Hayward Universal H-Series 400K BTU Natural Gas Heater | H400FDN

Product Overview The Hayward Universal H-Series H400FDN Natural Gas Heater is a high-performance pool and spa heater designed to deliver fast, reliable heating for compatible residential pool and spa systems. With a powerful 400,000 BTU heating capacity, this heater is built for customers who need strong heat output, faster temperature recovery, and dependable operation from a trusted pool equipment brand. This model operates on natural gas and is intended for outdoor pool equipment pad installations with compatible plumbing, gas supply, electrical service, water flow, venting clearances, and equipment layout. Because heater sizing and installation requirements depend on pool size, spa size, gas line capacity, plumbing flow, and local code, this product should be installed by a qualified pool professional and licensed gas technician. Ideal For Residential swimming poolsPool and spa combination systemsSpas requiring faster heat-up timesReplacing compatible Hayward H-Series natural gas heatersCustomers needing high BTU heating capacityOutdoor pool equipment pad installationsPool owners who want faster heating than most heat pump applicationsPool professionals installing Hayward gas pool heaters What’s Included Hayward Universal H-Series H400FDN natural gas heaterFactory-installed heat exchanger and internal componentsDigital control interfaceNatural gas burner systemOutdoor-rated heater cabinetManufacturer-supplied installation documentation and packaging What’s Not Included Installation laborGas line or gas line upgradesGas shutoff valveGas regulator unless required or supplied separatelyElectrical wiring materialsBreaker or disconnectPlumbing fittings or unions unless included by manufacturer packagingExternal bypass plumbingVent kit or indoor venting componentsAutomation systemPool coverProfessional startup service Compatibility Guidance The Hayward H400FDN is designed for compatible pool and spa systems that require a 400K BTU natural gas heater and have the correct gas, plumbing, electrical, and water-flow setup. Before ordering, confirm the following: You need part number H400FDN.Your site has natural gas, not propane.Your gas meter and gas line can support a 400,000 BTU heater.Your pool or spa size and heating expectations match a 400K BTU gas heater.Your pump and filter system can provide the required water flow.Your plumbing layout can support proper heater installation and service access.Your installation location meets required clearances for outdoor heater operation.Your water chemistry can be maintained within heater-safe ranges.Your installer has confirmed gas, plumbing, electrical, and code compatibility. Do not order this heater by BTU rating alone. Gas type, gas line capacity, plumbing flow, installation location, electrical requirements, and local code must all be verified before purchase. Confirm Before Ordering Before purchasing, please verify: You need the Hayward H400FDN model.You need a natural gas heater, not propane.Your site has adequate natural gas supply for 400,000 BTU operation.Your pool or spa system is properly sized for a 400K BTU heater.Your equipment pad has proper clearance around the heater.Your pump and filter system can provide proper water flow.Your installation meets local gas, plumbing, electrical, and safety code requirements.Professional installation will be completed by a qualified pool professional and licensed gas technician. Key Features Genuine Hayward Universal H-Series heaterModel H400FDN400,000 BTU heating capacityNatural gas fuel typeDesigned for compatible residential pool and spa systemsFast heat-up and strong temperature recoveryDigital control interfaceUniversal-fit design for flexible installation layoutsCupro nickel heat exchanger for added corrosion resistanceLow NOx emissions designOutdoor-rated heater cabinetProfessional installation required Benefits The Hayward Universal H-Series H400FDN is built for pool and spa owners who need powerful heating performance. Its 400K BTU output can heat compatible pools and spas faster than many lower-output heaters and is especially useful for spas, pool/spa combinations, and customers who want quicker temperature recovery. Natural gas heating is a strong choice for customers who want on-demand heat and reliable performance across a wider range of outdoor air temperatures compared with many heat pumps. The Universal H-Series design also offers installation flexibility, making it useful for both new equipment pads and compatible heater replacement projects. Natural Gas Heater vs. Heat Pump A natural gas heater burns natural gas to create heat quickly. It is often preferred when fast heat-up is important, especially for spas, pool/spa combinations, or pools used on demand. A heat pump uses electricity to transfer heat from the surrounding air into the pool water. Heat pumps are often selected for efficient temperature maintenance over time but may heat more slowly and are affected by outdoor air temperature. Choose the Hayward H400FDN natural gas heater if your priority is fast heating and your site has the proper natural gas service for a 400K BTU heater. Recommended Use Use the Hayward Universal H-Series H400FDN for compatible residential pool and spa systems where a 400K BTU natural gas heater is properly sized for the pool volume, spa volume, plumbing flow, and heating goals. This model is especially useful for customers who want quick spa heat-up, faster pool temperature recovery, or dependable gas heat for a pool/spa combination. For sites without natural gas service, or where gas line capacity is not sufficient, a propane model, heat pump, or different heater size may be needed. Installation Notes This heater should be installed by a qualified pool professional and licensed gas technician. Gas pool heater installation may involve gas line sizing, gas pressure verification, electrical wiring, bonding, grounding, plumbing connections, water-flow verification, combustion air clearance, venting requirements, and startup testing. Professional installation is required to ensure: Correct gas type confirmationProper gas line sizing and pressureCorrect electrical wiringProper bonding and groundingCorrect plumbing connection and water flowAdequate clearance around the heaterSafe combustion and exhaust clearanceLeak-free plumbing and gas connectionsCorrect startup and temperature programmingCompatibility with automation and pool controls Improper installation may cause heater failure, gas leaks, fire hazard, carbon monoxide risk, electrical hazards, water leaks, poor heating performance, or voided warranty coverage. Important Gas & Safety Note This model is for natural gas only. It should not be connected to propane. Gas heater installation must follow manufacturer instructions, local code, and all applicable safety requirements. Always verify gas type, gas pressure, and line capacity before installation. Technical Specifications Specification Details Brand Hayward Product Line Universal H-Series Model / Part Number H400FDN Product Type Pool & Spa Gas Heater Heating Capacity 400,000 BTU Fuel Type Natural Gas Voltage Verify installation requirements before publishing Application Pool and Spa Heating Installation Type Outdoor Pool Equipment Pad Control Type Digital Control Interface Heat Exchanger Cupro Nickel Low NOx Yes Complete Heater Included Yes Propane Compatible No Gas Line Included No Pool Cover Included No Professional Installation Required Yes SKU H400FDN UPC / Barcode 0610377027250 Customer-Facing Q&A Q: What size is the Hayward H400FDN heater?A: This model is rated at 400,000 BTU. Q: Is this natural gas or propane?A: This model is natural gas only. It is not a propane heater. Q: Can this heater be converted to propane?A: Do not assume field conversion is available. Order the correct fuel type for your installation and follow Hayward instructions and local code. Q: Is this a complete heater?A: Yes. This is the complete Hayward Universal H-Series natural gas heater. Q: Is this good for spas?A: Yes. A 400K BTU gas heater is commonly used for spas and pool/spa combinations where faster heat-up is desired, provided the system is properly sized and installed. Q: Does this include installation materials?A: Basic manufacturer packaging is included, but gas piping, electrical materials, plumbing fittings, unions, venting components, and labor are not included unless specifically stated. Q: Does this require a gas line?A: Yes. This heater requires a properly sized natural gas line and gas supply capable of supporting a 400K BTU heater. Q: Can I install this myself?A: No. Professional installation by a qualified pool professional and licensed gas technician is required. Q: What should I check before ordering?A: Confirm that you need H400FDN, that your site uses natural gas, that your gas line can support 400,000 BTU, and that your plumbing and electrical setup are compatible. Q: Is this better than a heat pump?A: It depends on your goal. Gas heaters heat faster and are ideal for on-demand heating, while heat pumps are often used for efficient temperature maintenance over time.