Pentair Max-E-Therm® 400 Natural Gas Pool & Spa Heater 400K BTU
The Pentair Max-E-Therm® 400 Natural Gas Pool & Spa Heater 400K BTU lets you save money and energy without compromise. Already known for dependability and efficiency, the Max-E-Therm now offers smart features and an optional energy-saving automatic bypass to help ensure your pool is ready whenever you are.
Built by Pentair (Sta-Rite) with an 84% efficiency rating — rated first in its class for highest energy efficiency — the Max-E-Therm 400 features a lightweight, compact Dura-Glas® rustproof matte black enclosure, Low NOx certification, and direct compatibility with Sta-Rite System:3 Mod Media filters. CSA certified for indoor and outdoor use. Backed by a 2-year warranty.
⚠️ Professional Installation Required. Pool heater installation involves gas line connections and electrical wiring. Always use a licensed contractor to ensure safety, code compliance, and warranty validity.
Key Features
400,000 BTU — 84% Efficiency
Rated first in its class for highest energy efficiency at 84% — the best-in-class efficiency rating.
Lightest Heater in Its Class
138 lb — the lightest 400K BTU pool heater available, making installation easier.
Compact Design for Retro-Fit
Ideal for retrofit installations where space is limited on an existing equipment pad.
Optional Automatic Bypass
Energy-saving automatic bypass option helps optimize operating costs.
Easy Gas Source Switching
Convert between natural gas and propane with installation of a separate orifice.
Dura-Glas® Rustproof Housing
Sleek matte black enclosure resists rust and corrosion for long service life.
Low NOx — Environmentally Friendly
All units are Low NOx certified.
Sta-Rite System:3 Compatible
Direct-connects to Sta-Rite System:3 Mod Media filter or fits other systems easily.
Indoor and Outdoor Certified
CSA certified for both indoor and outdoor pool and spa installations.
2-Year Warranty
Pentair residential warranty coverage.
Who It's For
- Pool and spa owners who want the highest efficiency 400K BTU natural gas heater available
- Retrofit installations where a compact, lightweight heater is essential
- Sta-Rite System:3 filter owners who want direct heater integration
- Anyone who may want the flexibility to switch between natural gas and propane in the future
Specifications
Heating Performance
| BTU Input | 400,000 BTU |
| Thermal Efficiency | 84% |
| Fuel Type | Natural Gas (convertible to LP) |
| Emissions | Low NOx |
| Flow Rate | 40–120 GPM |
Construction
| Enclosure | Dura-Glas® (Rustproof, Matte Black) |
| Control Type | Digital |
Installation
| Voltage | 120V / 240V |
| Frequency | 60 Hz |
| Phase | Single |
| Application | Indoor / Outdoor / Pool / Spa |
Physical
| Product Weight | 138 lb |
| Cabinet Dimensions | 25.15 W × 30 D × 26 H in |
| Shipping Dimensions | 27.75 × 34.25 × 32 in |
Approvals & Warranty
| Certifications | CSA Certified |
| Energy Efficient | Yes (Green Certified) |
| Warranty | 2 Years |
What's in the Box
- Pentair Max-E-Therm 400 Natural Gas Pool & Spa Heater
- Union Fittings
- User Manual
Warranty
The Max-E-Therm 400 comes with a 2-year manufacturer warranty from Pentair. Clearflow Pool Supply is an authorized Pentair dealer and will assist with any warranty service needed.
Downloads
Frequently Asked Questions
How does the Max-E-Therm 400 compare to the MasterTemp 400K?
Both are 400K BTU Pentair natural gas heaters but they're different platforms. The Max-E-Therm features the Dura-Glas rustproof enclosure, 84% efficiency (vs. MasterTemp's standard rating), and is designed with a different cabinet footprint that makes it especially well-suited for retrofit and compact installations. The Max-E-Therm also directly integrates with Sta-Rite System:3 filters.
Can I convert this to liquid propane?
Yes. The Max-E-Therm can be converted from natural gas to liquid propane by installing a separate LP orifice kit (sold separately). This makes it a flexible option if your fuel source ever changes.
Does this heater require professional installation?
Yes. Gas heater installation involves connecting to a natural gas supply line, electrical wiring, and proper venting. A licensed pool contractor or plumber must perform the installation to ensure safety, local code compliance, and warranty validity.
What is the automatic bypass option?
The optional automatic bypass diverts flow around the heater when it's not actively heating, reducing resistance in the system and lowering pump energy consumption. It's an add-on for installations where maximum energy efficiency is a priority.
What size pool is the 400K BTU suitable for?
As a general guideline, 400,000 BTU is typically suited for pools in the 30,000–50,000 gallon range depending on climate, desired temperature rise, and heat loss factors. A licensed pool professional can calculate the correct BTU requirement for your specific pool and location.