The AAON BL Series Packaged Boiler Outdoor Mechanical Room is factory engineered to save time and money at the job site with pre-engineered pumping, piping and controls in one quick connect package. The BL Boiler is designed for indoor or outdoor application; the boiler can be installed in a traditional mechanical room, or occupied space inside the building can be maximized by moving the boiler package to the exterior of the building.