Which type of boiler is least commonly used for low pressure heating service?

In low-pressure heating applications, water tube boilers are generally less prevalent compared to other types. Water tube boilers are designed to handle high-pressure systems and are therefore commonly used in industrial applications where higher pressures are necessary for increased heat transfer efficiency. Their construction allows for a large surface area for heat exchange, but this complexity and capacity make them less suitable for the straightforward and less demanding requirements of low-pressure heating.

In contrast, cast iron boilers are often utilized in residential heating systems due to their durability and ease of maintenance at low pressure. Fire tube boilers, while capable of handling both low and high pressures, are frequently used for heating purposes in commercial settings because they can efficiently generate steam or hot water. Electrical boilers can also be used in low-pressure scenarios, particularly where there is limited access to gas or where there are regulatory restrictions.

Thus, while water tube boilers excel in high-demand environments, their design and operational characteristics align less with low-pressure heating needs, making them the least commonly used choice in this context.