# Overall Heat Transfer Coefficient (1/U=ΣR) Compute the overall heat transfer coefficient for series thermal resistances (flat-wall model): total resistance R_total = Σ R_i (K/W), thermal conductance G = 1/R_total (W/K), area-based coefficient U = 1/(R_total·A) (W/(m²·K)), and if a temperature difference is given the heat flow rate Q = ΔT/R_total (W). Each R_i is a layer resistance already containing the area factor (e.g. convection R_conv=1/(h·A), conduction R_cond=d/(k·A), fouling R_foul=R_f''/A). Enter one resistance (K/W) per line, at least one, all positive. ΔT may be negative (reverse heat flow); a °C difference equals a K difference, a °F difference is converted by ×5/9. > Canonical page: https://elysiatools.com/en/tools/overall-heat-transfer-coefficient - **Category:** Math & Numbers - **Keywords:** overall heat transfer coefficient, U-value, thermal resistance, series resistance, heat transfer, 1/U=ΣR, thermal conductance, heat flow rate, convection resistance, conduction resistance, fouling resistance, R_total, heat exchanger, wall, composite wall, insulation ## Overview Calculate the overall heat transfer coefficient for thermal resistances in series. Enter one positive resistance per line to find total resistance, thermal conductance, and area-based U-value; optionally add a temperature difference to calculate heat flow rate. ## Inputs - **Series Resistances (K/W)** (textarea): One thermal resistance per line (K/W), already containing the area factor (e.g. R_conv=1/(h·A), R_cond=d/(k·A), R_foul=R_f''/A). At least one positive value required. - **Heat Transfer Area A (m²)** (number): Heat transfer area A (m²) used to collapse R_total to the area-based overall coefficient U = 1/(R_total·A). Must be positive. - **Temperature Difference ΔT (optional)** (number): Temperature difference ΔT across the resistance stack, in the selected Temperature Unit. If provided, the heat flow rate Q = ΔT/R_total is computed. May be negative to indicate the reverse heat-flow direction. - **Temperature Unit** (select): Unit of the temperature difference. This is a difference, not an absolute temperature: Δ°C = ΔK and Δ°F ×5/9 = ΔK. - **Decimal Places** (number) ## When to use - Estimate heat transfer through a flat wall made of multiple resistance layers. - Calculate U-values for composite walls, insulation, heat exchangers, or fouled surfaces. - Find heat flow from a known temperature difference across a series resistance stack. ## How it works - Enter one or more positive thermal resistances in K/W, with each value already containing its area factor. - Enter the heat transfer area in m²; the default area is 1 m². - Optionally enter ΔT and select K, °C, or °F. Fahrenheit differences are converted to kelvins. - The tool sums the resistances and returns R_total, G = 1/R_total, U = 1/(R_total·A), and, when ΔT is provided, Q = ΔT/R_total. ## Use cases - Analyze convection, conduction, and fouling resistances across a composite wall. - Compare insulation or wall designs using total resistance and U-value. - Estimate heat exchanger or wall heat flow when the temperature difference is known. ## Frequently asked questions ### What inputs does the calculator require? Enter at least one positive thermal resistance in K/W, with one value per line. ### What does the area input affect? Area is used to calculate the area-based coefficient U = 1/(R_total·A). ### Can I calculate heat flow rate? Yes. Enter ΔT to calculate Q = ΔT/R_total in watts. ### Can temperature difference be entered in Celsius or Fahrenheit? Yes. A Celsius difference equals the same kelvin difference, while a Fahrenheit difference is multiplied by 5/9. ### Can ΔT be negative? Yes. 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