In industry, fossil fuel-fired boilers are commonly used to produce steam or hot water for space and process heating. However, traditional boilers may not be flexible enough to respond quickly to demand surges during peak periods.
To compensate, processors and manufacturers often keep more than the required number of boilers running — usually at less than full capacity. When more steam or heat is required, the units are already in operation and so require less time to increase output. Even if burning at 75%, fossil fuel boilers take time to heat up internally.