Hot Water Boilers

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Hot Water Boilers[edit]


They are also referred to as hydronic boilers. They are frequently applied in residential & commercial buildings for heating purposes. They are usually manufactured in small sized portable units for domestic applications whereas large sized units are put into use for industrial applications.

One can chose among variety of fuels such as propane, electricity etc. for hot water boilers operation but the most commonly used fuel source happens to be natural gas owing to its cost effectiveness. These boilers are extremely durable and offer long operational life. Besides, their usage involves less complication as compared to other heating systems. However, the installation procedure of hydronic boilers is quite expensive.

Just like steam boilers, hot water boilers also exist in two different configurations i.e. the fire tube boiler configuration and the water tube boiler configuration. The fire tube boilers are also referred to as shell type boilers owing to their construction.

Major components[edit]

Below mentioned are the key components used in the construction of hot water boilers:

  1. Thermostat which is mainly employed for controlling heat and temperature inside the system.
  2. A gas valve for regulating fuel gas flow
  3. A pressure gauge which is basically used to indicate the pressure of the water in the boiler.
  4. Water feed valve for adding water into the boiler system.
  5. Pressure reduction valve for lowering pressure inside the system.
  6. An air vent which allows the escape of redundant air from the system.
  7. An expansion tank which enables expansion of water upon heating.
  8. A flow control valve for controlling the flow of boiler water
  9. A pressure relief valve for pressure control
  10. A circulator which is usually a motorized electric pump used for circulation of water throughout the system.
  11. A drain valve


In a typical hot water boiler system, the fuel is introduced into a pressurized tank where combustion process takes place. A temperature controlling device called thermostat is included in the system which keeps a check on the fuel temperature. Within the pressurized tank, the water combined with a regulated quantity of air is supplied which initiates the fuel burning process. The products of combustion are then passed via pipe towards the cylinder which contains the water. Due to the heat supplied by the hot gases, the water inside the system gets heated. The resulting hot water is then finally distributed by means of an electric pump. The heated water is sent via another pipe to all the parts in the building requiring heat.
In hot water heating systems, the whole system is usually divided into different heating zones in a building. This zoning method offers following benefits:

  1. It results in efficient heating.
  2. It makes the living extremely comfortable.
  3. It makes the boiler operation very simple.
  4. It offers extremely cost-effective heating solution.

Radiant heating is one of the oldest techniques for generating hot water heating. It is usually applied owing to its highly efficient heating effect. With the advent of new technologies, radiant piping systems have been made extra robust as well as inexpensive. “Plastic tubing (which is a more economical choice than other piping materials) has made it conveniently possible for homeowners to have their floors, walls, driveways and pools heated hydronically.”[1] Distribution of heated water inside a hydronic boiler system can take place via following techniques:

  1. Radiators
  2. Baseboards
  3. Convectors and
  4. Vents, also referred to as hydro-air systems

Types of Hot Water Boiler Systems[edit]

There are four major types of hot water boiler systems available which are mentioned below:

  1. Closed System: In these types of systems, the water which gets evaporated and converted into steam is again put back into use by condensing the steam back to liquid form. This means that the 100 percent reutilization of the water takes place in closed systems.
  2. Open System: In these systems, the water is heated up but the evaporated water is not put back for reutilization inside the system.
  3. Single-pipe System: In these systems, two pipes are utilized. One pipe is used for carrying the heated water to the required location whereas the second pipe is used for returning the cool water back towards the boiler by means of a motorized pump.
  4. Gravity System: These are the older hot water boiling systems in which the water is carried back after heating via the gravity effect. Hence, in these systems, circulators are not required.

Main Features[edit]

Following are the significant features associated with the use of hot water boiler systems:

  • Although the installation of hot water boiler systems is extremely costly yet they are frequently employed for heating applications owing to their high efficiency and cost in comparison to forced-air boiler systems.
  • Since the hot water boiler systems are made up of aluminum fins and copper pipes, they tend to employ less metal for their construction and hence occupy comparatively smaller area.
  • Hydronic boilers typically offer small and uniform values of temperature as compared to forced-air boilers. Moreover, in these systems, the on-off switching action is usually prevented because of the ability of baseboard pipes to grasp the heat and liberate it over longer periods of time.
  • Another important feature regarding hot water boilers is that they dry the air inside the system to a very small extent only.
  • “A Hydronic boiler does not allot allergens, dust, combustions or mold by any products that enter living space. This is always an advantage, especially for a family that is sensitive with allergies.”[2]
  • The piping mechanism within a hot water boiler system is very exceptional and its correct implementation is very much responsible for the proper operation of the boiler.
  • A single hydronic boiler system per home is usually found adequate to produce necessary heating effect, unless it’s a big triple story house.
  • Hot water boilers are mainly employed for domestic heating applications, generally in the northern parts of Europe.
  • Hydronic boiler systems are mainly applied as central heating system inside buildings to give heating effect to the areas, which are otherwise very cold.
  • “A typical hot water boiler operates throughout the winter with a water temperature determined by the Aquastat, or low limit, setting (an Aquastat is like a thermostat that senses the water temperature inside the boiler and shuts off the burner when the water is hot enough).”[3]


It is very important to carry out periodic maintenance of a typical hot water boiler system; otherwise the boiler may burst out resulting in fires or explosions. The cylinder used inside the boiler system must be regularly drained and cleaned to avoid clogging of pipes because of surplus mineral deposits. This mineral build up takes place due to the nitrate components present in the water.

Oiling of pipes must be regularly done in order to provide lubrication to them. Also, the pipes must be carefully inspected at regular intervals for detecting leakage points. Moreover, the pressure gauge incorporated within the system needs to be cautiously checked for any type of irregularity in the pressure. To ensure proper boiler operation, one must get the boiler inspected and certified by a qualified boiler professional.

See Also[edit]



Steam Boilers



Oilheat America
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