Looking for a straight gas pool heater comparison? Pentair MasterTemp, Jandy JXi/JXiQ, Hayward Universal H-Series and Sta-Rite Max-E-Therm are all proven 80%-plus-efficient gas heaters in the 125,000 to 400,000 BTU range. The Pentair ETi is the high-efficiency option, rated up to 96%. The real differences are footprint, heat exchanger material, smart features and how each one fits your pad. Below we compare them side by side and explain how to size one, plus when a heat pump makes more sense.
Quick comparison
| Heater | Sizes (BTU input) | Thermal efficiency (manufacturer) | Heat exchanger | Notable features |
|---|---|---|---|---|
| Pentair MasterTemp | 125K to 400K | 84% (copper); 82% (HD cupronickel) | Copper standard; cupronickel on HD | Certified low NOx, compact, HD and ASME versions, automation-ready |
| Pentair ETi 250 / 400 | 250K, 400K | ETi 400: 96%. ETi 250: 94% natural gas, 96% propane with kit | Direct-fire titanium | High-efficiency, produces condensate, ASME-certified heat exchanger |
| Jandy JXi | 200K, 260K, 399K | 83% (200); 84% (260/400) | Copper or cupronickel options | Low-NOx design, fits a 2' x 2' pad, VersaFlo bypass kit available |
| Jandy JXiQ | 200K, 260K, 399K | 83% (200); 84% (260/400) | Copper or cupronickel; ASME versions in 260/400 | Factory VersaFlo integrated bypass on non-ASME models, Bluetooth diagnostics |
| Hayward Universal H-Series | 150K to 400K | Not listed on product pages | Cupronickel standard | Low NOx (SCAQMD Rule 1146.2), forced draft |
| Sta-Rite Max-E-Therm | 200, 333, 400 models | 84% (copper); 82% (HD cupronickel) | Copper standard; cupronickel on HD | Certified low NOx, HD and ASME versions |
Pentair MasterTemp: the all-around workhorse
The MasterTemp is one of the most common residential gas heaters, and the lineup is wide. Pentair offers it from the small MasterTemp 125, which has 1-1/2" plumbing and is aimed at spas, aboveground pools and inground pools up to 15,000 gallons, all the way up to 400K. Pentair rates the standard copper heat exchanger at 84% thermal efficiency and the heavy-duty (HD) cupronickel version at 82%. It also certifies the heater for low NOx emissions.
- Standard models: MasterTemp 200, 250 natural gas, 250 propane, 300, 400 natural gas and 400 propane.
- HD (cupronickel): the MasterTemp HD 400. Pentair positions HD for low pH, high flow and heavy use. Pentair lists HD models in natural gas only.
- ASME (commercial): MasterTemp ASME 400, ASME 250 propane and ASME HD 400, which combines ASME construction with a cupronickel exchanger.
Pentair also lists a full-text digital display, an ignition control module with flame-strength sensing, and connectivity with Pentair automation. An optional Smart Bypass Valve Kit routes water around the heater when it isn't firing.
Pentair ETi 250 and ETi 400: high-efficiency gas
If the heater will run a lot, the ETi is worth a look. Pentair rates the ETi 400 at 96% thermal efficiency. The ETi 250 is 94% on natural gas and 96% on propane with the conversion kit. Pentair says the ETi 400 can "save up to 14% on energy costs compared to a traditional gas heater." Both use a direct-fire titanium heat exchanger that Pentair describes as corrosion-resistant and ASME certified.
There are trade-offs to plan for:
- Condensate: the ETi produces acidic condensate (Pentair lists pH 3.1 to 4.2), and Pentair offers an optional neutralizer kit.
- Size and weight: the ETi 400 is much larger and heavier than a MasterTemp. Pentair lists it at 379 lbs. The ETi 250 is more compact at 270 lbs.
- Venting and fuel: the ETi 400 uses sealed Category IV direct-vent. Both ship as natural gas and need a Pentair conversion kit for propane.
Pentair notes that the ETi 400's plumbing aligns with the MasterTemp for drop-in replacement.
Jandy JXi and JXiQ: compact, with integrated bypass
Jandy's JXi is known for its small footprint. Jandy says it fits on a 2' x 2' pad and is a MasterTemp or Max-E-Therm replacement that needs no plumbing adjustments. Jandy rates the JXi at 84% thermal efficiency with a low-NOx design. Its catalog lists 83% for the 200 size and 84% for the 260 and 400. Sizes are 200,000, 260,000 and 399,000 BTU. PSW carries the JXi 400 natural gas and the JXi 400 propane low-NOx.
JXi vs JXiQ: what VersaFlo adds
The JXiQ is the newer, smarter version. Its headline feature is VersaFlo integrated bypass, which Jandy says "automatically directs water through the heat exchanger only when heat is needed." On a standard heater, water passes through the heat exchanger even when the burner is off, which adds flow restriction. VersaFlo comes factory-installed on non-ASME JXiQ models. For the JXi, it's available as a kit. Jandy says JXi with VersaFlo can deliver up to 20% additional energy savings.
The JXiQ also adds Bluetooth diagnostics for pros through the Fluidra Pro App, a low gas pressure switch, an estimated time-to-setpoint display, and "Optimize Flow," which measures the inlet-to-outlet temperature rise to help protect the heat exchanger. Homeowner app control through iAquaLink requires Jandy AquaLink automation.
- JXiQ 200 natural gas with VersaFlo
- JXiQ 260 natural gas with VersaFlo
- JXiQ 400 natural gas with VersaFlo and JXiQ 400 propane with VersaFlo
- JXiQ 400 ASME natural gas, cupronickel for commercial jobs
Hayward Universal H-Series: cupronickel as standard
The Hayward Universal H-Series Low NOx line runs from 150,000 to 400,000 BTU. What sets it apart is that Hayward makes a cupronickel heat exchanger standard, not an upgrade. Hayward says it has excellent resistance to salt water and chemical corrosion. Hayward states the H-Series meets or exceeds the South Coast Air Quality Management District (SCAQMD Rule 1146.2) low NOx standard. Its forced-draft system moves air through the combustion chamber at a set rate. That's a good fit for saltwater pools and Hayward-equipped pads. See the Universal H-Series 250 natural gas or browse Hayward equipment.
Sta-Rite Max-E-Therm and Max-E-Therm HD
Sta-Rite is a Pentair brand, and the Max-E-Therm shares a lot of DNA with the MasterTemp. Pentair's literature lists 84% efficiency for the standard and ASME copper heat exchangers and 82% for the HD cupronickel version, with low NOx certification. Models come in 200, 333 and 400 sizes. Many pros stick with Max-E-Therm to match an existing pad. Options include the Max-E-Therm 400 natural gas and the Max-E-Therm 400 HD (cupronickel).
Gas heater vs heat pump
A gas heater burns fuel and heats quickly no matter the air temperature. That makes it ideal for spas, quick weekend heat-ups and cool-season swimming. A heat pump like the Hayward HeatPro 140K runs on electricity and moves heat from the air into the water. It's slower, but it often costs less to run for holding a steady temperature in warm weather. Hayward rates HeatPro output at 80°F air and lists noticeably lower output at 50°F air, so heat pumps lose capacity as it gets colder. Many owners in warm climates use a heat pump for season-long swimming. Many spa owners, and anyone heating on demand, choose gas. Compare both in our pool heaters and heat pumps collection.
How to size a gas pool heater (BTU)
The U.S. Department of Energy publishes a common sizing formula:
BTU/hr output = pool surface area (sq ft) × temperature rise (°F) × 12
Temperature rise is your desired pool temperature minus the average air temperature for the coldest month you plan to swim. The DOE notes the formula assumes a 1° to 1-1/4°F rise per hour and a 3-1/2 mph average wind at the pool surface.
Example: a 16' x 32' pool has 512 sq ft of surface. To hold 82°F when the coldest month averages 62°F, you need a 20°F rise: 512 × 20 × 12 = 122,880 BTU/hr of output. Heater ratings are input, and an 84%-efficient heater delivers about 84% of its input as heat. That puts this pool around 146,000 BTU input at minimum. Most owners step up to a 250K or 400K for faster heat-up. Jandy's own sizing chart is a useful cross-check. At a 30°F difference with no wind, Jandy lists the 200 for up to 490 sq ft, the 260 for 640 sq ft and the 400 for 990 sq ft.
Wind, shade and especially a pool cover change the math. DOE estimates show covers dramatically cut heating costs. When in doubt, the DOE recommends having a pool professional do a proper sizing analysis.
Key buying factors
Natural gas vs propane
Heaters are built for one fuel, so order the right version (for example, MasterTemp 400 natural gas vs propane). Some models, like the ETi, ship as natural gas and convert with a manufacturer kit. Propane carries more energy per cubic foot than natural gas, but it's typically delivered to an on-site tank that must be sized for the heater's demand. Which fuel costs less to run depends on your local rates.
Low NOx
"Low NOx" means lower nitrogen-oxide emissions. Some air districts, such as Southern California's SCAQMD, require it. MasterTemp, JXi, H-Series and Max-E-Therm are all marketed as low NOx, but confirm that the specific model meets your local air-quality rule.
ASME for commercial pools
ASME models are built to American Society of Mechanical Engineers boiler and pressure-vessel standards, usually with bronze or brass headers. Commercial and public pools often require ASME-certified heaters, so check with your local health department or code official. See our commercial pool equipment.
Copper vs cupronickel heat exchangers
Copper transfers heat well and is standard on most residential heaters. Cupronickel (copper-nickel) holds up better to low pH, high flow, heavy use and salt. That's why Pentair uses it on HD models and Hayward makes it standard on the H-Series. The trade-off is a small efficiency difference: Pentair lists 82% for HD versus 84% for copper. If you run a salt system or water chemistry is hard to keep balanced, cupronickel is cheap insurance. Balanced water still matters with either material.
Gas line sizing, installer and permits
An undersized gas line is one of the most common causes of poor heater performance. Required pipe size depends on BTU input, fuel type and run length. For example, Jandy's chart allows only about 15 ft of 3/4" pipe for a JXi 400 on natural gas, and each elbow adds equivalent length. Gas piping, venting and electrical connections should be handled by a licensed installer, and most areas require a permit and inspection. Follow the installation manual and local codes.
Freight delivery
Gas heaters ship by freight truck, not parcel. Plan for someone to receive and inspect the delivery. Details are on our shipping and freight page.
How to choose the right heater
- Spa, aboveground or small pool (up to about 15,000 gallons): MasterTemp 125 or a 200K model.
- Typical residential inground pool: MasterTemp 250 to 400, JXi/JXiQ 260 or 400, or H-Series 250 to 400. A 400K is the popular choice when a spa is attached.
- Tight equipment pad or retrofit: JXi/JXiQ for the compact footprint, or match what's there (MasterTemp, Max-E-Therm) for the easiest swap.
- Saltwater pool: a cupronickel heater, such as H-Series, MasterTemp HD, Max-E-Therm HD or JXiQ cupronickel.
- Heavy use, lowest fuel per BTU: ETi 250 or 400, if the pad, venting and condensate can be accommodated.
- Commercial or HOA pool: ASME models such as MasterTemp ASME or JXiQ ASME.
- Warm climate, steady temperature all season: consider a heat pump, or pair one with a gas heater for the spa.
FAQ
Is the Jandy JXi or Pentair MasterTemp better?
Both are reliable and use the same efficiency class (low 80s percent). JXi/JXiQ wins on footprint and integrated bypass. MasterTemp offers more sizes, plus HD and ASME versions, and integrates neatly with Pentair automation. Match the heater to your pad and automation brand.
What size gas heater do I need for my pool?
Use surface area × temperature rise × 12 for the BTU/hr output (DOE formula), then allow for heater efficiency. Most inground pools land between 250K and 400K. At the same efficiency, a bigger heater mainly heats faster rather than costing more per degree.
Can I convert a natural gas heater to propane?
Some models can be converted with a manufacturer kit (Pentair offers kits for the ETi). Others are sold as separate natural gas and propane versions. Conversions should be done by a qualified gas technician.
Do I need a cupronickel heat exchanger for a salt pool?
It isn't always required, but manufacturers like Hayward highlight cupronickel's resistance to salt water and chemical corrosion. Check the manufacturer warranty terms for salt pools.
What does ASME mean on a pool heater?
The heater is built to American Society of Mechanical Engineers standards. It's commonly required for commercial and public pools, rarely for residential.
Gas heater or heat pump: which is cheaper to run?
It depends on your gas and electric rates and your climate. Heat pumps are typically cheaper for holding temperature in warm weather. Gas is faster and works in any air temperature.
Need help picking a size or matching a heater to an existing pad? Contact our team or call 855-677-7796. Contractors can ask about wholesale and commercial pricing. Browse every model in our pool heaters and heat pumps collection.
Specs from manufacturer documentation as of 2026; always confirm with the product manual and local codes.