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.
Calculate pipe pressure drop through exchanger piping
Pipe Pressure Drop Calculator →Look up steam tables for condensing services
Steam Properties Calculator →Review pump speed and impeller prompts separately
Pump Affinity Laws Calculator →Read heat exchanger screening basics
Heat Exchanger Basics Guide →How It Works
-
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.
-
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.
-
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.
-
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.
Frequently Asked Questions
Learn More
Heat Exchanger Basics: LMTD, UA, Fouling & Approach Temperature
Understanding heat exchanger duty calculations: LMTD method, UA rating, fouling factors, approach temperature, and when to clean or replace exchangers.
Mechanical Insulation Thickness Source Boundaries
How to calculate insulation thickness using ASTM C680 method. Heat loss, surface temperature, condensation prevention, and material selection for pipes and equipment.
Steam Properties and Boiler Operations Guide
How to use steam tables for steam trap sizing, boiler efficiency calculations, flash steam recovery, deaerator verification, and superheated steam applications. Covers hf, hfg, hg, and specific volume.
Related Tools
Shop Heater BTU Sizing Calculator
Calculate the exact BTU output your shop or garage heater needs. Factors in wall R-values, ceiling insulation, slab edge loss, overhead door infiltration, and air changes per hour to size propane, natural gas, and electric heaters correctly.
Overhead Door Infiltration Loss Calculator
Calculate heat loss through overhead doors in shops, garages, and warehouses. Compares open-door vs closed-door losses, seal condition impact, and annual cost of infiltration with payback on door seals and high-speed doors.
Long-Run Voltage Drop Calculator
Calculate voltage drop for long wire runs to detached shops, barns, garages, and outbuildings. Compares copper vs aluminum, shows motor starting voltage impact, and recommends the right wire size for your distance and load.