy of heating, and how to solve calorimetry problems without unit slips.
- LMTD and the F Correction Factor: Sizing Heat ExchangersWhere the log mean temperature difference comes from, why counterflow beats parallel flow, how the shell-and-tube F factor is calculated and when F gets too low to trust.
Frequently asked questions
Should I compare walls by R-value or U-value?
R-value is resistance to heat flow and adds up layer by layer. U-value is its inverse for the whole build-up, the heat flow per unit area per degree of temperature difference. Lower U means better insulation.
Why use a log mean temperature difference instead of a simple average?
The temperature difference between the fluids changes along a heat exchanger, and heat transfer follows that changing difference exponentially. The log mean gives the exact average for that profile.
How much should I allow for steel pipe to grow when it heats up?
About 12 millionths of its length per degree Celsius, so a 10 m steel pipe grows about 6 mm when it warms by 50°C. Aluminium expands roughly twice as much.
Does the heat loss calculator include air leakage and thermal bridges?
No. It calculates conduction through the layers you enter. Air leakage, studs and other thermal bridges add to real losses, so whole-building calculations add allowances for them.