Hayward H500FDN Natural Gas Pool Heater Project – Installation & Review

In some areas of the country it’s probably more economical to select an electric heat pump or solar heater but for massive heating power you need a gas heater. We never seem to go halfway with anything and the pool heater was another case in point. Enter the Hayward H500FDN Half a million BTUs of Natural Gas heat. Did we even have to look at anything else?

Other advice upfront. If you are not “handy” …like 8 out of 10 handy or better, this is not a DIY project for you.

…Read the manual. Read the manual!

Skills you need to install this…Gas plumbing + PVC plumbing + Electrical

Please note that you will be working with gas (explosive), strong solvents (neurotoxic), and electricity (lethal voltages). If you are uncomfortable with any part of this project, you probably need to hire the respective trade to come do that part for you. Also call your local codes department and see if they need to do a permit / inspection. You should also call your gas company and find out if they need to be involved in any aspect.

I ordered this on the internet from https://www.poolsupply4less.com/

Amazon sells the H400FDN here (400k BTU).

The unit lists for $3058 and poolsupply4less has it for $2548 with free shipping. A handsome savings of at least $510. You are going to need that money for installation materials. I probably spent an additional $600 on top of the initial purchase in black iron pipe (gas line), fittings, PVC adapters, conduits, THHN wire, welding solvent, etc.

In just a few days the unit had made its way from California to my driveway.

The first thing you want to do before even singing the packing slip is to make 100% sure there is no visible damage to the unit. There is almost no chance of a refund or actions you can take if you sign the packing slip and later find damage.

Start by looking at the box exterior. There will be a “tip n tell” indicator. This is a special freight tool that will help you determine if the package stayed upright during it’s entire journey or if it fell off a forklift somewhere. If you have a lot of blue sand in the triangle portion, you might have problems.

Next (still before signing anything, with driver anxiously awaiting your signature and wanting to get back on the road) pull off the packaging material and expose the unit fully. If no dents or visible damage you are probably ok.

Note: The installation manual is inside the heater along with the cpvc couplings needed to connect into your plumbing and a few other extras like metal tie down straps if you live in an earthquake area like California.

“Tip and Tell” indicator on box.

This is no small heater weighing in at 197 lbs. uncrated.

Dragged into position with a rope tied to the pallet and attached to the lawnmower. Note the massive concrete pad. This was intentional forethought for the future heater. I’m really glad I have all this space.
Pay close attention to these minimums for future serviceability. I had some troubleshooting to do after installing due to a manufacturing defect. Was really glad to have the full 24” of clearance to open the unit up.
More considerations for “siting” the unit. It does vent some very warm air. Could possibly cause fires if not sited correctly.

Gas Plumbing

First things first, tap into the gas line.
A look at the gas pipe in the house shows 1 1/4” pipe is what we are working with.

I found it difficult to find this size pipe anywhere. Its beyond the size pipe most DYI’ers are using for anything except maybe to make table legs for Pinterest projects. Finally I found it at a Lowe’s. They cut and threaded all the sizes I needed. I think I only went back there about 3 times the same day. Not bad!

If you have never worked with gas pipe you will need a set of pipe wrenches. (Yes cheapskate, this means buy two of them).

Example of a pipe wrench. I’d recommend a 12” & 14” if you are only going to have 2 in your collection.

Plan out your pipe run. Also you need to account for your pipes screwing into the fittings as it will change your overall length.

The Lowe’s store I used cut the pipe to length and threaded it for me. In theory you are also supposed to de-burr the inside of the pipe to reduce gas turbulence and it can improve the gas flow and reduce the noise of the flowing gas. Given how loud the burner is for 500k BTUs it really seems like the noise generated by moving gas is unnoticed anyways.

Clean the threads with acetone or some nice solvent. I used the rest of my pvc cleaner. You ideally want to get the cutting oil off the threads. Two reasons for this.

1. You want your pipe thread sealer to stick to the threads. Use rector seal no. 5 https://rectorseal.com/product/rectorseal-no-5/ it is awesome stuff. The point is to lubricate the pipe so it will tighten tighter that you could tighten it without the lubricant. The threads on the pipe are tapered so the tighter you get them the more “sealed” the connection is. However you can go too far with that. Fittings can supposedly crack but I have never cracked one. I can see how a big boy could make it happen. With gas connections I personally prefer “tight” vs. “loose”.

2. Your heater will make everything smell like burning oil for the first month. (How do I know this?) clean everything extra good!

Using 1 1/4” pipe worked great as far as the final performance of the system. A pool contractor told me 90% of the time when DIY installed units fail to fire after install it’s because they don’t have adequate gas flow. This setup is about as free flow as you can get. I only stepped down the connection for the last few inches to adapt to 1” pipe for the gas solenoid fitting on the heater.

If you do several fittings you are going to be sore. It’s tough work. I’m pretty sure I got a few blisters.

Here is what the union on your gas meter looks like unhooked.
Another view unhooked. Make sure you shut off the valve before unhooking. Use 2 pipe wrenches to loosen the joint.
Tee added in to extend the line to the heater. I ran out of time and the kids still needed hot baths so I capped the Tee so we could turn the gas back on.

Note: I use rector seal no. 5 (yellow Teflon goo) for a thread lubricant to seal my gas pipes. Make sure your connections are very tight so no leaks!
Gas tee extension to new heater
Note: full flow 1 1/4” pipe / no restriction / reduction in sizing for optimum performance. Pipe primed to reduce corrosion.
Note: standoffs to mount the pipe per IRC code.

Water Plumbing

The unit comes equipped with a pressure relief valve if you sprung for the “ASME” model. (No one spends the extra cash in this configuration for residential use.) However, the heat exchanger on the standard model comes pre equipped with a 3/4” threaded hole for you to install your own. I found this to be an essential safety feature so I bought one. I’m sure in certain areas of the country it is required code. Below is the picture of the one I bought.

Safety pressure valve. Low price to pay for safety. Just use some rector seal no.5 on the threads and screw it in with the outlet facing the ground.

As far as connecting the PVC, I bought a ton of fittings. Elbows, half elbows, straight extenders, and a bunch of pipe. You can always return what you don’t need but it sucks to go to the store in the middle of a project!


Since all PVC pipe must be primed before gluing, the fastest way to accomplish this is to use a combination primer & glue. I prefer Oatey Clear Fusion.


It also looks great even if you are terrible with PVC because the primer is not colored.

Plumbing completed.


The Hayward system is not the only automation system you can use. In fact you can use the system standalone without a control via the onboard temperature control panel.

It sure is handy though to pick up my Hayward control and know what temperature the pool is and set it for whatever I want it to be.

Hayward integration makes controlling the temperature easy. This is a floating rechargeable remote!
Siemens GFCI’s are really important to use with pool equipment. They are the only breakers most pool electricians use as they are not prone to nuisance tripping.

For the power from your GFCI breaker source to the heater, use “liquid tight” flex conduit rated for outdoor use. Use the correct couplings to secure this conduit to both your power source and heater. You can use straight or angled couplings to make the installation cleaner depending on how you want to route your cable.

The wire for power and ground must be THHN cable, not NM cable like commonly found in houses. NM cable is not rated for use in conduits and will heat up. Check the install manual for sizing requirements. I used larger cable than necessary because I had some left over from wiring my hot tub. It was harder to work with but did the job and is theoretically ideal for having less resistance to current.

You will also need a separate conduit for your low voltage control cable unless you use an outdoor rated thermostat wire. Maybe overkill but I used both.

You will also need to run a bonding wire to the overall exposed earth ground your equipment is connected to.

This is why a large equipment pad is a necessity!

2 Comments on “Hayward H500FDN Natural Gas Pool Heater Project – Installation & Review

  1. WOW! Great job on the install and the technical explanation.
    Both are excellent work.


    • Still a work in progress. I have a pretty technical hands on background and it still was a real chore to install. Hopefully this helps anyone wanting to put a gas pool heater in. From what I have read so many people have problems with pool heaters and 99% of warranty issues not covered by manufacturers are due to incorrect installation. Thanks for taking the time to read.


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