Fire Tube Boilers
The term "fire tube boiler" is used to refer to a boiler with a specific type of heat exchanger where the combustion gases travel through tubes that are surrounded by water. Fire tube boilers always utilize induced draft systems. An induced draft system utilizes a fan that either pushes or pulls the combustion air threw the tubes. Nearly every fire tube boiler utilizes a large primary combustion chamber that contains the fuel and air while combustion is taking place. After the fuel is burned, the hot gasses reach the back of the boiler and then reverse direction by entering the fire tubes. As the hot gasses travel towards the front of the boiler the heat of the hot gasses is transferred to the tubes, and then in turn transferred to the water surrounding the tubes. Some fire tube boilers utilize only one "pass", while others utilize multiple "passes".
Fire tube boilers can have a wide range of efficiencies. Some fire tube boilers reach efficiencies up to 96%, while others are in the range of 70%. Fire tube boiler manufacturers consider several variables when designing the boilers. While combustion air condensation is indicative of high efficiency, if the boiler is not designed to properly handle the condensation, the boiler's components may be damaged. In some circumstances, boiler manufactures need to alter the design of the boiler to reduce the efficiency of the boiler to avoid problems caused by condensation. Fire tube boilers that are designed to obtain high levels of efficiency, like the Triangle Tube Prestige Boiler, utilize stainless steel heat exchangers to deal with the corrosive attributes of the acidic condensation produced during the heat transfer process, and are also designed to properly drain the condensed water.
The design of fire tube boilers offers some benefits and disadvantages compared to other types of boiler designs. Although large fire tube boilers often have provision for cleaning and maintenance of the fire tubes, small fire tube boilers often do not. If the combustion of the boiler is too rich, carbon may form in the fire tubes, which often perpetuates the formation of carbon by further reducing the amount of O2 entering the combustion chamber. A rich burn is a burn that has too much fuel and too little oxygen. If the carbon is not removed from the fire tubes the tubes may become plugged with carbon, and the boiler will cease to function. The cleaning or brushing of fire tubes in large fire tube boilers is very important not only because it keeps the boiler operating, but also because it maintains good efficiency. Carbon is an insulator, and very small amounts of carbon on the inside of a heat exchanger have a considerable effect on the efficiency of any system.
One benefit of fire tube boilers is than they are often able to deliver constant and controlled supply water temperatures due to the fact that the capacity of water in a fire tube boiler tends to be much higher than that of a water tube boiler. With water tube boilers the water in the boiler resides in the pipes, while with a fire tube boiler, the pipes hold only the combustion gases while the water is housed all around the fire tubes. Because every modern, high efficiency boiler either utilizes a fire tube heat exchanger or a water tube heat exchanger, something like a high efficiency tank less water heater must be either / or. When utilizing a modulating burner to control the discharge water temperature, the system needs to react less quickly in a fire tube boiler when the supply water temperature exceeds or falls short of the supply water temperature set point.
Fire tube boilers tend to have excellent water flow characteristics Because the water basically enters a large tank and then leaves a large tank, the water is able to flow relatively freely threw the heat exchanger. The water flow characteristics of a boiler are important for several reasons. Firstly, when installing a boiler with poor water flow characteristics, the total job cost may go up if oversized pumps need to be used to overcome the water flow issue. Also notable is the fact that in situations like the utilization of a boiler with poor water flow characteristics as a water heater (for domestic hot water), the pressure of the system will tent to drop when more hot water is used.
The repair of a fire tube boiler tends to be more difficult than that of a water tube boiler. Because a fire tube boiler passes hot combustion gasses threw the tubes, it is necessary to use steel or stainless steel tubes. While some water tube boilers may also use steel or stainless steel heat exchangers, often copper tubes are used. Copper may be brazed with very little difficulty, however, the replacement of steel tubes often requires a complicated "rolling" processes in which the entire tube is replaced and the ends of the tube are rolled backwards to create a compression seal against the boiler's header. While steel and stainless steel tubes will rust and fail, generally speaking, copper tubes seem to be more resilient to corrosion. In smaller fire tube boilers, if a one of the fire tubes fail, usually the boiler needs to be replaced, while with water tube heat exchangers, many times the tubes can be repaired in a cost effective mannor.
If you live in the State of Michigan and need boiler repair, boiler installation, boiler service, or just a good boiler repair company, give us a call. We have two decades of experience working on boilers and hydronic heating systems, our rates are competitive, and we always treat our customers the way that we would like our families to be treated if they were in your shoes. If you would like to learn more about some of the work that we have done, and look into some of our references that are local to you, just navigate to our contact page and click on the link to your township or city. We have listed a few references from several areas in Macomb and Oakland Counties that are organized under their respective township/city and area codes.
Boiler Service and Maintenance
- CSD-1 Reports