Heat Exchanger Duty Calculator - Q, LMTD, UA Product & Approach
Calculate heat transfer duty, log mean temperature difference, and required surface area for shell-and-tube and plate exchangers
Enter hot-side and cold-side temperatures, flow rates, fluid placeholders, and counterflow or parallel-flow arrangement to calculate a steady-state screening result. The app reports hot-side duty, cold-side duty, average duty Q, LMTD, UA product, approach temperature, effectiveness, duty-balance warnings, and source pointers. It does not calculate exchanger surface area, U-value selection, fouling factors, correction factors, pressure drop, phase change, shell-and-tube geometry, TEMA design, ASME pressure-vessel compliance, or manufacturer rating.
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Heat Exchanger Basics Guide →How It Works
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Enter Measured Stream Conditions
Enter hot-side and cold-side inlet temperature, outlet temperature, and flow rate. The app assumes steady-state single-phase flow and constant local fluid properties.
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Select Fluid Placeholders
Choose water, 25% glycol, or 50% glycol for each side. Glycol rows are broad local placeholders and must be replaced by current product data for decision use.
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Choose Arrangement
Select counterflow or parallel flow. The app calculates only ideal terminal-temperature LMTD for these two arrangements and does not apply shell-pass, crossflow, or TEMA correction factors.
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Review Warnings First
Check temperature-cross, small-approach, high-effectiveness, and duty-imbalance warnings before using the Q, LMTD, UA product, or effectiveness values as an estimate.
Built For
- Plant teams checking whether measured hot-side and cold-side duties are in the same range before deeper troubleshooting
- Maintenance planners preparing exchanger trend notes for engineering review
- Process and facilities engineers doing an initial steady-state heat-duty screen before manufacturer or thermal-rating work
- HVAC and hydronic technicians estimating water or glycol-side duty while keeping product-data and pump-effect caveats visible
- Energy auditors documenting preliminary heat-recovery opportunities without treating the app as final design software
Features & Capabilities
Two-Sided Duty Check
Calculates hot-side and cold-side duty from local density, Cp, flow, and temperature change, then reports the duty balance as a warning path.
Ideal LMTD Calculator
Calculates LMTD for counterflow and parallel-flow terminal temperatures only, with warnings for zero or negative terminal driving force.
UA Product Output
Reports Qavg divided by LMTD as a UA product. The app does not split U from area A or select either value.
Source Boundary Export
Reports and PDF exports carry ASHRAE, TEMA, ASME, and glycol-product source pointers plus explicit limits for design, pressure, fouling, and manufacturer decisions.
Comparison
| Area | Included in App | Requires External Review |
|---|---|---|
| Thermal duty | Q from local flow, density, Cp, and temperature change | Instrument accuracy, phase behavior, heat loss, current fluid properties |
| Temperature driving force | Ideal counterflow or parallel-flow LMTD | Crossflow, shell-pass, multipass, or correction-factor methods |
| UA product | Qavg divided by LMTD | Separate U-value, surface area, fouling, geometry, and manufacturer rating |
| Fluid rows | Water plus broad 25% and 50% glycol placeholders | Current product data, concentration test, viscosity, pump head, SDS, compatibility |
| Safety and code | Source warnings and citations | TEMA, ASME BPVC, API, relief, inspection, repair, AHJ, and qualified review |
Assumptions
- Steady-state single-phase liquid streams with constant flow rates and terminal temperatures.
- Local constant Cp and density rows are used for water and glycol placeholders.
- Average duty is the arithmetic average of hot-side and cold-side duty.
- LMTD is ideal counterflow or parallel flow only; no correction factor is applied.
- UA is reported as a product and is not split into U and area A.
Limitations
- Does not calculate exchanger type, surface area, U-value, fouling factors, pressure drop, Reynolds number, viscosity effects, or pump impact.
- Does not model condensers, evaporators, reboilers, two-phase flow, phase change, flashing, boiling, or steam quality.
- Does not perform shell-and-tube geometry, baffle, vibration, nozzle-load, metallurgy, corrosion, relief, pressure-boundary, or inspection checks.
- Does not determine cleaning interval, repair method, purchase acceptance, manufacturer rating, TEMA/API/ASME compliance, or AHJ approval.
References
- ASHRAE Handbook source pointers for heat-transfer equations and current fundamentals context.
- TEMA Standards Eleventh Edition source pointer for shell-and-tube exchanger standards context.
- ASME BPVC Section VIII Division 1 source pointer for pressure-vessel scope and boundaries.
- Dow DOWFROST and DOWTHERM SR-1 source pointers for glycol product-data context.