Hot Water Boilers

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Key Questions

The following key questions are answered in this module:

What is a boiler?
A boiler is a fuel-burning appliance that produces either hot water or steam that gets circulated through piping for heating or process uses.

What are the three main types of hot water boiler designs?
The three main types of hot water boiler designs are fire-tube, water-tube, and electric.

What are the three methods of heat transfer?
The three methods of heat transfer are radiation, convection, and conduction.

What are the classifications of boilers?
Boilers can be classifed as high pressure, low pressure, steam, and hot water.

What is convection?
Convection is the transfer of heat from a surface by means of a fluid.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

Hot water boiler types differ by their heat source and the relationship of the heat source to the water. The three main types are fire-tube, water-tube, and electric. Fire-tube hot water boilers rely on hot combustion gases passing through a series of metal tubes that are surrounded by water in a vessel. Heat transfers from the hot gases through the tube walls to the surrounding water. The hot gases often make two, three, or four passes through the water to increase the total amount of heat transfer and boiler efficiency. Fire-tube hot water boilers are relatively compact; the most common design for commercial heating applications has a horizontal shell and tube arrangement. In water-tube hot water boilers, the water flows through a series of tubes that are surrounded by hot combustion gases. Heat still transfers from the hot gases through the tube walls to the water, but in the reverse direction. Water-tube boilers tend to be more efficient than fire-tube boilers, because the higher density fluid (water) is inside the tubes. Also, because water-tube boilers contain less water than fire-tube boilers with the same capacity, they are inherently safer, have faster response times, and are available in larger capacities. Also, unlike fire-tube boilers, tubes can be added to some installed water-tube boilers to increase their capacity. Electric hot water boilers use electric resistance to generate hot water. Larger units used for hydronic heating of commercial buildings typically require three-phase power. Because they do not involve combustion, electric boilers are cleaner, quieter, have a smaller footprint, and are simpler to install than gas-fired or oil-fired boilers. However, they are usually more expensive to operate. An electric hot water boiler might be appropriate if emissions are an issue or a low cost supply of electricity is available.