Boilers transmit heat from water. They are often used to heat 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 steam and hot water boilers. A Category I boiler is a residential unit which is marked by non-positive, non-condensing vent pressure and incorporates natural draft appliances.
How Does it Work?
Typically, the set point is 180 degrees. The lower limit, or dead-band, is normally 40 degrees Fahrenheit. The aquastat controls water temperature inside the boiler by sensing water temperature and cycling the burners accordingly. A temperature sensing bulb is immersed in the water and if heat is needed, the thermostat turns on a circulator pump to begin circulating the water throughout the hot water loop. Hot water (180 degrees) leaves the boiler on the supply side of the loop and cold water comes back.
When the temperature bulb senses water temperature falling below the dead-band setting, it sends a signal to start the burners to heat the water to 180 degrees Fahrenheit. 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, it then turns off when the water has again reached 180 degrees. The sequence resumes when the water temperature falls below the dead-band.