This is a high-performance, natural gas heater designed to quickly and efficiently heat pools and spas. It's known for its reliability, energy efficiency, and compliance with ASME standards. Here's a breakdown:  

• Pentair MasterTemp Series: This signifies a line of high-quality pool and spa heaters from Pentair, a trusted brand in the industry.  
• 400,000 BTU (British Thermal Units): This indicates the heating capacity of the unit. 400,000 BTUs is a high output, suitable for quickly heating large pools or spas, or for use in colder climates.  
• Natural Gas: This heater uses natural gas as its fuel source, which is a common and relatively cost-effective option.
• ASME (American Society of Mechanical Engineers) Certified: ASME certification means the heater meets stringent safety and quality standards for pressure vessels. This ensures safe and reliable operation.
• High Efficiency (HE): The "HE" designation indicates that this is a high-efficiency model. This means it's designed to maximize heat transfer and minimize energy waste, resulting in lower operating costs.
• Rapid Heating: The high BTU output allows for fast heating of pool or spa water.  
• Compact Design: Despite its high output, the MasterTemp is designed to be relatively compact, allowing for flexible installation options.  
• Durable Construction: Pentair heaters are built with durable materials to withstand the harsh outdoor environment and provide long-lasting performance.  
• Digital Controls: Many MasterTemp models feature digital controls for easy temperature setting and diagnostics.  

In summary: The Pentair MasterTemp ASME HEATER 400 Heater Natural Gas is a powerful, efficient, and reliable heater designed for quickly heating pools and spas. Its high BTU output, ASME certification, and high-efficiency design make it a top choice for pool owners who demand the best in performance and safety.