Universal H-Series Low NOx Heater 400K BTU - LP - W3H400FDP



Part # W3H400FDP

By Hayward Pool Products

  4.67 Average  



Part # W3H400FDP

Warranty 1 Year

Product Description

Universal H-Series Low NOx Heaters
For In-Ground Pools and Spas - Electronic Ignition Dual Thermostat

Now With Cupro Nickel Heat Exchanger!

NEW Hayward Universal H-Series Low NOx heater combines industry-leading hydraulic performance; environmentally responsible low NOx emissions and a standard cupro nickel heat exchanger with a low profile appearance, lighter weight design, independent left or right side electric, water and gas connections plus 2" x 2 1/2" CPVC union connections to provide the ultimate installation flexibility for new or existing equipment pads.

It also includes a forced draft system that constantly moves air through the combustion chamber at a precise flow rate. As a result, all outside weather variables that can affect the heating performance, such as wind conditions, are eliminated - without having to install a high-wind stack.

NOTE: The Hayward Universal H-Series heaters meet the NOx Emission standards set by the California South Coast Quality Air Management Commission for 2001 and the Texas Natural Resource Conservation Commission Code.


  • Forced draft system constantly moves air through the combustion chamber at a precise flow rate, eliminating all outside weather variables that can effect the heating performance, such as high wind conditions -- without a high wind stack.
  • Our patented single header "V" baffle design heat exchangers allow for long life, fast heating and virtually no condensation. All Hayward heat exchangers are now constructed with highly resilient Cupro Nickel for greater durability and longevity even in salt-based, high flow or aggressive water chemistry set ups.
  • Easy-to-read L.E.D. digital Control Panel provides digital temperature readout and diagnostics for quick identification of components that might need service.
  • New polymer header provides superior hydraulic performance to save energy and protect against the damaging effects of erosion from high flow conditions for improved reliability.
  • Designed for today's larger diameter plumbing systems with 2" x 2 1/2" CPVC unions.
  • 1 Year limited warranty
  • Now with Cupro Nickel Heat Exchanger

Overall Dimensions

Product Specifications

400,000 BTU
197 lbs.
36-1/2 in.
0-10,000 ft.
Heat Exchanger:
Cupro Nickel
Special Feature:
Low NOx Emissions

?     Asked on 12/25/2020 by james kean

Heater tries to turn on but goes off within 3 or 4 seconds. What could be the problem. Thanks. Jim kean

A  Answered on 12/28/2020 by InyoPools Product Specialist Joe S.

Hello Jim, we would recommend you Contact Hayward Residential Product Support.

?     Asked on 4/27/2020 by kevin

Hello, Is the electrical 120 or 220

A  Answered on 11/4/2020 by InyoPools Product Specialist Hector F.

Hi Kevin, these units are set up as dual voltage so you can use either voltage and would just need to wire accordingly based on the installation manual. Please be advised that Hayward does recommend these be installed by a licensed qualified technician. 

?     Asked on 4/25/2020 by ted rodriguez

Is the electrical hookup 110 or 220 for the Hayward H series ?

A  Answered on 11/5/2020 by InyoPools Product Specialist Hector F.

Hi Ted, these Hayward Universal H-series heaters are dual voltage and can be wired for either 110/120 or 220/240 voltage per the installation details in the manual. Please be advised that it is also recommended that these be installed by a qualified licensed technician per Hayward warranty policy. 

?     Asked on 6/3/2019 by dana cook

I will need a COO with this purchase. Would you be able to get it? Thank you, Dana Cook

A  Answered on 6/9/2019 by InyoPools Product Specialist Lennox H.

Hi, Dana. We can look into getting you a Certificate of Origin (COO) for this item 

?     Asked on 2/9/2019 by Rich

How is the heater started. Does it need to be plugged in or does it have a gas grill type ignition starter? Thanks Rich

A  Answered on 2/11/2019 by InyoPools Product Specialist Lennox H.

Hi, Rich. This unit requires electricity in order for the unit to function. It does also have an electronic ignition system. 

?     Asked on 12/8/2018 by Steve

I have a large spa only that currently does not have a heater (old one has been removed.) I am looking at this or the Hayward 500K BTU unit. Can you confirm the efficiency of this over the 500? Is the 500 worth the extra money?

A  Answered on 12/10/2018 by InyoPools Product Specialist Steve M.

Good Afternoon- Normally, the higher the BTU the more efficient the heater. The efficiency comes from the length of time it would take to heat your pool. The higher the BTU, the faster your water will be heated. The faster your water heats up the less time your heater has to run and less power or gas that it has to use. Between the Hayward Universal H-Series Low NOx Heater 400K BTU - LP - H400FDP and the Hayward Universal H-Series Low NOx Heater 500K BTU - LP - H500FDP, you won't see much difference in efficiency.

?     Asked on 11/25/2018 by Chris

Can you confirm this heater is shipped set up for LP (propane) gas, and does not need a separate conversion kit?

A  Answered on 11/26/2018 by InyoPools Product Specialist Hector F.

Yes, these heaters do come set up for propane usage. 

?     Asked on 6/23/2018 by WILLIAM MASON

im looking for a heater or chiller i live in oklahoma trying to figure out if i need both or just heater.my pool is 43 x 16 lazy l with steps. 8ft to 4ft could you advise on the best one im totaly electric but thinking i would install a propane tank if needed

A  Answered on 6/30/2018 by InyoPools Product Specialist Lennox H.

Hi, William. You can use a Heat/Cool Heat Pump which will heat your pool in the spring and fall then cool in the summer. You may need to supplement the heat pump with a gas heater depending on how fast you want the pool heater. 

?     Asked on 5/13/2018 by Darrin

I recently purchased a Hayward heater, 400k BTU. All my pool plumbing is 1 1/2" PVC the inlet and outlet on the Hayward is 2" - Is it okay to use a 2" to 1 1/2" reducer in order to connect this to my existing plumbing? thank you

A  Answered on 5/13/2018 by InyoPools Product Specialist Hector F.

Yes, that is a common adjustment that is made on some pool systems. 

?     Asked on 11/8/2017 by Mike

I am looking to replace a Hayward H400IDL2 with an H400FDP unit. Are the water inlet/outlet locations the same on both units or will I have to do some plumbing to install? One recommendation I received while researching a replacement was going with the same manufacturer, the alignment should be the same.

A  Answered on 11/8/2017 by InyoPools Product Specialist Lennox H.

Hi, Mike. Unfortunately, replace the H400IDL2 unit with the H400FDP will not be a drop-in swap. You will have to redo the plumbing. The water connection height on the H400FDP is 1/2" higher than the H400IDL2 unit.

?     Asked on 6/19/2017 by Dave

Hello, I currently have a Jandy LX 399,000 BTU heater (approx 10 years old). The replacement part I need for it is no longer available so I need to buy a new heater. I am looking at the Hayward H400FDP as a replacement for it. My existing unit has 2" inlet and outlet ports, but I see that the Hayward unit has (1) 2" connection and (1) 2 1/2" connection. Will it be ok for me to install this unit with a 2" x 2 1/2" reducer to my existing piping? Thank you

A  Answered on 6/19/2017 by InyoPools Product Specialist Patrick P.

Hi Dave, yes it will be fine to install the Hayward heater as you described and the H400FDP would be a great replacement for the Jandy LX heater.

?     Asked on 6/19/2017 by

can heat exchanger be reversible to left hand side hook up

A  Answered on 6/19/2017 by InyoPools Product Specialist Lennox H.

Hi. The water connection can be reversed by an authorized technician.

?     Asked on 6/2/2017 by BobNJ

Is there an efficiency rating on this heater? Does it vary much among major brands?

A  Answered on 6/3/2017 by InyoPools Product Specialist Patrick P.

Hi Bob, This heater is rated at 84% Efficient which is one of the higher ratings. There really is not much of a difference between the major brands as they range from 82% - 84% Efficient.

?     Asked on 3/1/2017 by

Can this heater be installed inside a equipment house if ventilated?

A  Answered on 3/1/2017 by InyoPools Product Specialist Lennox H.

Hi, This heater can be installed indoor with the proper ventilation kit. The ventilation kits are listed on the Hayward Heaters page.

?     Asked on 9/3/2016 by guest

i'm trying to change the heater controller on the faceplate of the heater , but i can't find the part number.

A  Answered on 9/14/2016 by InyoPools Product Specialist Lennox H.

Hi, You can locate the controller and all available replacement part for this unit via the Hayward Universal H Series Low Nox Heaters Parts page.

?     Asked on 6/2/2016 by louie

hi... i have the hayward h400 ( millivolt ?) propane heater. its more square than the one in this picture. the heater element needs replacing and its very expensive( $1000 bucks plus installation). i thought it more wise to replace the heater since it is already 14 years old. which do you recommend. pool is in ground 45X25. thanks

A  Answered on 6/3/2016 by InyoPools Product Specialist Scott W.

Hi Louie,If you're wanting another Hayward propane heater the part number H400FDP would be the one you'd want to go with. If you're looking for a recommendation, I would recommend the RayPak 406,000 BTU which is part number PR406AEP.

?     Asked on 2/25/2016 by shawn

Hello, We need to replace our Hayward H400 with a new unit. Will this unit work perfectly with the Goldline/Hayward pool automation system, mainly being able to control from the Aquapod? Thanks

A  Answered on 2/25/2016 by InyoPools Product Specialist Joe S.

Hello Shawn, if you have full Hayward automation it will pair up with this Hayward heater where you can control the temperature and switch between pool and spa modes.

?     Asked on 5/21/2015 by chris

how do i know what size (btu's) heater I need for my pool ?

A  Answered on 5/22/2015 by InyoPools Product Specialist Patrick P.

Hi Chris we address this question about 1/2 down this page How Do I Size a Heater For my Pool. If you have any addtional questions after looking at that page then let us know, but I think this page should help out quite a bit.

?     Asked on 4/21/2015 by George

I want to install the Hayward Lownox heater on my pool but I live in the mountains at 3,000 foot elevation; do I need to buy a special high elevation heater?

A  Answered on 4/21/2015 by InyoPools Product Specialist Matt S.

Hello George, The Hayward Universal Low Nox are self adjusting up to 10,000 feet of elevation. Any installation above 2,000 feet will require a special restriction plate to be installed. Luckily, that plate comes standard with every heater so no need to purchase it separately.

?     Asked on 4/1/2015 by Rich

Is there a difference between "H series" and "Universal H series" if so what is it?

A  Answered on 4/2/2015 by InyoPools Product Specialist Andy O.

Rich- the H series is the older model to the Universal H series. The H-series is now only available in smaller millivolt and above ground models. The H-series inground models come with a cupro-nickel heat exchanger and the above ground comes with a standard one piece copper exchanger. Whereas the Universal H-series all come standard Digital with a curpo-nickel heat exchanger as well as Low NOx.

?     Asked on 4/28/2013 by Guest

How can I tell the difference between a Propane or Natural Gas heater listed on your website?

A  Answered on 4/28/2013 by InyoPools Product Specialist Patrick P.

A heater's model number will usually end with an 'N' or a ''P' to denote the gas type. if the model number is only numbers we also have the gas type in the description of the product. The abbreviations "NG" is for natural Gas and "LP" is form Liquid Petroleum, also called Propane.


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