Manufacturers Best Practice Guide

Steam: Boiler Basics

Most often, steam is generated onsite by a boiler system, which can also provide space heating and hot water for the building. Five major steam-intensive industries are host to most of the nation's industrial boilers. Food, paper, chemicals, refining and primary metals have 71% of the boiler units and 82% of the boiler capacity in the U.S.

Boilers come in a wide variety of sizes, fuel sources and designs. Once on site, each boiler system is uniquely configured to meet operational requirements and space capacity. Despite this variability in form, all boilers share a common function: to produce steam or hot water (thermal energy) by combusting fuel in an enclosed and pressurized tank. A "rule of thumb" is that boiler efficiency increases 1% for every 15% reduction in excess air or 40ºF reduction in stack gas temperatures.

Industrial Boilers


Industrial boilers can be configured to combust either fossil fuels or biomass fuels. Natural gas is the predominant fuel source, powering 78% of all industrial boilers and 56% of total U.S. industrial boiler capacity. Petroleum-based oil and coal are less common fossil fuel options. Biomass fuels are most common in facilities that have combustible by-products, such as wood and wood waste, industrial waste, fast-growing plant and tree materials, aquatic plants and algae, animal waste, organic municipal or agricultural crops and their residue. Choosing between boiler designs will often depend on which fuel source is most affordable and can be supplied reliably.

A boiler is a major expense for any manufacturer. Typically, an industrial boiler system is installed for the life of the facility, even if plant operations or ownership change over time. Once in operation, utility costs quickly add up.

To improve boiler efficiency and reduce operating costs, consider both proper maintenance and tuning, which extends the usable life of the system, and strategic equipment upgrades. In most cases, unless the boiler is very old, replacing a boiler is not a cost-effective option as boilers often last the life of the building. But if retiring an old boiler is an option, consider the many benefits of a combined heat and power (CHP) system.

If it is a high-pressure steam boiler, adding a steam-powered extraction or backpressure turbine enables the boiler system to generate electricity, a process known as cogeneration or CHP. Conversely, waste heat from onsite electricity generation via gas turbine or reciprocating engine can be captured and reused to heat or cool air or water, minimizing or eliminating entirely the need for boiler operations.

Boiler efficiency is expressed by the amount of fuel needed as an input - not by the amount of steam produced or system pressure. However, the easiest way to measure efficiency is to look at the amount of waste heat, that is: Boiler efficiency = 100% - heat losses.

Thus, a boiler that is 75% efficient converts three-quarters of the input fuel into steam, but losses 25% of the fuel as waste heat.

Factors affecting boiler efficiency include the air-to-fuel ratio and combustion efficiency. Boiler efficiency can also be improved significantly by reusing waste heat exiting the stack.