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Heat Exchanger LMTD & UA Calculator

Calculate counter-current LMTD and required UA from temperatures and heat duty.

Updated September 2026

How it works

Calculate counter-current LMTD and required UA from temperatures and heat duty.

Formula:
ΔT1 = Thi−Tco; ΔT2 = Tho−Tci; LMTD = (ΔT1−ΔT2)/ln(ΔT1/ΔT2); UA = Q/LMTD.

Before you use the result: Temperature cross, phase change, fouling and correction factors may require more detailed design.

Practical use

Use verified material data and project geometry. Treat results as planning estimates and compare them with the energy/thermal requirements that apply to the project.

Keep units consistent with the source information.
Use project-specific densities, pack sizes and coverage rates where provided.
Round purchasing quantities to supplier packaging and delivery rules.

How to use this calculator: Heat Exchanger LMTD & UA Calculator

Calculate counter-current LMTD and required UA from temperatures and heat duty.

Quick workflow

Enter the project values from the latest drawing, specification or verified site measurement.
Check units, material properties, allowances and any code- or supplier-specific parameters before calculating.
Review the result together with the formula, assumptions and the related checks shown on this page.

Worked example

Example inputs: Hot inlet [°C]: 80; Hot outlet [°C]: 55; Cold inlet [°C]: 20; Cold outlet [°C]: 45.

Using the sample values built into the calculator, the calculation gives approximately: Log mean temperature difference: 35 K; Required UA: 3.429 kW/K.

What the result means

Calculation method: ΔT1 = Thi−Tco; ΔT2 = Tho−Tci; LMTD = (ΔT1−ΔT2)/ln(ΔT1/ΔT2); UA = Q/LMTD.

Before using the result: Temperature cross, phase change, fouling and correction factors may require more detailed design.

Common questions

What does this calculator do?

Calculate counter-current LMTD and required UA from temperatures and heat duty.

Which inputs should I verify?

Key inputs to verify include: Hot inlet [°C], Hot outlet [°C], Cold inlet [°C], Cold outlet [°C].

Can I use this result for final design or ordering?

Use the result as a transparent planning or checking aid. Final design, code compliance, supplier selection and project-specific decisions still need to be verified where applicable. Temperature cross, phase change, fouling and correction factors may require more detailed design.

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