An HVAC boiler is a type of heating system that uses hot water or steam to heat a home or commercial building. Boilers are typically fueled by natural gas, propane, oil, or electricity. Boilers are used to heat water, which is then circulated through radiators, baseboard heaters, or radiant floor systems to provide heat to the building. Boilers can also be used to provide hot water for showers, laundry, and other uses. Boilers are an efficient and cost-effective way to heat a home or commercial building.