Pentair Max-E-Therm® 400 HD Natural Gas Pool & Spa Heater 400K BTU
The Pentair Max-E-Therm® 400 HD Natural Gas Pool & Spa Heater 400K BTU adds heavy-duty cupro nickel tubing to the proven Max-E-Therm 400 platform — built for the most demanding pool applications including low pH, high flow, and heavy use. Save money and energy with 84% thermal efficiency, the highest in its class.
Built by Pentair (Sta-Rite) with a Dura-Glas® rustproof matte black enclosure, compact retrofit design, Low NOx certification, direct Sta-Rite System:3 Mod Media filter compatibility, and the flexibility to convert fuel sources. 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 (HD)
Best-in-class efficiency with heavy-duty cupro nickel tubing for demanding applications.
Cupro Nickel Tubing (HD)
Withstands low pH, high flow, and heavy use — the Max-E-Therm platform's HD upgrade.
Lightest Heater in Its Class
Lightweight design makes installation easier and reduces labor costs.
Compact Retrofit Design
Ideal for retrofit installations where space is limited on an existing equipment pad.
Optional Automatic Bypass
Energy-saving automatic bypass option to 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.
2-Year Warranty
Pentair residential warranty coverage.
Who It's For
- Pool and spa owners who want the Max-E-Therm 400's best-in-class efficiency with added HD durability
- Salt water pools, low pH applications, and high-flow installations that demand cupro nickel tubing
- Retrofit installations where compact footprint is essential
- Anyone who may want 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
| Tubing Material | Cupro Nickel (HD) |
| 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 HD Natural Gas Pool & Spa Heater
- Union Fittings
- User Manual
Warranty
The Max-E-Therm 400 HD 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
What is the difference between the Max-E-Therm 400 (SR400NA) and the 400 HD (SR400HD)?
The Max-E-Therm 400 HD adds cupro nickel tubing to the standard Max-E-Therm 400 platform. Cupro nickel provides significantly better corrosion resistance for low pH, high flow, salt water, and heavy use applications. If your pool has aggressive water chemistry or high bather loads, the HD is the right choice. Both share the same 84% efficiency, Dura-Glas housing, and compact retrofit footprint.
Can I convert this to liquid propane?
Yes. The Max-E-Therm 400 HD can be converted from natural gas to liquid propane by installing a separate LP orifice kit (sold separately).
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.
Is it compatible with salt water pools?
Yes. The cupro nickel tubing in the HD model provides superior resistance to salt water corrosion — making it the recommended choice for salt water pool installations over the standard SR400NA model.