Calculate heat duty (BTU/hr), LMTD, and required surface area (ft²) for shell & tube and plate heat exchangers. Built for U.S. manufacturing and process plants — with live flow diagrams and temperature charts.
Selects default overall heat transfer coefficient (U). Override below if needed.
Hot Side (Shell Side)
°F
°F
GPMgal/min
🧪
Cold Side (Tube Side)
°F
°F
🧪
Design Parameters
Counter-current is more efficient — always prefer unless process requires co-current.
0%10%20%30%
10–20% for cooling-tower water; 25–30% for untreated water or oils.
UBTU/hr·ft²·°F
Results
Heat Duty (Q)
—
BTU/hr
LMTD
—
log mean temp diff
Required Area (clean)
—
ft²
Design Area (w/ fouling)
—
ft²
U-Value Used
—
BTU/hr·ft²·°F
Cold Side Heat Gain
—
BTU/hr check
Sizing NoteEnter values and click Calculate.
Detailed Summary
Heat Duty
Heat duty Q (hot side)
—
Cold side check Q
—
Energy balance error
—
Temperature Analysis
ΔT₁
—
ΔT₂
—
LMTD
—
Flow arrangement
—
Heat Transfer Area
U-value (overall)
—
Clean area (A = Q/U·LMTD)
—
Fouling allowance
—
Design area (with fouling)
—
TEMA Shell Guidance
Approx. shell diameter
—
Recommended tube length
—
Inputs Used
HX type
—
Hot side
—
Cold side
—
Hot side flow
—
Live Flow Diagram — Updates With Your Inputs
Hot fluid (shell side)
Cold fluid (tube side)
Baffles
LMTD = driving force
Arrows show flow direction. Toggle Counter/Co-Current above to see the difference in the diagram.
Temperature Profile Along Exchanger Length
Hot fluid temperature
Cold fluid temperature
ΔT gap (LMTD driving force)
The shaded amber region between curves represents the temperature difference that drives heat transfer. Larger area = more efficient.
Cross-Section Cutaway — Shell & Tube vs Plate HX
Hot fluid
Cold fluid
Shell / frame / baffles / tube sheets
U-value badge highlights the currently selected exchanger type. PHX has 3–5× higher U than shell & tube due to turbulent flow in corrugated channels.
How Industrial Heat Exchanger Sizing Works
Sizing a heat exchanger for a manufacturing plant comes down to three numbers: heat duty Q (BTU/hr), LMTD (log mean temperature difference), and required surface area (ft²). Get these right and you pick the correct exchanger the first time.
1 Calculate Heat Duty (Q)
How many BTU/hr must be transferred? Calculated from hot-side flow, specific heat, and temperature drop. Everything else is sized around Q.
Solve the fundamental HX equation for area. Add 10–25% fouling allowance to get your design area for equipment selection.
Q = U × A × LMTD
A_clean = Q / (U × LMTD)
A_design = A_clean × (1 + fouling%)
Typical U (BTU/hr·ft²·°F):
Water-water S&T: 150–300
Steam-water S&T: 250–500
Water-water PHX: 500–1,000
4 Select the Unit
Match design area to a standard TEMA shell or plate frame. Shell & tube by shell diameter; plate HX by number of plates (~2–4 ft² each).
TEMA Shell ID Guide:
8" shell → ~20–50 ft²
12" shell → ~60–150 ft²
17" shell → ~150–350 ft²
21" shell → ~300–600 ft²
25"+ shell → 600+ ft²
Round UP to next standard size.
Add 10–15% additional margin.
Cross-Temperature Warning
In counter-current flow, the cold outlet can be hotter than the hot outlet — thermodynamically valid. However, if T_c,out ≥ T_h,in, LMTD is zero or negative and the exchanger cannot be sized. Always maintain at least 5–10°F approach temperature at each end.
U ≈ 120 BTU/hr·ft²·°F for oil-water S&T. Design area ~132 ft² → 17" TEMA shell, 16 ft tubes. Specify stainless tubes for cooling tower water.
🟠 Process Water Heater
Type: Shell & Tube (steam → water)
Hot: Steam 250°F → condensate
Cold: Process water 50°F → 180°F
Flow: 60 GPM cold side
Q: ~3,900,000 BTU/hr LMTD: ~105°F · Area: ~74 ft²
High U (~400) = small area despite large duty. 12" shell, 12 ft tubes. Install steam trap and condensate return on shell side.
🔴 Cooling Tower Loop
Type: Plate HX (water → water)
Hot: Process water 110°F → 85°F
Cold: Tower water 75°F → 95°F
Flow: 150 GPM hot side
Q: ~1,875,000 BTU/hr LMTD: ~12°F · Area: ~235 ft²
Low LMTD means large area despite high U. Plate HX ideal here — ~90–120 plates at 3 ft²/plate.
Typical U-Values — BTU/hr·ft²·°F
Fluid Service
Exchanger Type
U Min
U Max
Typical U Used
Water to Water
Shell & Tube
150
300
200
Steam to Water
Shell & Tube
250
500
350
Oil to Water
Shell & Tube
50
150
100
Water to Air/Gas
Shell & Tube
10
40
20
Water to Water
Plate (PHX)
500
1,000
700
Steam to Water
Plate (PHX)
600
1,200
800
Glycol 50% to Water
Plate (PHX)
400
800
550
Frequently Asked Questions
As fluids move through a heat exchanger the temperature gap between them changes continuously. A simple arithmetic average overestimates the driving force when ΔT₁ and ΔT₂ differ significantly. The logarithmic mean correctly weights the varying temperature difference along the length — always use LMTD, never the arithmetic average.
Plate HX is ideal when: (1) temperature approach is small (<10°F), (2) compact footprint is needed, (3) easy cleaning is required (food, pharma), or (4) pressure is below ~300 psig. Shell & tube is preferred for high pressure, steam condensing, gas/vapor service, or heavily fouling fluids like crude oil.
TEMA recommendations: treated cooling water 10–15%, cooling tower water 15–20%, river/well water 20–25%, crude oil 25–30%, steam (clean) 5–10%. Higher fouling factors add cost but prevent underperformance after months of service.
Clean area is the theoretical minimum assuming perfectly clean surfaces. Design area adds a fouling margin to ensure performance after months of service when scale or biofilm reduces the effective U-value. Always specify and purchase based on design area.