Best 400K BTU Pool Heaters: Pentair vs Jandy vs Hayward vs Raypak

A 400,000 BTU gas heater can heat a spa quickly and help a larger pool reach a comfortable temperature sooner. But the best heater for your pool depends on more than the number on its label. Gas type, heat-exchanger material, equipment-pad space, automation, local emissions rules, and the heater you are replacing all matter.

Here is a practical comparison of four natural gas heaters in the 400K class that Pool Supply Depot lists: Pentair MasterTemp 400, Jandy JXi 400, Hayward Universal H-Series 400, and Raypak Digital 406A. The Jandy and Raypak models in this comparison are rated at 399,000 BTU input; they belong in the same size class as the 400,000 BTU Pentair and Hayward models.

400K BTU pool heater comparison at a glance

This table compares the exact natural gas listings linked above. Other versions of the same heater family can have different fuel, exchanger, venting, emissions, or commercial certifications. Confirm the full model and part number before ordering.

Pentair MasterTemp 400: A fit for Pentair equipment pads

The Pentair MasterTemp 400, part 460736, combines a compact cabinet, digital controls, and a standard copper heat exchanger. Pentair lists the standard copper model at 84% thermal efficiency. Its optional Smart Heater Bypass Valve Kit can divert water around the heater when it is not firing; that is a separate accessory, not a feature to assume comes in the box.

Choose MasterTemp when you already use Pentair automation or want to keep your equipment within that ecosystem. Check the exact automation interface and installation requirements with your installer. Our linked 460736 product page is marked for in-store information and purchase inquiry; use the listing to confirm availability and buying options rather than assuming online checkout is offered for this model.

Jandy JXi 400: A compact choice for Jandy systems

The Jandy JXi JXI400N is a 399,000 BTU natural gas model with a copper heat exchanger. Jandy describes the JXi family as compact and lists 84% thermal efficiency. This is a useful option when pad space is limited or you are matching an existing Jandy pool and spa control setup.

If reducing pump flow through the heater when it is idle is a priority, ask us about the appropriate Jandy bypass configuration. Do not assume a VersaFlo bypass is included with the standard JXI400N. Jandy also offers a separate JXiQ 400 with VersaFlo listing; confirm which model and included components are right for your installation.

Hayward Universal H-Series 400: Cupro-nickel included

The Hayward Universal H-Series W3H400FDN is a 400,000 BTU natural gas, low-NOx model. Its distinguishing feature in this group is a standard cupro-nickel heat exchanger. Hayward also specifies a forced-draft design and 2-inch by 2½-inch CPVC union connections.

Cupro-nickel can be attractive for owners who want that exchanger material without selecting a different variant. It does not replace proper water balance: incorrect pH, scale, excessive sanitizer, or inadequate flow can damage any heater. If you are replacing an older Hayward heater, ask an installer to check plumbing orientation, gas supply, clearances, and electrical connections before treating it as a direct swap.

Raypak Digital 406A: A straightforward 399K option

The Raypak P-R406A Digital natural gas heater, part 009219, has a 399,000 BTU/h input and a copper heat exchanger. Raypak lists 82% thermal efficiency for its 406A-EN-C digital model. The series offers digital temperature control and is worth considering when replacing a Raypak 406A or when you prefer its control and service layout.

Check the existing heater's complete data plate before ordering. A Raypak 406A can have different fuel, exchanger, header, elevation, and emissions configurations. The linked 009219 is the standard natural gas copper version; it is not an ASME commercial model or automatically the right choice for a jurisdiction with specific low-NOx requirements.

Which 400K BTU heater is best for your pool?

• For a Pentair automation setup: Start with the MasterTemp 460736 and ask about the purchase and installation path.

• For a tight pad or Jandy setup: Compare the JXi JXI400N with the JXiQ if an integrated bypass matters.

• For an included cupro-nickel exchanger: Consider the Hayward W3H400FDN.

• For a Raypak 406A replacement: Review the Raypak 009219, then match its fuel and specifications to the old unit.

There is no universal winner. A correctly matched heater with adequate gas supply, proper water flow, and a compliant installation will serve you better than buying by brand alone.

What to check before buying a 400K BTU gas heater

Natural gas or propane. The four primary models above are natural gas. Order the specified propane version if your property uses LP; do not assume that changing a fitting converts one model to the other.

Gas-line capacity. A 400K-class heater needs sufficient gas pressure and volume under load. Pipe length and other appliances on the same line affect sizing. Have a qualified installer verify the supply before purchase.

Water flow and equipment layout. Check pump and filter capacity, plumbing orientation, bypass requirements, clearances, and whether the heater will be installed outdoors or with approved indoor venting.

Local code and emissions. Low-NOx requirements and installation permits vary by jurisdiction. Verify the exact model's approvals for your location, especially in regulated air districts.

Existing automation and warranty terms. Confirm the heater's control connections, purchase-channel restrictions, and professional installation requirements before ordering. If this is a commercial pool, ask specifically for the appropriate ASME-certified version rather than assuming a residential heater meets the job's specifications.

Frequently asked questions

Is a 400K BTU heater too big for my pool?

Not necessarily. The number describes fuel input per hour, not a minimum pool size. A larger heater may warm a spa or pool faster, but the best size depends on pool volume, desired temperature rise, wind exposure, cover use, gas supply, and equipment design. Get the installation sized for your actual pool.

Will a 400K heater heat a pool twice as fast as a 200K heater?

Under comparable conditions, higher heat output can shorten heat-up time, but real-world results depend on heater efficiency, heat loss, circulation, and whether the gas supply supports the rated input. A pool cover can have a major effect on heat retention.

Is cupro-nickel always required for a saltwater pool?

No blanket rule covers every installation. Cupro-nickel is an option for added resistance in demanding conditions, but proper chemistry, flow, and plumbing matter with either exchanger material. Follow the manufacturer's installation instructions for the specific heater and sanitizer setup.

Can I replace a propane heater with one of these natural gas models?

Only if the property has a suitable natural gas supply and the installation is redesigned and approved for it. Match the fuel shown on the new heater's data plate to the actual supply.

Can Pool Supply Depot help me choose the correct heater?

Yes. Send us a photo of your old heater's complete model/data plate and tell us your fuel type, pool and spa size, automation system, and ZIP code. We can help narrow the options and check the product listing before you order. Pool Supply Depot offers local pickup in Henderson, Nevada, and shipping or freight options for eligible equipment across the United States.

Ready to compare models? View the Pentair MasterTemp 400, Jandy JXi 400, Hayward Universal H-Series 400, and Raypak Digital 406A. Contact Pool Supply Depot with the existing model number for help selecting the correct fuel and configuration.