What describes a sectional boiler?

A sectional boiler is characterized by being constructed from vertical sections or units, which allows for ease of transportation, installation, and maintenance. This modular design enables the boiler to be assembled on site, typically in locations with limited access, and allows for the option to expand the capacity by adding more sections if needed. This feature makes sectional boilers versatile and adaptable to various heating requirements.

The other choices do not accurately describe the nature of sectional boilers. While they can be composed of several sections, they are not necessarily made up of large, single units, nor are they fixed in size without the option for adjustment or modification. Additionally, a significant foundation may not be required for assembly, as the modular design allows for installation in various types of settings, making sectional boilers more flexible in terms of placement.