Hayward H400 Pool Heater Natural Gas 400K BTU
✓ Hayward Authorized Dealer
✓ Includes Manufacturer Warranty
✓ Installation Available Upon Request
✓ 30-Day Return Policy Guarantee
The W3H400FDN is a natural gas 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, operates in low ambient temperatures down to 40 degrees F, and connects via 2" x 2-1/2" CPVC union fittings that simplify replacement and retrofit installs. 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.
W3H400FDN Universal H-Series Natural Gas Pool Heater - Specs and Features
The W3H400FDN ships factory-wired for 240V single-phase, 60 Hz power but can be field-converted to 120V by swapping a jumper on the ignition control board. It 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.
W3H400FDN Installation and Clearance Requirements
The W3H400FDN requires 6 inches of rear clearance and 12 inches on each side. 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. Before setting the pad, confirm your natural gas meter capacity and supply line sizing are sufficient - a 400K BTU heater draws significant gas volume, and undersized piping or a low-capacity meter will cause performance problems at startup.
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 maintains uniform water velocity across all heat exchanger tubes, which produces faster heat-up times and reduces 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 W3H400FDN 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.
W3H400FDN Natural Gas Heater vs. Heat Pump - Which Is Right for Your Pool?
Gas heaters like the W3H400FDN 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: natural gas burns continuously during use, while heat pumps move heat from the air and use far less energy per BTU delivered in moderate weather. Natural gas is generally cheaper to run than propane, which gives the W3H400FDN a cost advantage over the LP version in most markets. For pools in mild climates used regularly, a heat pump handles day-to-day heating more efficiently - but for large pools, spas, or any setup where fast recovery matters more than efficiency, a 400K BTU gas heater is hard to beat.
| Specification | Value |
|---|---|
| Brand | Hayward |
| Model / SKU | W3H400FDN |
| Series | Universal H-Series |
| Fuel Type | Natural Gas |
| Application | New Construction, Renovation |
| 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 (ships 240V; field-convertible to 120V) |
| 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 | 610377387255 |
Frequently Asked Questions
Is this heater natural gas or propane?
Natural gas. The W3H400FDN is configured for natural gas only. If your site runs propane, you need the LP version instead. The two are not interchangeable without a conversion, and that work 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 W3H400FDN require?
It ships wired for 240V single-phase, 60 Hz with a 15-amp maximum breaker, drawing only 5.5 circuit amps. It can be field-converted to 120V by swapping a jumper on the ignition control board - see the installation manual for that procedure. Either way, the electrical draw is minimal for a 400K BTU unit since most of the energy comes from the gas line, 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 installation manual linked below.
Does the W3H400FDN 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.
W3H400FDN Warranty, Manuals, and Install Documentation
The W3H400FDN includes a 1-year parts warranty. Review the installation manual before any work begins to confirm gas supply, venting, and clearance requirements are met at the site.