Hayward Pool Heater for Inground Pools Universal H-Series 400,000 BTU (Natural Gas Pool Heater) Pool and Spa Heater W3H400FDN Replacement for H400FDN
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Availability:
Only 4 left in stock, order soon!
Arrives
Jul 11 – Jul 12
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Size: 400,000 BTU (W3H400FDN)
Features
- EASY TO USE: Intuitive inground pool heater control panel enables easy operation and maintenance. The digital LED display helps maintain pool water temperature while monitoring pool water heater performance with self-diagnostic capabilities
- MULTIPLE COVERAGE OPTIONS FOR POOLS AND SPAS: This gas pool heater and pool and spa heater suits in-ground pools and spas up to 1200 sq ft with a natural gas connection; additional models cover 450, 600, or 750 sq ft
- ENERGY SAVING AND BUILT TO LAST: Efficiently designed pool heater for inground pools helps deliver consistent hot water for swimming pools, reduce pump run time for energy savings, and protect against corrosion caused by unbalanced water chemistry
- SIMPLE INSTALLATION: This 400,000 BTU Hayward natural gas pool heater allows flexible gas and electric connections on the right or left side, with an H-Series built-in 3/4" gas connection for easier fuel line setup
- LOW ENVIRONMENTAL IMPACT: Hayward gas pool heaters for inground use are certified for low-NOx emissions and eco-friendly operation, reducing circulation pump run time while delivering a reliable swimming pool heater solution for inground pools
Description
The Universal H-Series 400,000 BTU Natural Gas Pool & Spa Heater from Hayward provides reliable, long-lasting comfort for pools and spas with a surface area up to 1,200 ft. Built with a durable cupro nickel heat exchanger, it offers exceptional protection against corrosion and premature failure caused by unbalanced water chemistry, ensuring you get season after season of premium heating performance. The Universal H-Series boasts industry-leading hydraulic performance coupled with lightning-fast speed-to-heat capability—so you spend less time waiting, and more time swimming. Its low NOx emissions meet air quality standards in all low-NOx areas, so you can rest easy knowing its environmental impact is low, too.
Product Dimensions: 29.5 x 34 x 24 inches
Item Weight: 195 pounds
Manufacturer: Hayward
Item model number: W3H400FDN
Frequently asked questions
If you place your order now, the estimated arrival date for this product is:
Jul 11 – Jul 12
This item is non-returnable:
Non-returnable. Transportation of this item is subject to hazardous materials regulation
View our full returns policy here.
Non-returnable. Transportation of this item is subject to hazardous materials regulation
View our full returns policy here.
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Similar Products
Top Amazon Reviews
Size: 400,000 BTU (W3H400FDN)
Easy to install. Not cheap, but efficient heater for my large pool. It has been 2yrs, and aside from the mice that ate the wiring harness to the display, it was worked great (display was easy to replace and parts are easily accessible which is also nice to make sure this lasts for a long time to come. I think the wires may have been soy based insulation which may be part of the problem). Otherwise it fit where my prior unit was as I just replaced the 20+ year old unit. Not the quietest of devices, but as this is my first pool/hot tub...not sure if they get quieter.
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Reviewed in the United States on September 5, 2025 by Rob
Size: 400,000 BTU (W3H400FDN)
So I purchased nearly identical model 17 years ago. Self installed except for need of larger supply line for gas input that required a licensed plumber. While I did have a couple failures related to the odd geckos crawling up behind a circuit board with 220 voltage (part easily obtained from Amazon and replaced myself) and shorting out. The heater performed wonderfully! Fast forward to this spring and it was not working after winter months. No input from control board. Tested things I was sure of to no avail. BUT then realized this was 17 years old! I purchased this newer version and it arrived. Unwired and unplumbed from old and connections identical to new. Rewired and replumbed in about 45 minutes and it was up and running 100%. Highly Recommend Hayward products. I also use there pool pumps and sand filters among other odds and ends. Always satisfied!
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Reviewed in the United States on September 1, 2023 by Douglas Pilcher
Size: 400,000 BTU (W3H400FDN)
Have had this heater for three seasons. Only need to use it for a few weeks per year at the beginning and end of summer. It hasn’t run constantly during that time but mostly when the kids wanted to swim and water was cool. Went to start up go this season and unit will not work. Dan comes on but nothing else. Had a pool company come check it out then they called Hayward for parts and was told that the unit was discontinued and there’s no parts available. I was shocked and find this completely unacceptable especially considering the cost, time from date of purchase and that this is supposed to be a reputable company. I would absolutely consider another brand.
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Reviewed in the United States on May 24, 2026 by Chris
Size: 400,000 BTU (W3H400FDN)
Heater works great had a 200,000 Hayward prior to this and a 20,000 gallon inground pool the 200,000 struggled to keep up and eventually stopped working so I decided to go big with the 400 great move because it pretty much slipped right into the same fittings that the 200 had the only thing I had to change was my gas and that was minimal Had it up and running in a couple hours and heated the pool 20° overnight. The shipping was excellent R & L carriers delivered it. It showed up without a mark on it. It was a few days late, so I was mad about that but other than being a few days late I definitely go back to that company again they did a great job shipping it
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Reviewed in the United States on August 20, 2023 by jim
Size: 400,000 BTU (W3H400FDN)
Driver drop off heater without ringing doorbell wonder why? Cosmetics damage- How would feel receiving a new car with a dent on the fender? Hopefully the heater operation will work. I am waiting for the installer.
Reviewed in the United States on July 10, 2022 Reviewed in the United States on July 10, 2022 by Reggie Wynn
Size: 400,000 BTU (W3H400FDN)
So glad I tripped the trigger on this. I went with 'go big, or go home'. I'm only heating a 15,000, but when I want to heat it up for visitors, we live in S. FL we get many, I don't want to have to start days before like I did with a heat pump. And if the weather was cooler, yes it does happen in S. FL, it would take a heat pump forever bypassing the timer and running it 24/7. This brings the pool up three degrees an hour. And with a lightweight cover this can't be beat. And when the visitors want to use the spa it's up to temp in minutes, not hours. If you're just not sure about gas vs. heat pump, take my word for it, this is where you want to be. You don't need to run it as long to get to, and maintain where, you want to be. You could run this thing in the dead of winter no matter where you are. Good luck trying that with a heat pump.
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Reviewed in the United States on December 10, 2021 by K
Size: 400,000 BTU (W3H400FDN)
Bought this to replace an old broken rusted out Hayward H400IDL that was about 15 years old. My old heater seemed to breakdown every 3 months or so. I’m hoping this one will be more reliable. The installation wasn’t to bad I did it myself but the biggest negative was when I called Hayward and they told me the H400FDN was an exact replacement that wouldn’t need plumbing adjustments to fit but that wasn’t the case both the water and gas connections had to be reworked to line up. Nothing to difficult but it required a trip to Lowe’s to get everything working. Overall it seems like a good heater although it doesn’t look like the picture shown on amazon? the control panel is completely different then what is shown. Also don’t forget to register online for your warranty and apply for a rebate with your local gas company I got an extra $300 off with a rebate from SoCalGas.
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Reviewed in the United States on July 24, 2020 Reviewed in the United States on July 24, 2020 by Matthew
Size: 400,000 BTU (W3H400FDN)
I had this heater installed and week ago and it has never worked. The ignite never worked. I have called Hayward they said it’s possibly the flame detector part. The warranty covers the part but not the labor. If we had bought it through a local dealer they would have had a better warranty and covered labor because they would have installed it. This seller definitely didn’t give support. Pretty much said to contact Hayward and if I wanted to return it I would need to pack it up, drill it down to the wood crate, just like I got it and pay for shipping. If I had it to do over again I would not order it online and have it installed by another professional. I wish I would have known this before I ordered it.
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Reviewed in the United States on June 26, 2026 by Shari