Pentair Max-E-Therm® 333 HD Natural Gas Pool & Spa Heater 333K BTU
The Pentair Max-E-Therm® 333 HD Natural Gas Pool & Spa Heater 333K BTU brings proven Max-E-Therm performance with heavy-duty cupro nickel tubing — built for demanding 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, optional energy-saving automatic bypass, and direct Sta-Rite System:3 Mod Media filter compatibility. 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 (HD)
Best-in-class efficiency with heavy-duty cupro nickel tubing for demanding applications — the unique 333K BTU size in the Max-E-Therm HD lineup.
Cupro Nickel Tubing (HD)
Withstands low pH, high flow, and heavy use — superior corrosion resistance.
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 whose heat load falls between 200K and 400K BTU wanting HD cupro nickel durability
- Salt water pools, low pH applications, and high-flow installations requiring cupro nickel tubing
- Retrofit installations where the compact Max-E-Therm footprint is essential
- 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
| 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 333 HD Natural Gas Pool & Spa Heater
- Union Fittings
- User Manual
Warranty
The Max-E-Therm 333 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
Why 333K BTU — where does this fit in the lineup?
The Max-E-Therm HD lineup includes 200K, 333K, and 400K BTU sizes. The 333K sits between the 200K and 400K — suited for pools in the 20,000–35,000 gallon range where 200K BTU is insufficient but 400K BTU is more than needed. It's particularly useful when a precise BTU calculation lands in that middle zone.
Can I convert this to liquid propane?
Yes. The Max-E-Therm 333 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 — the recommended choice for salt water pool installations in the Max-E-Therm lineup.
What is the automatic bypass option?
The optional automatic bypass diverts flow around the heater when it's not actively heating, reducing hydraulic resistance and lowering pump energy consumption — an energy-saving add-on for efficiency-focused installations.