Process Manufacturing calculator
Heat Exchanger Duty Calculator
Find the duty an exchanger must deliver for a process stream and whether it fits the exchanger's rating. You need the mass flow, specific heat, temperature change and margin.
What this calculator does
- Heat duty a single-phase stream needs, with the fouling margin, against the exchanger's duty rating.
Formula used
- Clean duty = mass flow × specific heat × temperature change
- Required duty = clean duty × fouling and design margin
- Fouling allowance = required − clean; heat capacity rate = mass flow × specific heat
- Duty share of rating = required ÷ rating × 100
Inputs explained
- Process Fluid Mass Flow: Process fluid mass flow, not the utility stream.
- Fluid Specific Heat: Fluid heat capacity per pound per degree F.
- Temperature Change: Rise or drop across the exchanger as a difference.
- Fouling and Design Margin: Multiplier covering dirt and design uncertainty on the clean duty.
- Exchanger Duty Rating: Rated duty from the exchanger nameplate or vendor data.
How to use the result
- Best suited to sizing an exchanger for a new duty, checking a fouled exchanger against rating, comparing the duty of two stream rates.
- A phase change or a variable specific heat needs a full heat curve, not one cp. The rating is a design duty; actual capacity falls with fouling and flow changes.
Current U.S. benchmarks
- The producer price index for industrial chemicals stands at 336.006 (BLS, Aug 2026), up 13.3% from a year earlier. Quotes priced off last quarter's material cost miss this move.
- The U.S. has 14,543 chemical manufacturing establishments employing about 911,245 workers (Census County Business Patterns, 2023).
Common questions
- What margin should I use for fouling? Many plants start near 1.15 for a clean service and 1.25 or more for a fouling stream. Check the exchanger's last cleaning date and the vendor's design margin.
- Why is temperature change entered in F and not C? A difference in F equals a difference in R, and the specific heat is on the same Fahrenheit basis. Enter the rise or drop as a difference, never an absolute reading.
- How do I get specific heat? From the fluid's data sheet or a heat capacity table at the average temperature. Water-like liquids run near 1 Btu/lb F; light oils run near 0.5.
- Does this size the exchanger area? No. This is the duty only. Sizing area needs the overall heat transfer coefficient and the mean temperature difference, which the exchanger vendor or a full thermal design provides.
Last reviewed 2026-10-01.