---
title: "Fire tube versus water tube boilers"
subject: "Applied Thermodynamics"
chapter: 1
key: "semester_3/applied_thermodynamics:fire-tube-water-tube-difference"
source: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/fire-tube-water-tube-difference
site: BCT Engineering
---

# Fire tube versus water tube boilers

Applied Thermodynamics · Chapter 1: Boilers

- Asked in: year not given, 6 marks
- Video: [Comparison Between Fire Tube And Water Tube Boiler](https://www.youtube.com/watch?v=0fley-DLWyc) — BEST MECHANICAL ENGINEERING
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/fire-tube-water-tube-difference
- Whole chapter: https://www.bctengineer.com/md/semester_3/applied_thermodynamics/chapter-1

## Question

Differentiate between fire tube boilers and water tube boilers, giving two examples of each.

## Short answer

In fire-tube boilers, hot gases flow through tubes surrounded by water; they produce low-to-medium pressure steam slowly, e.g., Lancashire, Cochran. In water-tube boilers, water flows inside tubes with hot gases outside; they deliver high-pressure steam quickly and are more compact, e.g., Babcock and Wilcox, Stirling.

## Answer

In a **fire tube boiler** the hot flue gases pass through tubes surrounded by water. In a **water tube boiler** water flows inside the tubes and the hot gases pass outside them.

| Point | Fire tube boiler | Water tube boiler |
|---|---|---|
| Hot gases | Inside the tubes | Outside the tubes |
| Water | Outside the tubes, in the shell | Inside the tubes |
| Steam pressure | Low to medium, up to about 25 bar | High, up to 100 bar and above |
| Steam capacity | Limited, up to about 10 t/h | Large, up to several hundred t/h |
| Steam raising | Slow, large water content | Quick, small water content |
| Explosion risk | Serious, large water volume | Less serious, small drum and tubes |
| Floor space for same output | More | Less |
| Cost and transport | Cheaper, simple, easy to install | Costlier, erected at site |
| Water quality | Tolerates poor feed water | Needs well-treated water |
| Response to load change | Poor | Good |
| Cleaning and inspection | Easy internally | Tubes are cleaned individually, harder |

**Examples:** Fire tube: Lancashire, Cornish, Cochran, locomotive boiler. Water tube: Babcock and Wilcox, Stirling, Yarrow.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In which way do fire tube and water tube boilers differ in the position of gases and water?
   A. Fire tube: water inside tubes, gases outside; water tube: gases inside tubes
   B. Fire tube: gases inside tubes, water outside; water tube: water inside tubes, gases outside
   C. Both have hot gases inside the tubes
   D. Both have water inside the tubes
   Answer: B. In fire tube boilers hot gases pass through tubes surrounded by water; in water tube boilers water is inside the tubes. (Key point: Basic difference)

2. Which boiler type is suited to high pressure (up to 100 bar and above) and large capacity?
   A. Fire tube boiler
   B. Both equally
   C. Water tube boiler
   D. Neither; both are limited to about 25 bar
   Answer: C. Water tube boilers handle high pressure and large capacity; fire tube boilers are limited to about 25 bar and 10 t/h. (Key point: Pressure and capacity)

3. Why is the explosion risk of a fire tube boiler more serious than that of a water tube boiler?
   A. It operates at much higher pressure
   B. Its tubes are very thin
   C. It has a small water content
   D. It holds a large volume of water in the shell
   Answer: D. The large water volume in a fire tube shell releases much energy on failure, whereas a water tube boiler has a small drum and tubes. (Key point: Explosion risk)

4. Which boiler can tolerate poorer feed water?
   A. Fire tube boiler
   B. Water tube boiler
   C. Neither tolerates any impurities
   D. Both need identical treatment
   Answer: A. Fire tube boilers tolerate poor feed water; water tube boilers need well-treated water. (Key point: Feed water quality)

## Related in Applied Thermodynamics

- [Babcock and Wilcox water tube boiler](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_thermodynamics%3Ababcock-wilcox-boiler-working) — Applied Thermodynamics, chapter 1

## Related in other subjects

- [Airplane dropping water on fire](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_mechanics_dynamics%3Aairplane-water-drop-distance) — Applied Mechanics (Dynamics), chapter 1
- [Two-element array: broadside and end fire](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Atwo-element-array-broadside-endfire) — Propagation and Antenna, chapter 2
- [Two-element array and end fire pattern](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Atwo-isotropic-endfire-pattern) — Propagation and Antenna, chapter 2
- [Differential U-tube manometer between two pipes](https://www.bctengineer.com/question.md?key=semester_4%2Ffluid_mechanics_mechanical%3Adifferential-manometer-pipes) — Fluid Mechanics, chapter 2