Pentair Sta-Rite Max-E-Thermostat 400K BTU Heater SR400NA

The Pentair Sta-Rite Max-E-Therm SR400NA Natural Gas Pool & Spa Heater delivers powerful 400,000 BTU heating performance in a compact, energy-efficient design. Built for fast heat-up times and reliable operation, Max-E-Therm heaters are trusted for both residential and light commercial pool and spa installations.

Featuring a high-efficiency copper heat exchanger , advanced digital controls, and a corrosion-resistant composite cabinet, the SR400NA provides consistent temperature control while operating quietly and efficiently. Its space-saving footprint and straightforward installation make it an excellent choice for equipment pads with limited room—without sacrificing heating power.

Frequently asked questions

How do I size a pool heater?

Heater sizing follows pool surface area, the temperature rise you want and how exposed the pool is to wind. A larger BTU rating heats faster and cycles less; an undersized heater runs continuously and still struggles on cold nights. Gas heaters also need a gas line and meter capacity that can supply their rated input.

What is the part number for this heater component?

Sta-Rite lists this heater component under part number SR400NA. Quote SR400NA when you cross-reference against your equipment manual, an existing part, or a parts diagram, so you are comparing the same revision.

What routine maintenance does a pool heater need?

Keep water chemistry balanced, because low pH and high calcium hardness are the two most common causes of premature heat exchanger failure. Beyond that: keep the cabinet clear of debris, check for rodent nests before each season, and have the burner and gas train inspected periodically.