Calculation Mode:

Size from Process Duty Fuel Calc (Known Duty)

Calculate heat duty from process fluid conditions, then size radiant and convection sections.

Process Fluid

Fluid Type

Flow Rate

Inlet Temperature

°F

Outlet Temperature

°F

Operating Pressure

psig

Fluid Specific Gravity

air/water=1

Specific Heat (Cp)

BTU/lb-°F

Leave 0 for auto-estimate based on fluid type

Known Heat Duty

Absorbed Duty

MMBTU/hr

Process Outlet Temperature

°F

Used for tube wall temperature estimate

Heater Design

Heater Type

Tube OD

inches

Tube Wall Thickness

inches

Sch 40: 0.337" for 4.5" OD

Tube Material

Design Factor

Typical: 1.10–1.25 over process duty

Fuel & Combustion

Fuel Heating Value (HHV)

BTU/SCF

Fuel Heating Value (LHV)

BTU/SCF

Excess Air

Typical: 15-25% for natural draft, 10-15% for forced draft

Ambient Temperature

°F

Learn the Theory

Radiant heat transfer, convection design, tube metallurgy, API 560 standards, and efficiency optimization

Read Engineering Guide

Engineering Basis

Process Duty

Q = ṁ × Cp × (T_out − T_in)

Tube Wall Temperature (API 530)

T_wall = T_fluid + q × (1/h_i + t/k)

API 560 API 530 GPSA Ch. 8

Fired Heater Quick Reference

Radiant fraction65–75%

Max flux (gas)10,000 BTU/hr-ft²

Gross efficiency80–92%

Excess air15–25%

Stack temp350–500°F

Fired Heater Sizing Calculator

Process Fluid

Known Heat Duty

Heater Design

Fuel & Combustion

Learn the Theory

Engineering Basis

Results

Fired Heater Quick Reference

Fired Heater Sizing Calculator

Process Fluid

Known Heat Duty

Heater Design

Fuel & Combustion

Learn the Theory

Engineering Basis

Results

Fired Heater Quick Reference

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