Central Heating Boilers | Boilers

Many households in the United States are equipped with residential central heating boilers, which transmit heat to provide relief from cold winter conditions.  They are used for heating purposes in buildings since heat is required to operate water heaters and other heating systems.  The average residential boiler typically uses different controls to sequence the boiler.

There are differences in controls between steam and hot water boilers.  A Category I type is a residential boiler which is marked by non-positive, non-condensing vent pressure and incorporates natural draft appliances.

Thermostat Settings on Boilers

The typical temperature set point for most hot water boilers is 180 degrees Fahrenheit, while the low limit, or dead-band, is normally 40 degrees Fahrenheit and can be manually adjusted.  The aquastat of typical residential boilers maintains a manual set point inside the boiler’s heat exchanger by controlling the water temperature inside the boiler by sensing water temperature and cycling the burners.  A temperature sensing bulb is on the back of an aquastat and immersed in water.  On a call for heat, the thermostat turns on a circulator pump which starts the water circulating throughout the hot water loop.  Hot water (180 degrees) leaves the boiler on the supply side of the loop, and on the return side of the loop, cooler water returns to it.

When the temperature bulb on the aquastat senses the water temperature inside the boiler water jacket, it senses when water temperature falls below the low limit or dead-band setting then sends a signal to start the burners to heat the water to 180 degrees Fahrenheit, the high limit.  When the water temperature in the boiler water jacket falls below 140 degrees Fahrenheit, the aquastat turns on the burner to heat water returning from the loop.  When the water temperature inside the water jacket reaches 180 degrees, the burner shuts down at the aquastat’s signal.  The sequence resumes when the water temperature falls below the aquastat determined dead-band.


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