Hayward H500FDN gas supply question

[spec2023]

Hello,
I'm wondering if anyone has a 500,000 BTU natural gas pool heater and how does your gas plumbing work?

My PB recommended to max out the BTUs on the gas heater to get things heated quicker, and we've ordered the 500,000 BTU model. The downside of this is of course the gas supply. Currently, I have a standard pressure (1/4 lb or 7 in w.c.) 1" gas line to the equipment pad, but the gas line is 150 ft, so according to the manual and gas line sizing tables, this is way undersized. The PB's response was a not very reassuring - "we'll connect it, see if it works, if it doesn't, you can dig up the gas pipe and replace it with a bigger one".

Now, I don't really want to dig up my backyard, nor do I want the extra expense of laying 150 ft of a huge 2" gas pipe. I've inquired with the gas company, and they can upgrade the pressure in my line to 2 lb. This will however require the use of gas pressure regulators for all appliances to get the pressure down to something usable. Currently, I only have 2 external tankless gas heaters, each at 180,000 BTUs. So I suppose each one can get the Maxitrol 325-BL-3/4 regulator: https://www.supplyhouse.com/Maxitrol-325-5BL-3-4-3-4-Line-Regulator-600000-BTU. The capacity is a bit too much, but this is the only one that matches the piping size that goes to the heaters.

For the 500,000 BTU pool heater, I'm now not sure which regulator should be used. The gas inlet piping to the heater is 1", so I suppose it's better to use a 1" regulator - the same model as above but at 1" https://www.supplyhouse.com/Maxitrol-325-5BL-1-1-Line-Regulator-600000-BTU, seems like a good bet. However, in the specifications it's saying that the maximum single appliance capacity is only 425,000 BTU, although for multiple appliances it's 600,000 BTU. So I'm wondering, if it would still be OK with a 500,000 BTU appliance? The pressure drop across the regulator would be a bit greater, but maybe should still be sufficient. The next size up is the 325-7 model, which handles 1,250,000 BTUs, but has a 1 1/4" pipe, so I think that would be oversized and incompatible with gas line and appliance sizing. The pipe would need to be stepped up and then stepped down, which may not be a good idea. Moreover, this model is much heavier, and more expensive.

So I'm wondering how are people are handling this discrepancy between regulator sizes and heater capacities? I wish I could consult with a "pro" locally, but so far all the plumbers that I've talked to are totally clueless about all this. They can certainly install what I'll ask them to, but it seems I need to design the system myself.

I'd appreciate any advice. Thank you.

 

[ajw22]

Change your order to a 400K BTU heater and it will simplify things.

For a 14K pool in Texas you don’t need a 500K heater.

 

[JoyfulNoise]

Also, for high pressure gas delivery, one usually has to use above ground galvanized steel pipe, not buried PVC. So even if you wanted to upgrade to a high pressure line, you need to check local code. Most local code will not allow high pressure NG lines to be buried nor use PVC.

Your PB clearly has no clue when it comes to gas lines. I highly suggest you get a qualified gas plumber to come out and give you options.

 

[ajw22]

1” pipe at 150 feet will not work with low pressure gas service for any size heater.

Who speced the 1” gas pipe @150’?

 

[ajw22]

The PB's response was a not very reassuring - "we'll connect it, see if it works, if it doesn't, you can dig up the gas pipe and replace it with a bigger one".

The heater may run with inadequate gas flow and run lean and not run at rated BTUs. If the heater ran you will get as much BTU heat as the gas can supply. Eventually the lean running heater will have problems.

Also the pool heater may die when other gas appliances try and fire up.

 

[spec2023]

@ajw22 @JoyfulNoise Thanks for the responses. I guess I need to try and find someone who knows what they are are doing. I'm beginning to regret the whole gas pool heater endeavor, because I underestimated the level of incompetence and/or ignorance on gas-related matters.

 

[JoyfulNoise]

The most critical aspect of a gas heater is sizing the supply line correctly. My gas run is 150ft from the meter to the equipment pad. When my PB spec’d the heater install for the plumber, we oversized the line and used 2” buried PVC. Have the conversation with the PB that you’re not comfortable with his recommendations and you want a qualified and licensed gas plumber to come and give options. Heck, if you have to pay the guy $100 to show up just for a chat, that’s well worth it compared to the overall cost of building a pool. Any qualified gas installer should be able to quickly read the spec sheet for the heater you intend to buy and then tell you exactly what needs to be done. It isn’t rocket science, you just have to avoid the “let’s just wing it” attitude of your builder.

 

[BMerrill]

For that size pool, a 250,000 heater will work just fine. If you use a solar cover, even better.
Contact gas company to make sure your service/meter will support the added demand of a gas heater.
With the current load you described you may already have a high pressure meter. Normal residential pressure is 1/2psi at the meter, high pressure is 2psi or greater. Service pressure to the meter is reduced by a service regulator before entering the meter. The meter outlet pressure is reduced at the appliances by their regulators to 7-11" WC depending upon the appliance.
From chart number 12 above, which is a 2 stage system, 3/4 pipe should work. The first stage is meter outlet pressure of 2psi or above to the heater regulator. The distance between the regulator and the heater (low pressure size) should be kept to less that 8'.
A licensed gas fitter should do all of the gas piping work. Its best, as mentioned above, to get him on board before ordering the heater.
American Meter-Gas Pressure Regulator: 1813C by Elster American Meter Co. will work just fine. I have this one.