Heat Transfer Calculator
Calculate steady-state heat transfer rate through a flat wall by conduction, or from a surface to a fluid by convection.
Enter your values
Choose mode, then fill in the fields below.
How this calculator works
For steady-state conduction through a flat wall (Fourier's law):
k is thermal conductivity of the wall material, A is the cross-sectional area perpendicular to heat flow, L is wall thickness, and ΔT is the temperature difference across the wall. For convection between a surface and a moving fluid (Newton's law of cooling):
h is the convective heat transfer coefficient (depends on fluid, flow velocity, and surface geometry), A is surface area, and ΔT is the temperature difference between surface and fluid.
Typical property values
| Material / condition | Typical value |
|---|---|
| Mild steel (k) | 45 – 60 W/m·K |
| Brick / masonry (k) | 0.6 – 1.0 W/m·K |
| Fiberglass insulation (k) | 0.035 – 0.045 W/m·K |
| Natural convection, air (h) | 5 – 25 W/m²·K |
| Forced convection, air (h) | 25 – 250 W/m²·K |
| Forced convection, water (h) | 500 – 10,000 W/m²·K |
Frequently asked questions
Can I use this for a multi-layer wall?
Not directly — for multiple layers in series, calculate each layer's thermal resistance (R = L/(k·A)) separately, sum the resistances, then divide the total ΔT by the summed resistance to get Q.
How do I find the convection coefficient, h, for my situation?
h depends on fluid properties, flow velocity, and geometry, and is normally obtained from correlations (e.g. Nusselt number relations) or reference tables for the specific flow condition — the typical ranges above are a starting estimate only.