By Hayward Pool Products



Part # W3H400FDP

Warranty 1 Year

Alternate Part #'s HAYW3H400FDP, HPPW3H400FDP

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:
Low NOx
Heater Type:

?     Asked on 4/28/2013by 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.

?     Asked on 4/1/2015by 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 4/21/2015by 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 5/21/2015by 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 2/25/2016by 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.


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 (Average 4.67  out of 5 stars)
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