Modular boilers are small in size and capacity and are usually used to replace several small boilers instead of one large boiler. These modular boilers pass through standard ports and are portable through stairs and elevators. These devices can be arranged in different order to make the most of small places or embed other equipment in those places. These boilers can efficiently provide the required heating load.

Leaks may occur in the hot water distribution system. This leakage increases the water and energy consumption of the system as well as the damage caused by the water leakage. Compensation water must be provided for the hot water and steam distribution system to replace the steam and water lost through the leak. This is an easy solution to ensure there is permanent water in the system. It is best to install a measuring device on the system compensation line. The measuring device should be checked weekly for unexpected system water loss.

Parallel controls use separate motors to regulate fuel flow and airflow, enabling each motor to be tuned throughout the boiler ignition range. During installation, to points are usually drawn to create a curve of airflow corresponding to the fuel flow. The air-fuel ratio can be varied along the ignition range to prepare the optimal ratio in different ignition conditions. Also with the use of electronic dampers, this method of control is very reproducible.

Figure shows the combustion efficiency chart for natural gas fuel with electricity, which shows the relationship between excess air and flue gas temperature with combustion efficiency. For example, by following the Step line in the diagram, the amount of oxygen at % in the flue gas (as shown in the diagram equals approximately % of the excess air) and ° F as the flue gas temperature rises, the corresponding combustion efficiency is about . % is observed. At the same increase in the flue gas temperature by degrees Fahrenheit, the Step line shows that reducing the oxygen in the flue gas to % increases the combustion efficiency to about .%. The lower the percentage of oxygen in the flue gas, the less heat is transferred to the excess oxygen, resulting in increased fuel efficiency. The higher the efficiency, the more heat will be transferred to the inlet water instead of to the flue gas, thus reducing the flue gas temperature.

Steel boilers, as their name implies, are made of steel and are usually made of horizontal cylinders. Steel boilers have a combustion chamber in which pipes are placed around this chamber. The pipes that are installed around the combustion chamber of steel boilers are made of a special alloy so that they do not burn or damage in the face of a direct flame. These pipes are called (fire pipes). Steel boilers are divided into friends from the point of view of heat transfer, which are as follows.