Our heat flux density converter allows precise conversion between different units of thermal flow rate per unit area, including watts per square meter, kilocalories per hour per square meter, and BTU per hour per square foot.
Heat flux density is the rate of heat energy transfer through a surface per unit area. It quantifies how quickly thermal energy flows through a specific area and is a fundamental parameter in heat transfer analysis, thermal engineering, and building science. Heat flux density is measured perpendicular to the direction of heat flow.
Convert between different heat flux density units with our free online calculator. Perfect for engineering, scientific, and professional applications.
Common heat flux density conversions
| From | To | Context |
|---|---|---|
| 100 Watts Per Square Meter (W/m²) | 86.0000 Kilocalories Per Hour Square Meter (kcal/h·m²) | Typical solar radiation on a cloudy day |
| 10 Btu Per Hour Square Foot (BTU/h·ft²) | 31.5000 Watts Per Square Meter (W/m²) | Heat loss through a residential wall |
| 50 Kilocalories Per Hour Square Meter (kcal/h·m²) | 58.1400 Watts Per Square Meter (W/m²) | Heat transfer in a small heat exchanger |
Heat flux density measurements help determine how well building materials and assemblies resist heat flow, affecting energy efficiency.
Engineers use heat flux density calculations to design cooling systems for electronic components and prevent overheating.
Heat flux density is used to quantify solar radiation intensity for solar thermal and photovoltaic system design.
Heat flux density calculations are essential for designing heat exchangers, furnaces, and other thermal equipment.
Heat flux is the total rate of heat transfer (in watts or BTU/hour), while heat flux density is the rate of heat transfer per unit area (W/m² or BTU/h·ft²). Heat flux density allows for standardized comparison of heat transfer rates across different surface areas.
Heat flux density is typically measured using heat flux sensors (or heat flux meters) that generate an electrical signal proportional to the heat flow through them. It can also be calculated indirectly by measuring temperature gradients across materials with known thermal conductivity.
For a well-insulated residential wall in a temperate climate, heat flux density typically ranges from 5-15 W/m² (1.6-4.8 BTU/h·ft²) during winter. Poorly insulated walls may have values of 30-50 W/m² (9.5-15.8 BTU/h·ft²) or higher.
Heat flux density (q) through a building assembly is related to the temperature difference (ΔT) and the assembly's U-value by the equation: q = U × ΔT. Since R-value is the reciprocal of U-value, the relationship can also be expressed as: q = ΔT ÷ R.
The SI unit of heat flux density. It represents the rate of energy transfer of one watt through an area of one square meter.
A unit commonly used in some engineering applications, especially in regions that traditionally use the calorie. One kcal/h·m² equals approximately 1.163 W/m².
A unit commonly used in HVAC and building engineering in the United States. One BTU/h·ft² equals approximately 3.155 W/m².
| Application | Typical Heat Flux Density | Notes |
|---|---|---|
| Direct sunlight (noon, clear sky) | 800-1000 W/m² | Maximum solar radiation at Earth's surface |
| Well-insulated building wall (winter) | 5-15 W/m² | Depends on temperature difference and insulation |
| CPU heat sink | 10,000-100,000 W/m² | High-performance computing requires efficient cooling |
| Industrial boiler tubes | 20,000-70,000 W/m² | Varies with boiler type and operation |
| Human body (resting) | 40-60 W/m² | Total heat output divided by body surface area |
In building science, heat flux density is a critical parameter for evaluating thermal performance. It can be calculated using the equation:
Where:
This relationship is fundamental to building energy calculations and thermal design. Lower U-values (higher R-values) result in lower heat flux density, indicating better insulation performance.