Boilers are made all over the world. The guidelines they are built by differ.  Manufacturers have choices to follow industry practices and safety guidelines that have been proven, or they choose not to.  The quality boiler will be ASME backed, have a UL approval, and be made to standards exceeding the minimum required. Reimers makes boilers for steam and hot water. They are heavy steel construction, and available in many KW inputs. Tanks and other accessories are ready to ship too. Voltages up to 600 can be ordered. Blowdown tanks of vented and closed design allow for easy maintenance.