Boiler furnaces and HVAC systems are both used to heat and cool buildings, but they differ in how they do so. Boiler furnaces use hot water or steam to heat a building, while HVAC systems use air. Boiler furnaces are typically used in larger buildings, such as commercial buildings, while HVAC systems are more commonly used in residential buildings. Boiler furnaces are more efficient than HVAC systems, but they require more maintenance and are more expensive to install. HVAC systems are more cost-effective and require less maintenance, but they are not as efficient as boiler furnaces.