Pentair Max-E-Therm® 333 Natural Gas Pool & Spa Heater 333K BTU
The Pentair Max-E-Therm® 333 Natural Gas Pool & Spa Heater 333K 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 — the Max-E-Therm 333 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
333,000 BTU — 84% Efficiency
Rated first in its class for highest energy efficiency at the 333K BTU level.
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.
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 whose heat load falls between 200K and 400K BTU wanting Max-E-Therm efficiency
- Retrofit installations where the compact Max-E-Therm footprint is essential
- Sta-Rite System:3 filter owners who want direct heater integration
- Anyone who may want to switch between natural gas and propane in the future
Specifications
Heating Performance
| BTU Input | 333,000 BTU |
| Thermal Efficiency | 84% |
| Fuel Type | Natural Gas (convertible to LP) |
| Emissions | Low NOx |
| Flow Rate | 33–120 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 333 Natural Gas Pool & Spa Heater
- Union Fittings
- User Manual
Warranty
The Max-E-Therm 333 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 333 (SR333NA) and the 333 HD (SR333HD)?
The Max-E-Therm 333 HD adds cupro nickel tubing to the standard 333 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.
Why 333K BTU — where does this fit in the lineup?
The Max-E-Therm standard lineup includes 200K, 333K, and 400K BTU sizes. The 333K sits between 200K and 400K — suited for pools in the 20,000–35,000 gallon range when a precise BTU calculation lands in that middle zone. It's a common choice for mid-size residential in-ground pools.
Can I convert this to liquid propane?
Yes. The Max-E-Therm 333 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.