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Heat Transfer Coefficient Calculator

Calculate U-value and R-value for thermal analysis
Enter an R-value to calculate the corresponding U-value. U = 1/R

Enter values to calculate heat transfer coefficient.

Heat Transfer Guide

Understanding U-value and R-value

U-value and R-value are measures of thermal performance used in building insulation and HVAC design.

U-value (Heat Transfer Coefficient):
  • Definition: Rate of heat transfer through a material per unit area per degree temperature difference
  • Units: W/m²·K (metric) or BTU/hr·ft²·°F (imperial)
  • Lower is better: Lower U-value = better insulation
  • Formula: U = 1/R
R-value (Thermal Resistance):
  • Definition: Resistance to heat flow through a material
  • Units: m²·K/W (metric) or hr·ft²·°F/BTU (imperial)
  • Higher is better: Higher R-value = better insulation
  • Formula: R = thickness / thermal conductivity
Common R-values:
  • Fiberglass batt (3.5"): R-11 to R-13
  • Fiberglass batt (6"): R-19 to R-21
  • Spray foam (1"): R-6 to R-7
  • Rigid foam board (1"): R-4 to R-6

Applications

  • Building Design: Wall, roof, floor insulation
  • HVAC: Energy load calculations
  • Windows: Glazing performance
  • Energy Codes: Building code compliance
Pro Tips
  • Relationship
    U and R are reciprocals: U = 1/R. Lower U = Higher R = Better insulation.
  • Add R-values
    R-values add in series. Total R = R₁ + R₂ + R₃...
  • Surface Resistance
    Don't forget interior and exterior surface resistances!
Typical U-values
  • Single-pane window: 5.8 W/m²·K
  • Double-pane window: 2.8 W/m²·K
  • Insulated wall: 0.3-0.5 W/m²·K
  • Insulated roof: 0.2-0.3 W/m²·K

Frequently Asked Questions

Q: What's the difference between U-value and R-value?

A: U-value measures heat transfer rate (lower is better for insulation), while R-value measures thermal resistance (higher is better). They're reciprocals: U = 1/R. For example, R-20 insulation has U = 1/20 = 0.05 BTU/hr·ft²·°F.

Q: How do I calculate total R-value for a wall?

A: Add the R-values of all layers in series: Total R = R(interior surface) + R(drywall) + R(insulation) + R(sheathing) + R(siding) + R(exterior surface). Use our layer-by-layer calculator for automatic calculation including surface resistances.

Q: What R-value do I need for my climate?

A: It varies by location and building code. US recommendations: Walls R-13 to R-21, Attics R-30 to R-60, Floors R-13 to R-30. Colder climates need higher R-values. Check local building codes for specific requirements.

Q: What are surface resistances?

A: Surface resistances account for the thin air films on interior and exterior surfaces. Typical values: Interior surface R-0.68 (imperial) or 0.13 (metric), Exterior surface R-0.17 (imperial) or 0.04 (metric). Our calculator includes these automatically in layer mode.

Q: How do I convert between metric and imperial?

A: For U-value: 1 W/m²·K = 0.176110 BTU/hr·ft²·°F. For R-value: 1 m²·K/W = 5.678263 hr·ft²·°F/BTU. Our calculator automatically converts between both systems.

Q: Does R-value change with temperature?

A: Yes, thermal conductivity (and thus R-value) can vary with temperature. Most published R-values are at standard conditions (75°F/24°C). For extreme temperatures or precision work, use temperature-specific thermal conductivity values.

Disclaimer

Important Notice:

  • This calculator provides theoretical calculations based on standard formulas (U = 1/R, R = thickness/conductivity).
  • Actual thermal performance depends on many factors: installation quality, air leakage, thermal bridging, moisture, temperature, and aging.
  • Surface resistances used in layer mode are typical values. Actual values vary with surface orientation, air movement, and emissivity.
  • For building code compliance, verify calculations with local authorities and use certified materials with tested R-values.
  • Thermal bridging (studs, joists) reduces effective R-value. Use whole-wall R-value calculations for accurate energy modeling.
  • Material properties (thermal conductivity) can vary by manufacturer, density, moisture content, and temperature. Use manufacturer data when available.
  • This tool is for preliminary design and education. For professional building design, energy modeling, or code compliance, consult qualified engineers.
  • Energy calculations require more than just U-values: consider climate, orientation, air changes, internal gains, and HVAC efficiency.
  • We are not responsible for any errors, energy performance issues, code violations, or other consequences resulting from the use of this calculator.

Always verify calculations with qualified professionals and follow local building codes and energy standards.

Heat Transfer Calculator

Calculate U-value and R-value for thermal analysis. Two modes: simple R-to-U conversion or detailed layer-by-layer calculation!

Calculator Modes
R-to-U Conversion:

Quick conversion between R-value and U-value using U = 1/R

Layer-by-Layer:

Calculate from material properties (thickness & conductivity). Includes surface resistances.

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Heat Transfer & Insulation:

Did You Know?

The R-value concept was developed in the 1940s. Before that, insulation was often measured by thickness alone, which didn't account for material differences!