Heat Transfer Coefficient Converter
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| Unit | Equivalent Value |
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The Heat Transfer Coefficient (also known as the Convective Film Coefficient or Overall Thermal Transmittance U-Factor, symbolized by h or U) measures the rate of thermal energy transfer per unit surface area per unit temperature difference across a fluid boundary or multi-layer barrier (q'' = h · ΔT ⇒ h = q'' ÷ ΔT = P ÷ (A · ΔT)). Across HVAC building envelope window U-factor ratings, shell-and-tube heat exchanger sizing, electronic liquid cold plate design, boiler steam condensation, and re-entry spacecraft thermal shields, the heat transfer coefficient is categorized across three major engineering unit families: International System of Units (SI metric fundamental: Watt per Square Meter Kelvin / W/(m2·K), Watt per Square Meter °C / W/(m2·°C), Joule per Second Sq. Meter Kelvin / J/(s·m2·K)), Imperial / US Customary standards (Btu per Hour Sq. Foot °F / Btu/(h·ft2·°F), Btu per Second Sq. Foot °F / Btu/(s·ft2·°F), Centigrade Heat Units per Hour Sq. Foot °C / CHU/(h·ft2·°C)), and CGS laboratory metrics (Calorie per Second Sq. Centimeter °C / cal/(s·cm2·°C), Kilocalorie per Hour Sq. Meter °C / kcal/(h·m2·°C)).
Our free online Heat Transfer Coefficient Converter provides instant, high-precision conversions across all SI metric, Imperial HVAC U-factor, heat exchanger, and phase change convection units:
- Btu (IT) per Hour Sq. Foot °F to W/(m2·K) [Building Window U-Factor]: Multiply Btu/(h·ft2·°F) by
5.67826334(1 Btu/(h·ft2·°F) = 5.67826 W/(m2·K) = 4.88243 kcal/(h·m2·°C)). - Watt per Square Meter Kelvin to Btu/(h·ft2·°F): Multiply W/(m2·K) by
0.17611018(1 W/(m2·K) = 0.17611 Btu/(h·ft2·°F) = 0.85985 kcal/(h·m2·°C)). - Kilocalorie (IT) per Hour Sq. Meter °C to W/(m2·K): Multiply kcal/(h·m2·°C) by
1.1630(1 kcal/(h·m2·°C) = 1.1630 W/(m2·K) = 0.20482 Btu/(h·ft2·°F)). - Calorie (IT) per Second Sq. Centimeter °C to W/(m2·K): Multiply by
41,868.0(1 cal/(s·cm2·°C) = 41,868 W/(m2·K) = 7,373.38 Btu/(h·ft2·°F)). - Btu (IT) per Second Sq. Foot °F to W/(m2·K): Multiply by
20,441.748(1 Btu/(s·ft2·°F) = 20,441.75 W/(m2·K) = 3,600.0 Btu/(h·ft2·°F)). - CHU per Hour Sq. Foot °C to W/(m2·K):
1 CHU/(h·ft2·°C) = 5.678263 W/(m2·K)(1:1 identical to Btu/(h·ft2·°F)).
Master Heat Transfer Coefficient & U-Factor Conversion Table
The table below displays exact mathematical conversion relationships, SI W/(m2·K) multipliers, and imperial Btu/(h·ft2·°F) equivalents relative to 1 Watt per Square Meter Kelvin (1 W/(m2·K) = 1 W/(m2·°C)):
| Heat Transfer Coefficient Unit Name | Symbol | Exact Value in W/(m2·K) | Btu/(h·ft2·°F) & kcal Equivalent | Domain & Technical Application Standard |
|---|---|---|---|---|
| 1 Watt per Square Meter Kelvin | W/(m2·K), W/(m2·°C) |
1.0 W/(m2·K) (Base SI Unit) |
0.176110 Btu/(h·ft2·°F) (0.859845 kcal/(h·m2·°C) / 1.0 J/(s·m2·K)) |
SI Fundamental Heat Transfer Coefficient Standard |
| 1 Btu (IT) per Hour Sq. Foot °F | Btu/(h·ft2·°F), U-factor |
5.678263 W/(m2·K) |
1.0 Btu/(h·ft2·°F) (4.88243 kcal/(h·m2·°C)) |
US Imperial Building Window U-Factor & HVAC Standard |
| 1 Kilocalorie (IT) per Hour Sq. Meter °C | kcal/(h·m2·°C) |
1.163000 W/(m2·K) |
0.204816 Btu/(h·ft2·°F) (1.1630 J/(s·m2·K)) | European Building HVAC & Insulation Rating |
| 1 Kilocalorie (IT) per Hour Sq. Foot °C | kcal/(h·ft2·°C) |
12.518428 W/(m2·K) |
2.20462 Btu/(h·ft2·°F) (10.7639 kcal/(h·m2·°C)) | Mixed Metric/Imperial Thermal Transmittance |
| 1 Calorie (IT) per Second Sq. Centimeter °C | cal/(s·cm2·°C) |
41,868.0 W/(m2·K) |
7,373.38 Btu/(h·ft2·°F) (36,000.0 kcal/(h·m2·°C)) | Laboratory Physics & Ultra-High Convection |
| 1 Btu (IT) per Second Sq. Foot °F | Btu/(s·ft2·°F) |
20,441.75 W/(m2·K) |
3,600.0 Btu/(h·ft2·°F) (17,576.8 kcal/(h·m2·°C)) | Transient Rocket Engine & Gas Turbine Convection |
| 1 CHU per Hour Sq. Foot °C | CHU/(h·ft2·°C) |
5.678263 W/(m2·K) |
1.0 Btu/(h·ft2·°F) (4.88243 kcal/(h·m2·°C)) | Historical British Power Plant Heat Transmittance |
Step-by-Step Building Window U-Factor & Heat Loss Calculation Example
To convert an energy-efficient double-pane Low-E window with an overall U-factor of 0.25 Btu per Hour Sq. Foot °F (U = 0.25 Btu/(h·ft2·°F)) into SI metric W/(m2·K) and calculate heat loss (Q) through a 10 m2 glass facade when indoor temperature is 20°C and outdoor temperature is -10°C (ΔT = 30 K = 54°F):
Step 1 (SI Metric U-Factor Conversion): U = 0.25 × 5.6782633 = 1.41957 W/(m2·K) (1.42 W/(m2·K))
Step 2 (Metric Facade Heat Flow Q): Q = U · A · ΔT = 1.41957 W/(m2·K) × 10 m2 × 30 K = 425.87 Watts (425.9 W)
Step 3 (Imperial Verification): Q = 0.25 Btu/(h·ft2·°F) × 107.639 ft2 × 54°F = 1,453.13 Btu/h = 425.87 Watts
Thus, the Low-E window has a metric U-factor of 1.42 W/(m2·K), losing 425.9 Watts of heat through the 10 m2 facade across a 30°C winter temperature drop.
Real-World Convective & Overall U-Factor Benchmarks
Below is a comparative reference chart showing convective film coefficients (h) and overall U-factors across air, liquid cooling, boiling, steam, and insulated windows:
| Convective Fluid Boundary / Building Barrier | Heat Transfer Coefficient in SI (W/(m2·K)) | Imperial U-Factor Equivalent (Btu/(h·ft2·°F)) | Thermal Engineering & HVAC Physics Context |
|---|---|---|---|
| Stagnant Air Free Natural Convection (Vertical Wall) | 2.0 – 10.0 W/(m2·K) | 0.35 – 1.76 Btu/(h·ft2·°F) | Unassisted air natural convection boundary layer |
| Single-Pane Glass Window Overall U-Factor | 5.70 W/(m2·K) | 1.004 Btu/(h·ft2·°F) | Uninsulated single-pane glass thermal transmittance |
| Double-Pane Argon Low-E Window Overall U-Factor | 1.40 W/(m2·K) | 0.247 Btu/(h·ft2·°F) | High-efficiency residential insulated window U-factor |
| Forced Air Convection (HVAC Duct & Computer Fan) | 10.0 – 100.0 W/(m2·K) | 1.76 – 17.61 Btu/(h·ft2·°F) | Fan-driven forced air heat sink fin cooling |
| Forced Water Flow (Hydronic Loops & CPU Cold Plate) | 500.0 – 10,000.0 W/(m2·K) | 88.06 – 1,761.10 Btu/(h·ft2·°F) | High-performance liquid cooling heat exchanger film |
| Boiling Water Pool Nucleate Phase Change | 2,500.0 – 35,000.0 W/(m2·K) | 440.28 – 6,163.86 Btu/(h·ft2·°F) | Phase change boiling in power station steam generators |
| Condensing Pure Steam (Shell-and-Tube Condensers) | 5,000.0 – 100,000.0 W/(m2·K) | 880.55 – 17,611.0 Btu/(h·ft2·°F) | Extreme filmwise & dropwise steam condensation heat transfer |
History & Physics: 1701 Isaac Newton Law of Cooling vs Overall U-Factor (U = 1 ÷ Rtotal)
1701 Sir Isaac Newton & Law of Cooling (q” = h · ΔT)
In 1701, Sir Isaac Newton published Scala Graduum Caloris, formulating Newton’s Law of Cooling: convective heat transfer rate is directly proportional to the temperature difference between a solid surface and a surrounding fluid (q'' = h · (Ts - T&infty;)). Newton established the fundamental physical concept of the convective heat transfer coefficient (h) in W/(m2·K).
Overall U-Factor vs Total Insulation R-Value (U = 1 ÷ Rtotal)
In modern architectural building physics, overall thermal performance is defined by the U-Factor (U = 1 ÷ Rtotal). The total thermal resistance (Rtotal) sums interior convective film resistance (1 ÷ hi), conduction resistance across all material layers (Σ (L ÷ k)), and exterior convective film resistance (1 ÷ ho). Computing U = 1 ÷ Rtotal allows engineers to convert layer thermal properties directly into overall heat loss ratings.
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Frequently Asked Questions (FAQ)
How do you convert W/(m2·K) to Btu/(h·ft2·°F)?
To convert Heat Transfer Coefficient from W/(m2·K) to Btu/(h·ft2·°F), multiply by 0.176110 (or divide by 5.678263). For example, 100 W/(m2·K) forced air convection × 0.176110 = 17.61 Btu/(h·ft2·°F).
How do you convert a window U-factor from Btu/(h·ft2·°F) to W/(m2·K)?
To convert a window U-factor from Imperial Btu/(h·ft2·°F) to SI W/(m2·K), multiply by 5.678263. For example, a window with U = 0.30 Btu/(h·ft2·°F) × 5.678263 = 1.70 W/(m2·K).
What is the difference between Heat Transfer Coefficient (h) and Thermal Conductivity (k)?
Thermal Conductivity (k in W/(m·K)) is an intrinsic material property measuring heat conduction through a solid barrier. Heat Transfer Coefficient (h in W/(m2·K)) is a boundary surface property measuring convective heat transport between a solid wall and moving fluid.
What is the relationship between U-Factor and R-Value?
The U-Factor and R-Value are mathematical reciprocals: U = 1 ÷ R (in Imperial units, U = 1 ÷ RIP; in SI units, USI = 1 ÷ RSI). A higher R-value means better insulation, whereas a lower U-factor means lower heat loss.