Sizes a counterflow heat exchanger both ways: Rating takes duty and the four terminal temperatures to the required UA (LMTD method); Performance takes UA and both flows to predicted outlet temperatures (effectiveness-NTU method).
Tender-stage sizing only. Verify against manufacturer selection software.
For design guidance only. Always verify against manufacturer selection software.
About this heat exchanger sizing calculator
This free heat exchanger sizing calculator solves the counterflow heat-exchanger problem both ways. In Rating mode it takes the duty and the four terminal temperatures and returns the counterflow LMTD and the required UA. In Performance mode it takes a UA and both stream flows and predicts the outlet temperatures using the effectiveness–NTU method. Water and ethylene/propylene glycol mixes are handled, with the specific heat auto-filled from Ensign’s glycol property tables. It is aimed at UK M&E and building services engineers sizing plate and shell-and-tube exchangers at tender stage. Everything runs in your browser. Nothing is uploaded.
How the heat exchanger is sized
Rating uses the log mean temperature difference: LMTD = (ΔT₁ − ΔT₂) ÷ ln(ΔT₁ ÷ ΔT₂) across the two end differences, then UA = Q ÷ (F × LMTD), where F is the flow-arrangement correction factor (1 for true counterflow). Performance uses the effectiveness–NTU relation for a counterflow exchanger, ε = (1 − e−NTU(1−Cr)) ÷ (1 − Cr·e−NTU(1−Cr)), with the Cr = 1 special case ε = NTU ÷ (1 + NTU), where NTU = UA ÷ Cmin and Cr = Cmin ÷ Cmax; the duty is then q = ε × Cmin × (Th,in − Tc,in). The two modes are the same underlying model, so a rating UA feeds straight into a performance check.
Frequently asked questions
What is the correction factor F?
F adjusts the counterflow LMTD for real flow arrangements. For a true counterflow exchanger F = 1 (the default). For multi-pass or cross-flow geometries F is less than 1 and is read from the standard F-charts for that configuration; enter it here so the required UA reflects the reduced effective mean temperature difference.
When do I use Rating versus Performance mode?
Use Rating when you know the duty and the required temperatures and want the UA needed to achieve them, the classic selection sum. Use Performance when you already have a UA (a rating result, or a datasheet figure) and want to predict how the exchanger behaves off-design, i.e. the outlet temperatures for given flows and inlets.
Can I use a glycol mix?
Yes. Select ethylene or propylene glycol for either stream and enter the concentration; the specific heat is interpolated from Ensign’s glycol property tables (0–60% by volume) and auto-filled, and you can override it with a datasheet value. A lower cp reduces the capacity rate, which changes both the NTU and the predicted duty.