Cornish boiler — typical overall length range Select the most typical range for the length of a Cornish boiler used in industry.

Introduction / Context:
Identifying realistic dimensional ranges helps distinguish classic shell boilers during design problems and site identification. The Cornish boiler, with a single internal furnace tube, has characteristic proportions different from the two-flue Lancashire boiler.

Given Data / Assumptions:

• Traditional Cornish construction (single furnace flue inside a horizontal cylindrical shell).
• Industrial service at relatively modest pressures.

Concept / Approach:
Handbook values place Cornish boiler lengths roughly in the mid-single-digit metres up to about 7 or 8 m for common sizes, while Lancashire shells are often longer. Among the choices, 5 to 7.5 m matches conventional practice most closely.

Step-by-Step Solution:

Verification / Alternative check:
Old design tables and museum specifications show Cornish boilers commonly around 5–7 m long for moderate duties.

Why Other Options Are Wrong:

• 2–4.5 m or 3–5 m: undersized for standard installations.
• 7–9 m: more typical of larger Lancashire units.
• 9–12 m: uncommon for the classic Cornish form.

Common Pitfalls:
Confusing Cornish with Lancashire proportions; forgetting space for reversal chambers and brick settings.

Final Answer: