Heat Transfer Coefficient Converter

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)):

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:

History & Physics: 1701 Isaac Newton Law of Cooling vs Overall U-Factor (U = 1 ÷ R_total)

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 ÷ R_total)

In modern architectural building physics, overall thermal performance is defined by the U-Factor (U = 1 ÷ R_total). 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.

Popular direct tools:

• Conversion Calculator Main Directory
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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.