{"product_id":"hayward-hdf400-universal-hc-pool-spa-heater-400k-btu-dual-fuel-energy-efficient-low-nox","title":"Hayward HDF400 Universal HC Pool \u0026 Spa Heater – 400K BTU Dual-Fuel, Energy-Efficient, Low NOx","description":"\u003cp data-start=\"488\" data-end=\"827\"\u003eThe \u003cstrong data-start=\"492\" data-end=\"541\"\u003eHayward HDF400 Universal HC Pool \u0026amp; Spa Heater\u003c\/strong\u003e delivers \u003cstrong data-start=\"551\" data-end=\"589\"\u003epowerful, energy-efficient heating\u003c\/strong\u003e with a \u003cstrong data-start=\"597\" data-end=\"619\"\u003e400,000 BTU output\u003c\/strong\u003e, making it ideal for large residential pools and spas. Featuring a \u003cstrong data-start=\"687\" data-end=\"707\"\u003edual-fuel design\u003c\/strong\u003e, this heater provides flexible installation options while maintaining \u003cstrong data-start=\"778\" data-end=\"824\"\u003ereliable and consistent water temperatures\u003c\/strong\u003e.\u003c\/p\u003e \u003cp data-start=\"829\" data-end=\"1162\"\u003eEngineered with \u003cstrong data-start=\"845\" data-end=\"867\"\u003elow NOx technology\u003c\/strong\u003e, the HDF400 meets strict emissions standards without sacrificing performance. Its \u003cstrong data-start=\"950\" data-end=\"979\"\u003ecompact, universal design\u003c\/strong\u003e allows for easy replacement of existing heaters, while the \u003cstrong data-start=\"1039\" data-end=\"1070\"\u003ecupro-nickel heat exchanger\u003c\/strong\u003e ensures superior durability and corrosion resistance—even in demanding pool environments.\u003c\/p\u003e \u003ch2 data-start=\"1169\" data-end=\"1191\"\u003e\u003cstrong data-start=\"1172\" data-end=\"1189\"\u003e\u003cmeta charset=\"utf-8\"\u003e \u003cstrong data-start=\"492\" data-end=\"541\"\u003eHayward HDF400 Universal HC Pool \u0026amp; Spa Heater \u003c\/strong\u003eCompatibility\u003c\/strong\u003e\u003c\/h2\u003e \u003cul data-start=\"1192\" data-end=\"1439\"\u003e \u003cli data-start=\"1192\" data-end=\"1249\"\u003e \u003cp data-start=\"1194\" data-end=\"1249\"\u003eDesigned for \u003cstrong data-start=\"1207\" data-end=\"1247\"\u003ein-ground residential pools and spas\u003c\/strong\u003e\u003c\/p\u003e \u003c\/li\u003e \u003cli data-start=\"1250\" data-end=\"1311\"\u003e \u003cp data-start=\"1252\" data-end=\"1311\"\u003eCompatible with \u003cstrong data-start=\"1268\" data-end=\"1309\"\u003enatural gas or propane configurations\u003c\/strong\u003e\u003c\/p\u003e \u003c\/li\u003e \u003cli data-start=\"1312\" data-end=\"1376\"\u003e \u003cp data-start=\"1314\" data-end=\"1376\"\u003eWorks with \u003cstrong data-start=\"1325\" data-end=\"1374\"\u003estandard pool plumbing and electrical systems\u003c\/strong\u003e\u003c\/p\u003e \u003c\/li\u003e \u003cli data-start=\"1377\" data-end=\"1439\"\u003e \u003cp data-start=\"1379\" data-end=\"1439\"\u003eIntegrates with \u003cstrong data-start=\"1395\" data-end=\"1437\"\u003eHayward automation and control systems\u003c\/strong\u003e\u003c\/p\u003e \u003c\/li\u003e \u003c\/ul\u003e\u003ch2\u003eKey Features\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eSupplied under part number HDF400 for exact-match ordering.\u003c\/li\u003e\n\u003cli\u003eBTU rating: 400K BTU.\u003c\/li\u003e\n\u003cli\u003eSized by BTU output — match the rating and fuel type to your existing unit.\u003c\/li\u003e\n\u003cli\u003eShips from our US warehouse with tracking on dispatch.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eSpecifications\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Hayward\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer part number:\u003c\/strong\u003e HDF400\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCategory:\u003c\/strong\u003e Pool Heaters\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCondition:\u003c\/strong\u003e New\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBTU rating:\u003c\/strong\u003e 400K BTU\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eShipping weight:\u003c\/strong\u003e 183 lb\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003ch3\u003eWhat part number is this pool heater?\u003c\/h3\u003e\u003cp\u003eThis item is supplied under part number HDF400. Match that number against your equipment's parts diagram before ordering.\u003c\/p\u003e\u003ch3\u003eDoes the BTU rating have to match my old heater?\u003c\/h3\u003e\u003cp\u003eThe BTU rating should match or exceed your previous heater. Undersizing means the pool never reaches temperature on cold days; oversizing costs more up front but heats faster and cycles less.\u003c\/p\u003e\u003ch3\u003eCan this run on propane instead of natural gas?\u003c\/h3\u003e\u003cp\u003eNo. Gas pool heaters are built for one fuel and require a manufacturer conversion kit to change. Check the data plate on your existing unit and order the matching fuel type.\u003c\/p\u003e\u003ch3\u003eWhat size heater do I need for my pool?\u003c\/h3\u003e\u003cp\u003eA common rule is 1 BTU per gallon as a minimum, increased for windy sites, uncovered pools, or cold climates. A 20,000 gallon pool typically starts at 250,000 BTU.\u003c\/p\u003e\u003ch3\u003eDo I need a professional to install a pool heater?\u003c\/h3\u003e\u003cp\u003eGas heaters involve gas line sizing, venting and electrical connections, and most jurisdictions require a licensed installer plus a permit. Improper installation voids the manufacturer warranty.\u003c\/p\u003e\u003ch3\u003eHow do I confirm this part fits my equipment?\u003c\/h3\u003e\u003cp\u003eCheck the part number stamped on the component you are replacing, or find it on the parts schematic in your owner's manual. If the number differs or is unreadable, send us your equipment model and serial number and we will verify fitment before you order.\u003c\/p\u003e\u003ch3\u003eHow quickly does this ship?\u003c\/h3\u003e\u003cp\u003eIn-stock items ship from our US warehouse on business days. You will receive tracking by email once the order leaves the warehouse.\u003c\/p\u003e\u003ch3\u003eCan I return it if I ordered the wrong part?\u003c\/h3\u003e\u003cp\u003eUnopened, uninstalled items can be returned within 30 days. Equipment that has been installed or plumbed cannot be returned, so confirm fitment before installation.\u003c\/p\u003e\u003ch3\u003eIs this covered by a warranty?\u003c\/h3\u003e\u003cp\u003eManufacturer warranty terms vary by brand and product. Warranty claims generally require proof of purchase and, on installed equipment, evidence of professional installation.\u003c\/p\u003e\u003cscript type=\"application\/ld+json\"\u003e{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"What part number is this pool heater?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"This item is supplied under part number HDF400. 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