Hayward vs Raypak/Rheem Natural Gas Pressure Requirements

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rscam

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Hi. I'm trying to select a heater to replace an existing Hayward H-350 natural gas heater. I was leaning toward Raypak/Rheem based on all the great reviews here but when I started reviewing the installation manuals I noticed that the Rheem says it requires 6" W.C. upstream of the regulator with the regulator set to 4" W.C. Meanwhile the direct Hayward 350 replacement calls for 4.5" W.C. upstream with a manifold pressure of 1.8 to 2.0" W.C. Unfortunately I don't know what pressure the existing heater was getting when it was operational. It worked fine for a year after we bought the house and then died (was 20 years old)

Does it seem reasonable that the 2 designs would have such different pressure requirements or could this be a case of Raypak overstating their needs as a cya?

Assuming there is something inherent in the design of the Raypak that requires higher gas pressure, I'm leaning Hayward for peace of mind that it'll work. My best guess is that I have about 100 to 120 ft equivalent pipe length with 1 1/4" steel pipe which is tight to begin with. I have a comfort level that the old Hayward worked fine (it even actually apparently needed a little more at the manifold 3.5" vs the new Hayward which seems to need only 2.0).

I'm just looking for a sanity check on my thoughts above and any insight into the differences between the gas pressures required for the Hayward vs Raypak/Rheem natural gas heaters. As well as any other models I should be considering (Pentair? Jandy?). I am also trying to avoid overthinking it. It might be that if it worked for the old Hayward, it'll work for the Raypak and I end up with a heater that's not as reliable just because the manufacturer was less conservative in stating it's pressure requirements.

Any help would be greatly appreciated.

Ron

PS I attached a couple screenshots from the install manuals
 

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Hayward/Pentair/Jandy heaters used a forced draft design that uses a blower fan to create air flow.

Raypak heaters used a natural draft design with air coming in the bottom and naturally flowing out of the top.

Two very different designs with different air/gas mixture requirements. There are pros and cons to each design.

Forced draft heaters have a smaller form factor and are more compact. The burners are sealed in a can and less likely to corrode. Forced draft heaters have an air blower and complex controls.

The Raypak heater is a larger natural draft heater that has simple operation but since it’s burners are open at the bottom it tends to develop corrosion around the burners.

Raypak now has the Avia model heater that is a forced draft design.

Your house gas service should be able to run either heater design if your gas meter has sufficient capacity.
 
Last edited:
ajw22 said:
Hayward/Pentair/Jandy heaters used a forced draft design that uses a blower fan to create air flow.

Raypak heaters used a natural draft design with air coming in the bottom and naturally flowing out of the top.

Two very different designs with different air/gas mixture requirements. There are pros and cons to each design.

Forced draft heaters have a smaller form factor and are more compact. The burners are sealed in a can and less likely to corrode. Forced draft heaters have an air blower and complex controls.

The Raypak heater is a larger natural draft heater that has simple operation but since it’s burners are open at the bottom it tends to develop corrosion around the burners.

Raypak now has the Avia model heater that is a forced draft design.

Your house gas service should be able to run either heater design if your gas meter has suf
Click to expand...
Thanks Allen. Im pretty sure the old Hayward was natural draft. I assumed new one would be same, I'll look at that.

Regarding the gas service, what started me down this rabbit hole was looking at my gas utility guidelines. My regulator is supposed to supply 5 to 7 inch WC pressure. But the gas utility (National Grid) handbook says pressure can be as low as 4" at wall and appliances should be sized to need no more than 3.5 manifold pressure at burner. Raypak needing 4 at manifold and 6 upstream got me worried.
 
What is wrong with your current heater?

A gas tech can put a manometer on the gas valve of your current heater even if it does not light. And he can jumper 24V onto the gas valve to open it and measure gas pressure with it open.

Post pics of your current heater. I was describing current models design.

@swamprat69 may have ideas about gas pressure requirements.
 
I don't see any reason why a replacement wouldn't work unless it's btu rating is vastly different.

For example, I replaced a jandy lars lite 250k btu heater with a raypak 266k btu heater and it works just fine....if I wanted a 400k btu heater, then that might not work and need a different regulator.
 
ajw22 said:
What is wrong with your current heater?

A gas tech can put a manometer on the gas valve of your current heater even if it does not light. And he can jumper 24V onto the gas valve to open it and measure gas pressure with it open.

Post pics of your current heater. I was describing current models design.

@swamprat69 may have ideas about gas pressure requirements.
Click to expand...
I posted pics of old heater. Water side corroded to point where header leaked. I cut heater out of the piping and abandoned in place. Didn't realize that you could get a full picture of the gas supply available without it being fully operational. I'm handy but not much experience with troubleshootinh available gas flow/pressure issues.
 
swamprat69 said:
If there is a regulator installed by your gas meter then the nominal supply pressure would be 6" WC + or - 1"WC meaning the lowest supply pressure would be 5"WC
Click to expand...
Yes. I have a regulator upstream of my meter. So I should be getting between 5 and 7 on the load side. (Even though gas company doesn't seem to guarantee more than 4 at my "wall")

What I'm pondering is that since Hayward specs call for 4.5 at the heater regulator with 2.0 after while Raypak seems to want significantly higher (6 with 4.0 after) that Hayward may be safer bet.
 
As long as there is no significant pressure drop due to inadequate pipe sizing, either choice should be OK. I am running a 17 yr old Hayward heater ( have had it for 11 years ) that has had no problems other than replacing the hot surface ignitor and water header gasket and display (fading and loss of mode LEDs)
 

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swamprat69 said:
As long as there is no significant pressure drop due to inadequate pipe sizing, either choice should be OK. I am running a 17 yr old Hayward heater ( have had it for 11 years ) that has had no problems other than replacing the hot surface ignitor and water header gasket and display (fading and loss of mode LEDs)
Click to expand...
Thank you. I'm going to try to check the pressures that I currently have at the heater as Allen suggested to gain a comfort level that it's adequate and I'll take it from there. You all have been very helpful.
 
rscam said:
Rheem says it requires 6" W.C. upstream of the regulator with the regulator set to 4" W.C.
Click to expand...
It says 6 to 10.5" w.c.

1678629365837.png
rscam said:
Meanwhile the direct Hayward 350 replacement calls for 4.5" W.C. upstream with a manifold pressure of 1.8 to 2.0" W.C.
Click to expand...
It says 4.5 to 10.5" w.c.

screenshot_20230310-142129-png.476631


It's basically the same thing.

The meter will put out either low pressure (about 7.0" to 13.8538" w.c (0.5 psi)) or high pressure (about 2 psi).

If the meter puts out 2 psi, then you use a regulator near the appliance to drop the pressure to about 7.5" w.c.

The meter is not going to put out 4" w.c.

Normal output is about 1/4 psi to 1/2 psi.

0.25 psi is 6.9269" w.c.

If the pressure is lower than 7", then it is too low and it should be increased.

As long as the line is sized correctly, the pressure will be fine.

You will have a static pressure and a dynamic pressure.

Static is when the heater is off and dynamic is when the heater is running.

The dynamic should not be more than about 0.5" w.c lower than the static.

The dynamic should not be lower than the minimum.

Don't worry about the manifold pressure.

As long as the supply inlet dynamic pressure is above the minimum, the manifold should be fine.

Can you show your meter data plate?

What is your current pressure?
1678629700208.png
1678629732960.png
 
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rscam said:
My best guess is that I have about 100 to 120 ft equivalent pipe length with 1 1/4" steel pipe which is tight to begin with.
Click to expand...
At 100 feet, a 1.25" line is ok.

If it is over 100 feet, then you have an undersized line for any heater over 250,000 btu/hr.

You need to check the static and dynamic pressure to make sure that you don't have a big pressure drop during operation.
 
You should have a regulator near your meter that looks like this.

The pressure output range should be stamped or on a data label.

Normal is about 5.5" to 14" w.c.

This shows 5.5" to 8.5" w.c.

The pressure can be adjusted to 8.5" if necessary.

gas regulator.jpg

1678631623942.png
 
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Natural gas piping systems in residential single-family and multi-family buildings typically operate at standard delivery pressure, 1/3 pound-per-square inch gauge.

1678634496243.png

Residential New Construction 2 PSIG Program | SoCalGas

Residential New Construction 2 PSIG Program means lower costs. Learn how utilizing elevated pressure can save you money in new residential building projects.
www.socalgas.com www.socalgas.com

1/3 psi = 9.23577" w.c.
 
JamesW said:
Natural gas piping systems in residential single-family and multi-family buildings typically operate at standard delivery pressure, 1/3 pound-per-square inch gauge.

View attachment 476852

Residential New Construction 2 PSIG Program | SoCalGas

Residential New Construction 2 PSIG Program means lower costs. Learn how utilizing elevated pressure can save you money in new residential building projects.
www.socalgas.com www.socalgas.com

1/3 psi = 9.23577" w.c.
Click to expand...
James
Thank you for your help. I do have a pressure regulator which according to the nameplate should be supplying 5 to 7 inch. See pic.

I realize now that the stuff I saw in the guidelines from my utility company (where it mentioned pressures as low as 4" at my wall) is for systems fed from low pressure distribution without a regulator. My mistake.

Regarding length and size of piping. The chart you provided just says "distance". Not sure if they mean equivalent length of pipe? The heater is physically about 70 feet from my meter. But I'm used to looking at equivalent length of piping including pressure drop of fittings etc. It's buried, so tough to know for sure, but my best guess is that I have about 75 feet of actual 1-1/4" straight pipe installed plus about 10 fittings. Assuming 5 ft equivalent straight pipe per fitting = 125 equivalent feet of pipe. The charts I looked at seem to indicate that I'm borderline for 350 MBH at that equivalent pipe length and in a fresh install I would upsize the pipe. Realizing this is what sent me down this path. My beginning logic was that a 350 MBH was presumably operating fine here for 20 years so a new one should be fine. When I looked at the cuts for the new Hayward it seemed to have the same gas pressure requirements as the old one which reinforced this logic. However Raypak (which I was leaning toward) wants 1.5" more at it's regulator. This gave me pause. I figured the lower pressure requirement of the Hayward would help offset the impact of the undersized pipe a bit. Is that logical?

Regarding the actual gas pressure being supplied. I'm working on that. My plan is to measure the static pressure at the inlet to the regulator with the heater's regulator closed and then force the regulator open by jumping the 24v (as recommended by Allen) and measuring the dynamic pressure with the valve open. Is it ok to assume the readings will be valid even if there is no flame? I guess so right? The gas will still be forced thru the burner orifices. I'll let you know the readings when I'm done. Weather been bad, haven't had the chance yet.

Sorry for the long post. I find it very helpful "talking" thru this with all of you. Thank you so much for your help.

Ron
 
rscam said:
my best guess is that I have about 75 feet of actual 1-1/4" straight pipe installed plus about 10 fittings.
Click to expand...
If we use 3.45 feet per fitting for 10 fittings, then that is 34.5 feet + 75 feet = 109.5 feet.

It's borderline.

You can maybe drop down to a 250,000 btu/hr heater or maybe switch the regulator and meter to a 2 psi service and run 2 psi to the heater and use a regulator near the heater.

You would need to use a regulator between the meter and the house service line to drop down to about 7" w.c for the house.

If you put in a 350,000 btu/hr heater on the existing regulator and meter, make sure that the pressure does not drop by more than 1" w.c and that it does not drop to below the minimum.

At about 115 feet, you can get about 367 CFH based on the table.

At 110 feet, you can get about 362 CFH at 0.5" w.c pressure drop based on the calculator using an I.D of 1.38" for 1-1/4" pipe.

At 110 feet, you can get about 386 CFH at 1.0" w.c pressure drop based on the calculator using an I.D of 1.25" for 1-1/4" pipe.

As long as the meter puts out 7" w.c, the heater should get at least 6" w.c.

What is the CFH of the meter from the meter label?

1678893080160.png

1678894024062.png

1678894250847.png

Natural Gas - Pipe Sizing Calculator

Calculate capacities and dimensions of natural gas pipe lines.
www.engineeringtoolbox.com www.engineeringtoolbox.com

Natural Gas Pipes - Low Pressure Capacities vs. Size

Sizing low pressure natural gas pipe lines - Imperial units.
www.engineeringtoolbox.com www.engineeringtoolbox.com

1678894342447.png
 
Last edited:
JamesW said:
If we use 3.45 feet per fitting for 10 fittings, then that is 34.5 feet + 75 feet = 109.5 feet.

It's borderline.

You can maybe drop down to a 250,000 btu/hr heater or maybe switch the regulator and meter to a 2 psi service and run 2 psi to the heater and use a regulator near the heater.

You would need to use a regulator between the meter and the house service line to drop down to about 7" w.c for the house.

If you put in a 350,000 btu/hr heater on the existing regulator and meter, make sure that the pressure does not drop by more than 1" w.c and that it does not drop to below the minimum.

At about 115 feet, you can get about 367 CFH based on the table.

At 110 feet, you can get about 362 CFH at 0.5" w.c pressure drop based on the calculator using an I.D of 1.38" for 1-1/4" pipe.

At 110 feet, you can get about 386 CFH at 1.0" w.c pressure drop based on the calculator using an I.D of 1.25" for 1-1/4" pipe.

As long as the meter puts out 7" w.c, the heater should get at least 6" w.c.

What is the CFH of the meter from the meter label?

View attachment 477301

View attachment 477302

View attachment 477309

Natural Gas - Pipe Sizing Calculator

Calculate capacities and dimensions of natural gas pipe lines.
www.engineeringtoolbox.com www.engineeringtoolbox.com

Natural Gas Pipes - Low Pressure Capacities vs. Size

Sizing low pressure natural gas pipe lines - Imperial units.
www.engineeringtoolbox.com www.engineeringtoolbox.com

View attachment 477310
Click to expand...
Meter is 425 CFH. I posted pic. Connected appliances 350 pool heater, 40 domestic water heater, 20 gas dryer, about 70 I think for stove/oven when oven and all burners are on together. So 480 connected. Assuming some diversity I think that's reasonable. You agree?
 
Seems like it is probably ok.

The regulator can be increased to 7" w.c if it is less than 7" w.c.

Once the new heater is in, verify that the pressure is not dropping below the minimum.
 

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