Hayward Universal H-Series

The Universal H-Series is Hayward's gas heater, and it runs from H150FD to H500FD — seven sizes against the five Pentair offers on the MasterTemp. N on the end is natural gas, P is propane.

Hayward lists the plain H400FDN as discontinued, replaced by HS400FDN, the Universal H-Series with OmniX. It isn't simply this heater with an app added. Its brochure gives narrower cabinets (34 inches against 36 on the 400), 84% rather than 83% on the 250, and sizes of 135 to 500 with no 300 or 350, and its manual asks for different clearances. The H-Series is on an enormous number of pads and every part below still fits it, which is why this page exists.

Cupro-nickel in every model, and it costs nothing

This is the real difference between the two big gas heaters, and it runs the opposite way to what you would guess from price.

Hayward's brochure heads its own specification table with "exclusive high-performance cupro nickel heat exchanger in all models", and the table lists Cupro Nickel against every size. Efficiency is 84% on the H400FD, 83% on the 250 and 200, and 82.7% on the 150.

Pentair's MasterTemp ships a copper exchanger at 84% and sells cupro-nickel as a heavy-duty option at 82% — you pay more and give up two points of efficiency for the corrosion resistance.

Hayward includes it, at its best efficiency. On a salt pool, on well water, or anywhere the water runs aggressive, that is a genuine advantage and it does not show up on a price comparison. Whether it matters to you depends on your water, and the LSI calculator will tell you whether yours is the aggressive kind.

Note the efficiency rises with size rather than being one number for the line. The 400 is the most efficient model Hayward makes here, which is unusual and worth knowing when comparing a small H-Series against a small competitor.

The flow range, and the sentence attached to it

Every model has a minimum, and Hayward's wording about missing it is harder than most manufacturers use.

• H150FD, H200FD — 20 GPM
• H250FD, H300FD — 25 GPM
• H350FD, H400FD — 30 GPM
• H500FD — 40 GPM

The ceiling is 125 GPM on every one. Above that Hayward requires a manual bypass valve, set with a flow meter on the outlet and the handle removed afterward so nobody moves it.

Then the warning: "Damage caused by flow rates outside this range will void the manufacturer's warranty", and on the bypass, "The heat exchanger will fail and this damage will not be covered under the Hayward warranty."

Two things follow. First, this is another place where running a variable-speed pump slowly to save money collides with equipment that needs flow — set a heating speed rather than one speed for everything. Second, Hayward asks for the minimum to be calculated or measured with the in-floor cleaning system running, and with any other jets or water features on. The worst case is what has to clear the minimum, not the quiet case.

Worth noting against the Pentair figures: a MasterTemp 400 needs 40 GPM where an H400FD needs 30. If your plumbing is marginal, that difference is a real reason to prefer one over the other.

Forced draft, and what it buys

The H-Series is forced draft — a blower moves air through the combustion chamber at a set rate rather than relying on natural convection up a stack.

The practical consequence is that it needs no high-wind stack, which is why an H-Series looks like a low box rather than something with a chimney on top, and why it is easier to fit under a low overhang. It also means the blower is part of the ignition sequence: it has to run and prove itself on the vacuum switch before the gas valve opens. A heater that hums and never lights is often the blower or that switch, not the igniter.

Outdoor clearances are asymmetric and worth measuring before the pad is poured: top unobstructed, front 24 inches, back 6, water connection side 12, and 6 on the far side. The front figure is the one that catches people, because 24 inches is more than a heater looks like it needs.

Ordering parts for one

Most electrical parts are one number across the whole line — igniter, flame sensor, control board, transformer, water pressure switch, high limit. That makes the common repairs easy to order.

What varies by size: heat exchanger, gas manifold, burner orifice kit, heat barrier panel, blower inlet baffle and rain guard. And the H500FD is the exception to the exceptions — it takes its own blower, its own gas valve and its own orifice kits where every other size shares.

The ASME versions have their own exchanger numbers again, with an A suffix, and they ship with a drain valve and pressure relief valve that non-ASME heaters do not have. On a non-ASME heater the header carries a ¾ inch port with a brass plug in it; if local code wants a relief valve, that is where it goes.

Converting between fuels

Hayward sells quick-change conversion kits in both directions for every size — FDXLGCK1400NP takes an H400FD from natural gas to propane, FDXLGCK1400PN brings it back.

That is a genuine convenience compared with heaters that need the whole manifold changed, but it is still a gas job. Converting a heater changes its orifice and its regulator setting, and getting it wrong produces a yellow flame, a lifting flame, or a heat exchanger that soots up — the three symptoms Hayward names for incorrect gas pressure.