Hot Water Boilers

Hot water boilers are the most common heating system that are used in homes and large industries. This particular boiler functions by applying heat to water. Most of these units use electricity to run – but a few can also run on natural gas and propane. They come in portable and large units and are some of the most expensive to install because of the numerous pipes running to and from them. However, these last longer than most units and do not break down as easily.


  • Thermostat that is used to regulate the heat settings.
  • The gas valve.
  • Pressure gauge that monitors the water pressure.
  • Water feed valve.
  • Pressure reducing valve
  • Air vent that draws out unwanted air.
  • Expansion tank that allows water to expand when it is being heated.
  • Flow control valve that will regulate the flow of the water.
  • Pressure relief valve
  • Circulator
  • Drain valve


There are two common types of hot water boilers; the water tube and fire tube. The fire tube – also called the shell type uses hot gases that will run through the inside of the tube in order to heat the water. The water tube works by applying the heat around the outside of the water container so that the water will heat up from inside.


  • There are four different types of systems that the unit might use. The closed system will reuse all of the water that has evaporated after it has finished heating. This evaporated water will cool down and be reheated.
  • The open system is similar to the closed and will heat the water – but will not reuse any of it.
  • The single pipe system uses two pipes. One of the pipes will take the hot water to where it needs to be heated and the other will bring back the water that is cold by using an electric pump.
  • The gravity system will transfer the water after it has been heated by using natural gravity. No circulators are used in older boilers with this system.

How It Works

When the boiler is turned on the thermostat (which you might need to adjust) will regulate the temperature of the water. The water will be combined with a certain amount of air that is contained within a pressurized tank. The electricity will than transfer the water to the cylinder where it will be warmed. The hot water is transferred through a circulator to a separate pipe to give the sink or other area the hot water that it needs.