air filters - A hot water boiler is an enclosed container that allows heat to be transmitted into water till the time it becomes heated water. The hot water is then effectively utilized for transferring the heat to where it is needed. A hot water boiler is filled with water, unlike the steam boiler.
However, like the steam boiler, hot water boilers have many add-ons to function effectively. The presence of aquastat serves a two-fold objective. It monitors the temperature in which the boiler runs, and offers a low-voltage transformer and relay to control the circulator.