Jandy JXi Pool & Spa Heater — 399,000 BTU/h Natural Gas | JXI400N

399,000 BTU/h input; Natural Gas; 84% thermal efficiency; copper heat-exchanger tubes / polymer headers; 30–100 GPM; 50 PSI maximum working water pressure; 2-inch water connections; cabinet dimensions in Width × Depth × Height order: 21.6 × 22.1 × 26.5 inches (excludes vent/header/plumbing projections and required installation clearances); 126 lb manufacturer-listed product weight.

The heater, one Versa Plumb sweep elbow, two 2-inch union tailpieces, one union cap, three union O-rings and three union nuts as listed in the standard-header package table; one cap/O-ring/nut set is preinstalled at the horizontal inlet. Factory VersaFlo is not identified by this ordering code. The standard heater is not supplied with a pressure-relief valve; approved venting, gas/electrical connections and other field materials are separate.

Choose JXI400N for its natural gas supply, 399,000 BTU/h input, copper heat exchanger and polymer header. This is the standard polymer-header configuration; it is not the ASME bronze-header model. Heater sizing depends on the pool/spa, climate and required heating conditions, not BTU input alone.

Factory wired for 240 VAC, 60 Hz; 120 VAC conversion is described in Section 6.3 of the JXi manual and must be performed by a qualified professional. This JXi model does not use the JXiQ auto-sensing electrical arrangement.

The manufacturer specifies 30–100 GPM through the heater. A manual external bypass is required when pump flow exceeds the allowed maximum. The internal thermal-regulator/bypass arrangement is not a factory VersaFlo feature on this ordering code. Maximum working water pressure is 50 PSI for this polymer-header configuration. Flow, relief protection and the pressure limits of all system components must be checked together.

The manufacturer lists a 8-inch Category I connection for model size 400 and a 4-inch Category III connection. A vent adapter alone is not a complete approved venting system. Natural-gas installation classifications include indoor, outdoor and covered-shelter use when all specified provisions are met. A qualified installer must verify combustion air, vent type, equivalent length, termination, clearances, gas supply and local requirements.

The cabinet/body dimensions are 21.6 inches wide × 22.1 inches deep × 26.5 inches high. The Dimensions field lists those three values in that order. Vent, header and plumbing projections, the supporting pad and service/combustible clearances are additional. Use the drawing for the exact installed revision; body dimensions are not the total installed footprint. Manufacturer-listed product weight is 126 lb; shipping/package measurements are separate.

The JXi has a local digital control panel and supports the control connections described in its manual. Compatible external automation is separately installed; an internet connection or app controller is not implied by this heater ordering code.

The R0731100 4-inch exhaust adapter and R0724600 3-inch intake kit are separate installation accessories; JXIGUARD is a separate control-panel lock box. The standard polymer-header relief-valve kit is R0336101 (50 PSI), separate from the ASME 75 PSI kit. Confirm header revision and kit instructions before retrofitting an anode to an older JXi.

Jandy’s current limited warranty excludes equipment purchased through the internet or an e-commerce site, apart from the stated exceptions for parts, pool accessories and valves under 3 inches. This complete heater is not a replacement-part exception. The general heater/commercial terms do not establish an unconditional warranty for an online heater purchase. Review the full manufacturer statement before purchase. Qualified licensed installation/service where required, first-retail-purchaser/original-site limits, geography and the stated exclusions apply.

Use the JXi Installation & Operation Manual, JXi exact-model sell sheet, 2026 heater ordering table and current Jandy Limited Warranty, H0333803 Rev AB. The manufacturer EnergyGuide index identifies the appropriate 84% label. Follow the exact model, header, fuel and installed revision.