There are many different types of boilers in the boiler room today in a variety of heating applications. There are two main categories of boilers among the different types of boilers and those two categories are steam and hot water boilers. Either of those categories can be fueled by oil, gas, or electric (although electric is uncommon for steam boilers). They have different designs and piping configurations as a steam boiler system is designed to turned the water into steam and uses gravity and pressure to deliver the heat and the hot water boiler systems are designed to simply make hot water to be circulated (by a circulator or pump) through a piping system to provide heat. Typically, hot water boilers are more efficient than steam boilers for a few reasons. First, there is less heat loss throughout the hot water piping and the shell of the boiler because the hot water boiler operates at a lower temperature than the steam boiler. This means there is less heat loss throughout the entire boiler and piping system. Secondly, because the hot water boiler operates at a lower temperature, it requires less fuel or energy to convert into heat. What kind of boiler do you have in your boiler room?

Water Tube Boilers

Water tube boilers have many different tubes inside of it that have water circulating through them. Hot combustion gases surround these tubes and an exchange of heat is realized from the combustion gases to the tubes and water. The water tube boilers can be built for higher capacities and pressures than the fire tube boilers because the steam and/or hot water is confined in the tubes.

Water Tube Boiler sizes range from from 10 million BTU/h boilers all way up to 300 million BTU/h and these boilers are generally found in medium to large commercial/industrial use and can be either steam or hot water boiler in low to high pressure boiler applications. These boilers can be either oil boiler, coal boiler, or gas fired boiler and pass hot flue gases around tubes filled with water. Boiler combustion efficiencies depend on several factors for these boilers including: whether it is steam boiler or hot water boiler, combustion controls, flue dampers, frequency of tune-ups and/or air and/or water pre-heaters (boiler economizers).

Fire Tube Boilers

Fire tube boilers confine the combustion process and gases in tubes and water circulates around these tubes. Some fire tube boilers have turbulators inside of the tubes to cause turbulence of the flue gases. This increases the heat absorption into the water which makes the boiler more efficient.

Fire Tube Boilers range in sizes from .6 million BTU/h up to 50 million BTU/h boiler these use hot flue gases passing through tubes submerged in water generally found in medium to large boiler commercial/industrial use and can be either steam or hot water boilers in low to medium pressure applications. Again as with the water tube boiler combustion efficiencies depend on several factors as noted above. There are various names applied to different fire tube boilers such as: Scotch Marine, locomotive, firebox, and vertical or horizontal return tube.

Condensing Boilers

Between steam and hot water and water tube and fire tube boilers there exists conventional atmospheric boilers and condensing boilers. The condensing boiler is far more efficient than the conventional atmospheric boiler. A condensing boiler typically has two heat exchangers and absorbs more heat from the flue gases. It actually absorbs so much heat from the gases that moisture in the flue gases condenses and needs a drain to drain off. This condensed liquid is highly corrosive and it is necessary for the manufacturer to build the condensing boiler out of special materials to prevent corrosion to the equipment. Typically, the flue is PVC pipe or stainless steel and is resistant to the corrosive effects of the condensation. Additionally, because so much heat is removed from the flue gases, the products of the combustion process need help to be safely vented. Usually a fan is used to either push or pull these gases out of a vent. Condensing boilers are typically rated at 90 plus efficiency ratings whereas the conventional atmospheric boilers are typically rated at around 80 percent plus.Conventional Atmospheric Boilers Conventional atmospheric boilers do not use a blower motor to remove the combustion byproduct gases. Instead they rely on the combustion gases to have enough heat to cause the gases to rise through the flue and channeled safely outside of the dwelling. If for some reason too much heat is removed from the flue gases condensation can occur inside the flue or chimney. This condensation can have corrosive effects to both the flue and the chimney and cause severe problems. It is important that a qualified HVAC technician inspect the boiler and that they check of the temperature of the flue gases. Using a combustion analyzer, a qualified technician can tune the boiler to make sure that the temperature of the flue gases is set to optimum levels so that the gases will properly vent and that the gases do not have too much heat in them. If the flue gases are too hot then you are losing efficiency up the flue. If the flue gases do not have enough heat in them then you can have condensation issues which cause corrosion. Have your boiler checked and inspected at least annually to maintain optimum efficiency.Electric Boiler One other type not mentioned above is the electric boiler. One could say that an electric hot water heater is an electric boiler although there are electric boilers that can heat water to steam temperatures. Boilers can use many types of fuels (oil, gas, coal, wood, and electric power) to heat water (or other liquids) but the main focus of Boiler Types article was to categorize the mechanical aspects and differences.