Heat Exchanger Sizing Calculator
Sizing Results ($A = Q / (U \Delta T_{lm})$)
What Is a Heat Exchanger Sizing Calculator?
A Heat Exchanger Sizing Calculator is a digital tool that computes the surface area needed to transfer a specific amount of heat between two fluids.
It uses the well-known equation:
[
A = \frac{Q}{U \times \Delta T_{lm}}
]
Where:
- A = Required Heat Transfer Area (ft²)
- Q = Heat Load (BTU/hr)
- U = Overall Heat Transfer Coefficient (BTU/hr-ft²-°F)
- ΔTlm = Log Mean Temperature Difference (°F)
This formula ensures your exchanger is large enough to meet heat duty requirements while avoiding unnecessary oversizing that increases cost and footprint.
How the Calculator Works
The calculator takes your key input parameters and computes the sizing automatically. Here’s what you’ll enter:
- Heat Load (Q) – The total heat to be transferred (in BTU/hr).
- Overall Heat Transfer Coefficient (U) – Selectable from common exchanger types (e.g., water-to-oil, steam-to-water).
- Temperature Inputs –
- Hot Fluid Inlet (°F)
- Hot Fluid Outlet (°F)
- Cold Fluid Inlet (°F)
- Cold Fluid Outlet (°F)
Once entered, the tool instantly calculates:
- ΔT₁ = Hot Inlet – Cold Outlet
- ΔT₂ = Hot Outlet – Cold Inlet
- ΔTlm using the Log Mean Temperature Difference formula for counter-flow configuration.
- A (ft²) = The required surface area for heat exchange.
The results appear neatly below the form, showing both the LMTD and the calculated area in an easy-to-read format.
Formula Behind the Scenes
The calculator uses the LMTD method, which is a standard in heat exchanger design.
If both temperature differences (ΔT₁ and ΔT₂) are close, the tool automatically adjusts to prevent calculation errors by approximating ΔTlm ≈ ΔT₁.
Example:
- Q = 100,000 BTU/hr
- U = 600 BTU/hr-ft²-°F
- Th,in = 180°F, Th,out = 160°F
- Tc,in = 80°F, Tc,out = 100°F
Then,
ΔT₁ = 180 – 100 = 80°F
ΔT₂ = 160 – 80 = 80°F
ΔTlm ≈ 80°F
A = 100,000 / (600 × 80) = 2.08 ft²
This means you need about 2.1 square feet of effective heat transfer surface for these operating conditions.
Why Accurate Sizing Matters
Incorrect heat exchanger sizing can cause:
- Insufficient cooling or heating
- Excessive pressure drop
- High operating costs
- Reduced efficiency and shorter equipment life
By using this calculator, you minimize guesswork and optimize your exchanger design from the very beginning — ensuring a balance between thermal performance, cost, and durability.
Supported Exchanger Types and U-Values
The calculator comes with pre-defined overall heat transfer coefficients (U) based on typical applications:
| Exchanger Type | Typical U Value (BTU/hr-ft²-°F) |
|---|---|
| Condensing Steam to Oil (Dirty) | 50 |
| Water to Oil (Shell & Tube) | 150 |
| Light Organics to Water | 350 |
| Water to Water (Shell & Tube) | 600 |
| Water to Water (Plate & Frame) | 800 |
| Condensing Steam to Water | 1200 |
Select the option that best matches your process for accurate results.
Key Features of This Heat Exchanger Sizing Tool
Instant Results: Calculates LMTD and surface area in seconds.
Error Validation: Warns if temperature inputs are unrealistic or physically impossible.
Modern Design: Dark-themed, mobile-responsive, and user-friendly.
Practical Defaults: Pre-filled values let you test calculations instantly.
Engineering-Grade Accuracy: Based on ASME and process design fundamentals.
Quick Steps to Use
- Enter your Heat Load (Q).
- Choose your Exchanger Type (U value).
- Input Inlet and Outlet Temperatures for both fluids.
- Click “Calculate Area”.
- View the LMTD and Required Area (ft²) instantly.
- If needed, click “Reset” to start fresh.
Important Notes
- The calculator assumes counter-flow configuration.
- Both temperature differences (ΔT₁ and ΔT₂) must be positive.
- It does not account for fouling factors, phase change, or heat losses.
- For detailed design verification, always consult manufacturer datasheets.
Why Use This Calculator?
This Heat Exchanger Sizing Calculator bridges the gap between theory and application. It helps you:
- Estimate equipment size quickly during the preliminary design phase.
- Verify existing exchanger performance.
- Compare design alternatives.
- Educate students or new engineers on the LMTD method in an interactive way.
It’s an ideal tool for chemical engineers, mechanical designers, and thermal system analysts who want practical insight — fast.
