Hayward Universal H-Series H400FDN Gas Pool Heater
A large Florida pool, or a pool and spa combination, that needs to reach temperature on demand rather than hold it all season.
Gas heater
SKU H400FDN
- BTU input
- 399,900 BTU/hr
- Fuel / power
- Natural gas
- Thermal efficiency
- 84% thermal efficiency
- Heat exchanger
- Cupro-nickel
- Warranty
- Parts: 3 years · Labor: 1 year field labor (3 years when sold by a Hayward Rewards dealer)
- Controls & automation
- Onboard control pad with a two-digit temperature display and separate pool and spa setpoints; app control when connected to a Hayward Omni control system.
Modern Pool Heating Equipment Score
Our score for the equipment itself. It is not a Google or customer review rating.
How we rate heatersFull specifications
Every row below is taken from a manufacturer document. Anything the manufacturer does not publish is left out rather than estimated.
| Manufacturer product name | Universal H-Series Heater 400,000 BTU - Natural Gas, Low NOx |
|---|---|
| BTU input | 399,900 BTU/hr (marketed as 400,000 BTU) |
| Thermal efficiency | 84% |
| Fuel | Natural gas (H400FDP is the propane version) |
| Heat exchanger | Cupro-nickel, standard on all models |
| Emissions | Low NOx; meets SCAQMD Rule 1146.2 |
| Water connections | 2" x 2-1/2" CPVC unions |
| Gas connection | 3/4" NPT |
| Water flow | 30 GPM minimum, 125 GPM system maximum |
| Gas pressure (natural gas) | 4.5" w.c. minimum inlet, 10.5" w.c. maximum inlet, 2.0" w.c. manifold |
| Indoor vent pipe | 6" diameter (natural gas) |
| Clearances | 6" rear, 12" sides |
| Minimum operating temperature | 40°F |
| Electrical | Field-selectable voltage plug: 110-130 VAC, 2 A or 220-250 VAC, 1 A (240 VAC factory default). Hayward's product page lists 120/240V, 1 phase, 60 Hz, 5.5 circuit amps, 15 A maximum breaker. |
| Cabinet width | 34" (24" H x 29.5" L) |
| Certification | Certified by the Canadian Standards Association |
| Controls and automation | Onboard control pad with protective cover, two-digit temperature display, separate pool (90°F default maximum) and spa (104°F default maximum) setpoints; controllable from the Omni app when connected to a Hayward Omni control system. |
Why homeowners consider it
- The cupro-nickel heat exchanger is standard on every model in the line rather than a paid upgrade, which matters on salt pools and coastal installs where a plain copper exchanger is the first thing to go.
- At 84% thermal efficiency it sits at the top of Hayward's own published table for the Universal H-Series, level with the 250,000 BTU model and ahead of the 500,000 and the smaller units.
- 399,900 BTU/hr of input is enough to bring a large pool up in an afternoon and more than enough to run an attached spa, which is the job gas does better than anything else. Hayward's table puts it at about 18 minutes to raise a 400-gallon spa by 30°F.
- Service access is from the front panel only, so a tech is not pulling the unit away from the wall to reach the board — a real advantage on the tight equipment pads common in Sarasota side yards.
- Universal 2 inch by 2.5 inch CPVC union connections and junction boxes on both sides make it straightforward to drop into an existing pad without re-plumbing everything around it.
What to know before buying
- Natural gas has to actually be available at your address. Large parts of Sarasota and Manatee County have no gas main, which pushes you to the propane version (H400FDP) plus a tank and a delivery contract.
- This is a 399,900 BTU/hr appliance with a 3/4 inch NPT gas connection, and the gas line back to the meter has to be sized for it. An undersized existing line is the most common reason a gas heater swap turns into a bigger job than the quote.
- Hayward specifies 6 inches of rear clearance and 12 inches on the sides, and a minimum operating temperature of 40°F. The cabinet is 34 inches wide — nine inches wider than the H250 — so check the clearances and the pad against your space before ordering.
- It needs a minimum of 30 GPM through the heat exchanger, with a 125 GPM system maximum. On a variable-speed pump that means the heating speed has to be set high enough to satisfy the flow switch.
- The labor side of the warranty depends on who sells it. Hayward's 2026 Expert Line residential terms give 1 year of field labor as standard and 3 years when the heater is sold by a Hayward Rewards dealer, and the W3-prefixed version sold online is an Open Line SKU with 1 year parts and no labor — worth confirming with whoever quotes you.
- Hayward's sizing recommendations assume a 30°F temperature rise, 3.5 mph average wind and an elevation up to 2,000 feet. Screen enclosures, exposure and how warm you actually want the water will move the real-world result.
Warranty, term by term
The warranty only matters on the parts that actually fail. Here is how this one splits up.
- Parts
- 3 years
- Labor
- 1 year field labor (3 years when sold by a Hayward Rewards dealer)
Hayward's 2026 Expert Line residential terms cover in-ground products at 3 years parts and 1 year field labor as standard, extended to 3 years field labor when the heater is sold by a Hayward Rewards dealer (the program formerly branded Totally Hayward). There is no separate longer heat-exchanger term — the cupro-nickel exchanger is covered under the parts warranty as original equipment, while a heat exchanger bought later as a replacement part carries 1 year parts only with no labor. Heating elements and o-rings are treated as normal wear items. Hayward states its limited warranties apply only to product bought from Hayward or a Hayward authorized seller, and the W3-prefixed version of this heater is an Open Line SKU carrying 1 year parts only with no labor coverage. Professional installation and authorized-channel requirements may apply. The commercial ASME variant has its own warranty document, which we have not verified.
Why the heat exchanger matters
The heat exchanger is the part of a pool heater that actually moves heat into the water, and what it is made of decides how long the heater survives Florida water chemistry. Here is what the four materials mean in practice.
- Copper
- The traditional material and the cheapest to build. It transfers heat well and is fine on a well-balanced chlorine pool, but it is the least forgiving of low pH, high chlorine and salt. On the Gulf Coast it is usually the first component to fail.
- Cupro-nickelThis heater
- Copper alloyed with nickel. It gives up a little heat transfer in exchange for much better resistance to unbalanced water chemistry and salt. On gas heaters this is the upgrade worth having in Florida, and some manufacturers now ship it as standard.
- NiTek (nickel alloy)
- A nickel-alloy exchanger used on some gas heaters as a corrosion-resistant alternative to copper. Positioned between cupro-nickel and titanium in both durability and price.
- Titanium
- Effectively immune to pool water chemistry, including salt. It is the standard on quality pool heat pumps and the reason a heat pump can sit on a salt pool for years without exchanger trouble. It is expensive, which is why you rarely see it on gas heaters.
Whatever the material, plumbing order matters just as much: a chlorinator or salt cell belongs downstream of the heater, never upstream.
How we scored it
- Warranty is 3 years parts and 1 year field labor as standard, against 2 years parts and labor on Pentair's MasterTemp and 1 year parts with no labor on Jandy's JXi, and up to 3 years of field labor is available through a Hayward Rewards dealer. Not a 5, because both the labor term and Open Line eligibility depend entirely on where you buy it.
- Durability scores high because cupro-nickel is standard across the line. On the Gulf Coast that is the single most useful thing about this heater.
- 84% thermal efficiency is at the top of Hayward's own published table for the line.
- Serviceability is a strength: front-panel-only access, universal plumbing unions, a published consumer troubleshooting guide with the full diagnostic code list, and parts that are stocked widely in Florida.
- Controls lose a point for being tied to Hayward's own Omni system for app control rather than carrying the embedded OmniX control that the HS400FDN has.
- Value is a 5: the corrosion-resistant exchanger that competitors charge extra for is included, which is exactly what you are paying the upper-mid price tier for.
Real Modern Pool Heating installations
Installed locally, researched for everyone
Affordable Solar & Pool Heating, LLC installs and services pool heating in Sarasota, Manatee, Charlotte & Pinellas County, Florida. If you are outside that area this page is still yours to use — take the questions on it to your local contractor. Pool heater installation in Sarasota.
Other heaters worth putting beside it
Same job, different tradeoffs. Every one of these has its own verified spec page.
Pentair · MasterTemp
Pentair MasterTemp 400 NG Gas Pool Heater
Model MasterTemp 400 NG
- BTU input
- 400,000 BTU/hr
- Thermal efficiency
- 84%
- Heat exchanger
- Copper
- Warranty
- 2-Year Parts & Labor
- Wi-Fi / automation
- Automation Compatible
A large pool, or a pool and spa combination, on a pad that is already Pentair and an owner who wants heat on demand rather than an everyday running cost.
Jandy · JXi
Jandy JXi400N Gas Pool & Spa Heater
Model JXI400N
- BTU input
- 399,000 BTU/hr
- Thermal efficiency
- 84%
- Heat exchanger
- Copper
- Warranty
- 1-Year Parts
- Wi-Fi / automation
- App Control via AutomationAutomation Compatible
A large Gulf Coast pool, or a pool and spa combination, where the spa needs to be ready in under an hour and the equipment pad has no room to spare.
Raypak · AVIA
Raypak AVIA 404A Gas Pool & Spa Heater
Model P-R404A-EN-C
- BTU input
- 399,000 BTU/hr
- Thermal efficiency
- 84%
- Heat exchanger
- Copper
- Warranty
- 3-Year Parts & Labor
- Wi-Fi / automation
- Wi-Fi Built InAutomation Compatible (Relay)
A large Florida pool, or a pool and spa, where the owner wants spa-speed output and three years of parts and labor cover.
H400FDN questions
What size pool is a 400,000 BTU heater right for?
It is a large-pool and pool-plus-spa heater. Hayward's own sizing guidance assumes a 30°F temperature rise at 3.5 mph average wind, but surface area, whether the pool is screened and how fast you want it to heat matter more than volume. We size it against the pool before quoting rather than from a chart.
What is the difference between H400FDN and H400FDP?
Fuel. The N is the natural gas version and the P is the propane version. They are otherwise the same heater, though the indoor vent pipe diameter and gas pressure requirements differ — propane wants 10 to 13 inches w.c. at the inlet against natural gas's 4.5 to 10.5.
Is this heater safe on a salt water pool?
The cupro-nickel heat exchanger is standard on every Universal H-Series model and Hayward describes it as offering excellent salt water and chemical corrosion resistance. As with any heater, the salt cell or chlorinator has to be plumbed downstream of the heater, never upstream.
Does it work with pool automation?
Yes. Hayward states the heater can be controlled from the Omni app when connected to a Hayward Omni control system, and it has junction boxes on both sides to make the automation wiring straightforward. Compatibility with third-party automation is not stated on Hayward's product page, so ask before assuming it will join a non-Hayward system.
What does the warranty actually cover?
Hayward's 2026 Expert Line residential terms give 3 years parts and 1 year field labor on in-ground products, with 3 years field labor when the heater is sold by a Hayward Rewards dealer. There is no separate longer heat exchanger term. Heating elements and o-rings are treated as wear items, and the W3 version sold online carries 1 year parts only.
Do you install this heater in Sarasota?
Yes. We install and service Hayward gas heaters throughout Sarasota, Manatee, Charlotte & Pinellas County, Florida. This comparison page is written for pool owners anywhere; the installation offer is local.
Is the H400FDN right for your pool?
We install and service pool heating in Sarasota, Manatee, Charlotte & Pinellas County, Florida. If you are outside that area, the comparison above is still yours to use — ask your local contractor the same questions.
Licensed & insured · Florida Certified Pool/Spa Contractor #CPC1460367 · Mon-Sat, 8am-6pm
Last verified September 17, 2026
Specifications and warranty terms are taken from the manufacturer documents below. Manufacturers revise these without notice, so confirm the current terms before you buy. If you spot something out of date, email us and we will fix it.
Sources
- Hayward — H400FDN product page
- Hayward — Universal H-Series brochure (spec table, thermal efficiency, exchanger)
- Hayward — Universal H-Series Quick Reference Guide (flow, gas pressure, power selection, diagnostic codes)
- Hayward — 2026 Expert Line residential warranty terms
- Hayward — warranty resource page (Expert Line vs Open Line, Hayward Rewards)
- Hayward — Gas Heaters with OmniX (which SKUs carry OmniX)
Ratings on this site are the editorial opinion of Affordable Solar & Pool Heating, LLC, trading as Modern Pool Heating. How we rate heaters. Corrections: modernpoolheating@icloud.com.
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Mon-Sat, 8am-6pm · Licensed & insured · Florida Certified Pool/Spa Contractor CPC1460367