Part # W3H400FDN
Warranty 1-Year Parts-Only Warranty
Hayward® W3H400FDN Universal H-Series Low NOx Pool & Spa Heater – 400,000 BTU, Natural Gas
Powerful Heating. Built for Salt Pools. Flexible Installation.
The Hayward® W3H400FDN is a 400,000 BTU natural gas heater designed for large residential in-ground pools and spas. Engineered for ultimate performance, energy efficiency, and corrosion resistance, this model features a Cupro Nickel heat exchanger that stands up to salt-based and aggressive water chemistry.
Its Low NOx emissions meet the toughest air quality standards, making it the perfect choice for California, Texas, and other regulated regions.
Key Features:
400,000 BTU/hr Heating Power – Ideal for larger pools and rapid heat-up times
Natural Gas – Electronic ignition with dependable performance
Cupro Nickel Heat Exchanger – Superior corrosion resistance and long-term durability
Low NOx Certified – Meets California South Coast AQMD & Texas Natural Resource Commission codes
Forced Draft Combustion – Consistent heating unaffected by weather or wind
LED Digital Control Panel – Easy diagnostics and precise temperature settings
Right/Left-Side Connections – Maximum plumbing and gas line flexibility
2" x 2.5" CPVC Union Connections – Compatible with modern high-flow plumbing systems
Polymer Header Design – Reduces erosion from high flow rates
Specifications:
Model: W3H400FDN
Fuel Type: Natural Gas
BTU Input: 400,000
Ignition Type: Electronic
Union Connections: 2" x 2.5" CPVC
Dimensions: 32.6" L x 30.6" W x 24.0" H
Weight: Approx. 160 lbs
Warranty: 1-Year Parts-Only (Limited)
Applications:
In-ground residential pools and spas
Saltwater systems
Pools requiring fast recovery and high BTU capacity
Environments requiring low-emission equipment
✅ Why Choose the Hayward W3H400FDN?
Highest BTU option in the H-Series lineup
Perfect for quick heating of large pools or high-demand spas
Engineered for long-term durability and flexible installs
Trusted performance from one of the most recognized pool equipment brands
Overall Dimensions
How do you know if a pool heater is a propane heater or a natural gas heater?
Reply
Typically in the product name we use the abbreviation of "LP" for propane or "NG" for natural gas. Click here for a full listing of our >Pool Heaters.
Reply
Will a gas heater operate at the low speed of a dual speed motor?
Reply
Probably not - Most gas heater will shut off at low GPM levels (20-40) to keep the heater cores from overheating - 20 for 200 BTUs, 40 for 400 BTUs. Depending on your pool system you might get these GPM levels at the low speed but generally these heaters must be run at the motor's high speed.
Reply
What is the difference between an Electronic and Millivolt ignition?
Reply
The basic answer is that Millivolt is the old style of ignition, using a standing pilot light. While the electronic ignition uses a spark start system like a gas grill. Electronic ignitions are more efficient in gas usage and also are better suited for high wind areas where a pilot light might get extinguished.
Reply
Is a vent required for typical outside installation for the Hayward 150k Ng Lo Nox heater?
Reply
For the Hayward Lo Nox heater, you would not need to purchase an additional vent if you are using it outside. If you are installing the heater outside, we recommend you purchasing a heater cover. This will protect your heater from debris, rain, snow, heat- or pretty much anything that could get caught in your heater. The Weather-Out Pool Heater Cover can be viewed on our website.
Reply
2 to 4 hrs
Screwdriver, Pliers, Wrench Set, Adjustable Wrench, Multimeter
2 0
Asked INYOPOOLS.COM forum which heaters were recommended. Got a reply almost immediately and proceeded to look through internet for best price on that brand/model. INYOPOOLS.COM not only had an extremely competive price but also provided the knowledge on which product would work best for my needs and info on how to install it.
Got heater from delivery service - they placed right in front of garage. Heater was heavy but not too much for two adults to move into place. Old heater was already removed from exisiting pad. Connected gas line with minimal adjustments to old setup. Replumed pool PVC lines as it was slightly different setup than old Jandy heater. Tested elecrircal volts to confirm it was 240v. Connected electric and tested heater - it kicked right on after about 30 seconds.
Was in hot tub that night enjoying!
Less than 1 hr
Screwdriver, Adjustable Wrench
1 0
I had this heater installed by a plumber and electrician in about 30 minutes! It is so quiet that the only noise is from the flames on the burner, and it heats my pool water at about 2 - 3 degrees per hour. Plus, because I live in the Northeast I have to winterize my filter, etc. This heater is very easy to winterize as the instructions are precise and very easy to follow. A perfect pool heater!
The Most Helpful Review
20 0
(5 out of 5 stars) Awesome Heater
Reviewed By: Tiffany4004 from Jackson, NJ ()
Pros: Price, Works Quickly, Effective
Cons: nothing
This heater is awesome..It works so quickly and it is very easy to use..It was also cheaper on inyopools.com then other websites.. I love it !
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The Most Recent Reviews
(5 out of 5 stars) Good product
Reviewed By: Inyo Customer ()
Good product
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1 1
(5 out of 5 stars) Hot tub back in action!
Reviewed By: Inyo Customer ()
What a great product - easy to install, quality build and works great!
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2 0
(5 out of 5 stars)
Reviewed By: Inyo Customer ()
Heater arrived within 3 days of ordering it online...perfect condition. Installation took all of 30 minutes by plumber and electrician. Runs extremely quietly...very efficient, and heats my water 2 - 3 degrees per hour. Perfect! A must buy!
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1 0
(5 out of 5 stars)
Reviewed By: Inyo Customer ()
Heater is fantastic came to my door 3 days after order was packaged extremely well so no damage looks n runs great was up n running few days after receiving it lol had to wait for electrician pool was at 79 degrees turned heater on and had it up to 88 degrees in 4 hours for a pool 18x38 inground absolutely thrilled and price was 1000$ less than my pool company and a few hundred less than other website with free shipping so was a no brained there ty inyopools
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1 0
(5 out of 5 stars)
Reviewed By: Samuel I. from New York ()
Pros: works good
Cons: very big unit
its a real big unit. i was amazed to wee how big it was. works good
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(5 out of 5 stars) hayward 400k heater
Reviewed By: John R. from merrick, NY ()
Pros: works great, and great price at inyo
Cons: none
compact, powerfull, e z to install (replaced my EXPENSIVE heat pump with it, and what a wasye of money that thing was)
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1 0
(5 out of 5 stars) great pool heater
Reviewed By: John R. from merrick, NY ()
Pros: price of unit, very good warm up rate, considering my pool is 50,000 gallons
Cons: NONE
great heater, fantastic price..inyo beat evry one by at least $200 or more, came in 4 days delivery was a breeze, looks good e z to install (put it in in place of my heat pump, WHICH WAS A WASTE OF TIME AND MONEY, REALLY BIG WASTE)
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