Boiler heating systems are another form of an HVAC system designed to heat a building. Instead of forcing warm air through duct work – which is what a furnace does – boilers use water to distribute heat through a series of pipes and pumps. If you’ve seen a radiator in a house, school or office building, that was probably a boiler system (unless it was a space heater type of device). Radiators give off heat thanks to the hot water that’s inside of them. Cooler water is returned to the boiler to be reheated. Boilers can run on gas or heating oil as a fuel source to heat the water. Boiler equipment includes thermostats, aquastats, valves, radiators and more.