Hayward H400 Pool Heater Propane 400K BTU
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✓ Includes Manufacturer Warranty
✓ Installation Available Upon Request
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The W3H400FDP is a propane pool heater built for in-ground pools and spas on Hayward's Universal H-Series platform. It delivers 400,000 BTU/hr of heating output, runs on low ambient temperatures down to 40 degrees F, and connects via 2" x 2-1/2" CPVC union fittings that make replacement and retrofit installs straightforward. The forced-draft combustion system and low NOx design also qualify it for use in stricter air quality regions including SCAQMD Rule 1146.2 jurisdictions.
W3H400FDP Universal H-Series Gas Pool Heater - Specs and Features
The W3H400FDP runs on 120/240V single-phase, 60 Hz power and draws only 5.5 circuit amps with a 15-amp maximum breaker - a minimal electrical footprint for a 400K BTU unit. It supports water flow between 30 and 125 GPM and uses a cupro nickel heat exchanger rated for salt water and chemically demanding pool environments. The cabinet measures 24" H x 34" W x 29.5" L and weighs 195 lb.
W3H400FDP Installation and Clearance Requirements
The W3H400FDP requires 6 inches of rear clearance and 12 inches on each side. There is no vertical clearance listed, but the forced-draft design eliminates the need for a high-wind stack, which simplifies positioning on tight equipment pads. Plumbing connects via 2" x 2-1/2" CPVC union fittings. Confirm your propane supply line sizing and regulator output match the unit's fuel requirements before setting the pad - gas heaters are sensitive to inlet pressure in ways that heat pumps are not.
Universal H-Series Combustion System and Efficiency
The Universal H-Series platform uses a forced-draft combustion design that pushes air through the chamber at a controlled rate regardless of wind conditions. That removes stack dependency and keeps combustion consistent across installation environments. Hayward's hydraulic design also maintains uniform water velocity across all heat exchanger tubes, which translates to faster heat-up times and reduced pump run time. Hayward rates the efficiency advantage at up to 18% compared with less efficient gas heater designs.
Cupro Nickel Heat Exchanger and Chemical Resistance
The W3H400FDP uses a standard cupro nickel heat exchanger, which handles salt water and aggressive pool chemistry better than standard copper alternatives. For pools running salt chlorine generators or elevated sanitizer levels, this is a meaningful spec - heat exchanger corrosion is one of the more common failure points on gas heaters over time. The cupro nickel material also holds up well in coastal installs where airborne salt adds to the chemical load on the unit.
W3H400FDP Propane Gas Heater vs. Heat Pump - Which Is Right for Your Pool?
Gas heaters like the W3H400FDP heat water faster than heat pumps and maintain full output regardless of air temperature. That makes them the better choice for pools that sit unused for long stretches and need to heat up quickly, or for year-round pools in cold climates where heat pump efficiency drops off. The tradeoff is operating cost: propane burns continuously during use, while heat pumps move heat from the air and use far less energy per BTU delivered in moderate weather. For pools in Florida or similarly warm climates, a heat pump handles day-to-day heating more cheaply, and a gas heater like this one is best used as a primary heater for large pools, spas, or any setup where fast recovery matters more than efficiency.
| Specification | Value |
|---|---|
| Brand | Hayward |
| Model / SKU | W3H400FDP |
| Series | Universal H-Series |
| Fuel Type | Propane (LP) |
| Application | New Construction, Existing Pool or Spa |
| Pool Type | In Ground |
| Heating Capacity | 400,000 BTU/hr |
| Kilowatts | 117 kW |
| Heat Exchanger | Standard cupro nickel |
| Low NOx | Yes |
| Cooling Capability | No |
| Low Ambient Operation | Yes |
| Minimum Operating Temperature | 40 degrees F |
| Voltage | 120/240V |
| Phase | Single |
| Frequency | 60 Hz |
| Circuit Amps | 5.5 |
| Maximum Breaker Size | 15 Amps |
| Water Flow Rate | 30 to 125 GPM |
| Plumbing Connections | 2" x 2-1/2" CPVC union |
| Rear Clearance | 6" |
| Side Clearance | 12" |
| Product Dimensions (H x W x L) | 24" x 34" x 29.5" |
| Product Weight | 195 lb |
| Shipping Dimensions | 30.6" x 32.8" x 39.6" |
| Shipping Weight | 214 lb |
| Refrigerant | No |
| Active Defrost | No |
| Boost Mode | No |
| Silent Mode | No |
| Channel | Open Line |
| GTIN | 610377387279 |
Frequently Asked Questions
Is this unit propane or natural gas?
Propane. The W3H400FDP is configured for LP (liquefied propane) only. If your site runs natural gas, you need the natural gas variant - the two are not interchangeable without a conversion kit, and field conversions should be done by a licensed technician.
What pools and spas is this heater designed for?
In-ground pools and spas. It works on both new construction and existing equipment pads, and the CPVC union connections make it a practical replacement for older H-Series units already plumbed with those fittings.
What electrical service does the W3H400FDP require?
A 120/240V single-phase circuit drawing 5.5 amps, with a 15-amp maximum breaker. For a 400K BTU heater, that is a very small electrical requirement - most of the energy comes from propane, not the grid.
Why does the cupro nickel heat exchanger matter for salt pools?
Salt water is more corrosive to standard copper than to cupro nickel alloy. On a gas heater that runs at high temperatures, exchanger corrosion accelerates faster than on heat pumps, so the material choice has real long-term impact. Cupro nickel holds up better in salt systems and in pools that run higher sanitizer levels.
Does this heater need a special vent stack or chimney?
No. The forced-draft system pushes combustion air through the chamber mechanically, so performance is not dependent on wind or stack height. That said, indoor and semi-enclosed installations still require proper venting - see the indoor vent kit instructions linked below.
Does the W3H400FDP meet low NOx requirements?
Yes. It meets Low NOx clean air standards including SCAQMD Rule 1146.2, which applies in parts of Southern California and some other air quality districts. If your municipality requires low NOx compliance for pool heaters, this model qualifies.
W3H400FDP Warranty, Manuals, and Install Documentation
The W3H400FDP includes a 1-year parts warranty with no labor coverage. Review the installation manual and confirm gas supply, venting, and clearance requirements are met before the unit is started up.
