Low Inlet Pressure to Hayward 400K natural gas heater

stephenson

Well-known member
Nov 30, 2009
136
Hi All,

Second thread this week :)

Hayward 400K BTU heater, house/pool/heater built 2017/2018.

Had trouble getting the gas heater to stay lit when we first moved in so took it apart to clean everything. Dust and dirt, but no other indications of issues, so put it back together and fired up and fine and runs fine, but is EXPENSIVE to operate.

Kept smelling NG so got my manometer out and checked the output side of the valve - see photo. 1.46-1.50", depending whether case sealed or not. Tried adjusting, but would not go above 1.50 - I COULD adjust it down, though, and could feel the stop at the far counterclockwise position.

So, shut it down, secured valves and pump, and sealed outlet cap up using sealant on threads.

Checked inlet with heater off - see photo. 8.94" static pressure to inlet.

Started it up, and inlet pressure dropped to 2.56".

Typically this mean either the pressure is set too low at the main meter, or the meter itself is too small, or the lines are too small to the appliance.

I am gonna take a stab at the scenario - house was built in late 2017 and has a tankless water heater, and stub for outside cooktop, but no other gas appliances. Then pool built a couple of month later. Heater is HUGE for the size of the pool (10x20 kidney shape with max 5 1/2' depth on one end), but installing company says they install the same size regardless of pool (sigh). Installer tested without testing pressures (inlet and outlet plugs were incredibly tight and had no sealant), it started and ran ... ta da ... and left. First owners not particularly clueful about the pool and didn't use it except one summer (Florida).

So, first call to gas company to check sizing on meter?
 

ajw22

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Photos not adding normally, so here are hopefully one at a time.

Photo upload is broken at this time.

 

ajw22

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Your gas meter should have a data plate or markings on it for the CU FT it supports. It may or may not look like this...

91bc683b9d93091d67daef6c6f8f0230.jpg


Here are threads about gas meter sizing...

 

stephenson

Well-known member
Nov 30, 2009
136
Thanks, ajw.

Read several of the threads.

My meter is 275 CFH, CL250 (Sensus brand).

Looks like 3/4" line and fittings in, then 3/4" out to T where 3/4" goes to side of house where it changes to 1", with the other end of T going to 3/4" and to ground where it looks like it goes to 1" at a coupling.

At the heater I comes out of the ground at 1" then goes to 3/4" and then through valve and coupling and stays at 3/4" into the heater.

The other appliances at the time of the house build (and, likely meter install) were: Rinnai tankless (199K BTU), and a stub for back porch cooking that has never been used. No other gas appliances.

The Sensus R-275 has a capacity of 275 ft3/h. The heater is 400K plus the 200K for the Rinnai water heater, so 600K BTU. Converting, then, 600/100 = 6 therms x 96.7 = meter throughput if both appliances running of about 580 CF/hour.

So, way undersized meter.

How about the piping? A very quick and unqualified look at gas pipe sizing charts seems to indicate the 3/4" lines are all undersized by 1/4-1/2"?
 

ajw22

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Yup, you are way undersized. @JamesW posted various gas flow numbers in those other threads.

Basically you need to have your gas company upgrade your gas service and then do some new piping from the meter to the heater. If they can T a gas line after the meter that runs to the pool heater and then the house feed stays as is. No rocket science to it, just $$$s.
 

ajw22

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Does the gas output line running into the ground run directly to the heater?

You need to contact your gas company and see what is involved in upgrading the gas service.

@JamesW @swamprat69 @MITBeta

1TW1LxKvw-EBq6CiieGARizztAbW0EmlM=w2000-h1298-iv1


1tGLec7kIycldjrv7IpZMRdzKFXq87435=w2000-h1298-iv1


1rJfJlAQS-tHkZX_9BfdmXCVdt4cvpdCR=w2000-h1298-iv1


1q9EiaD5yBeVqONMAZc5oDYkRb5yF91jv=w2000-h1298-iv1


1AMSmF6onYIclynK1Zl5Sb_MIfDvjGq2x=w2000-h1298-iv1


1WXsK22WEyg2BsjR64uSdJKyPU_7C5m1N=w2000-h1298-iv1
 
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JoyfulNoise

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Thee should not be two regulators on the meter. Someone did not properly plumb that gas main.
 

JoyfulNoise

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And the gas company can probably hook your pool line up to the high pressure side and the do a regulator at the heater.
 

stephenson

Well-known member
Nov 30, 2009
136
Joyful, not sure what pressure they have coming to the first regulator, or why a second one would be needed ...

Couple of different ways, it looks like - all relate in some fashion to the need for two different regulators.

If can keep smaller diameter line to heater, and put regulator there would be easiest fix, it seems like - T just after the outlet leaves the meter, but before the regulator - then another T from the regulator for the water heater and (stubbed out) outdoor cooking.
 

JoyfulNoise

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Call in your gas company to sort it out, even if it costs you a service charge. Every residential meter (or most) should have both a high pressure port (~2 psi) and a low pressure port (~ 14" WC or so). Most household appliances only need a few inches to operate and so one typically installs a regulator right at the appliance if it doesn't have an internal regulator. Your pool heater can operate from the low side of the meter BUT the pipe diameter and run length must be properly spec'd so that there isn't a big drop in pressure when the unit is running (which seems to be exactly what is happening to you). For example, my gas meter and pool heater (400kBTU/hr) are over 150 feet away from each other. Therefore, when my pool was installed, the plumber ran 2" diameter gas line from the meter to the pool heater and necked it down to 3/4" pipe where it entered or exited the ground. There is also a 2"x1" tee for a run to the gas fire pit and BBQ island. The low pressure works precisely because my buried pipe is a huge diameter. If it were any smaller, my gas heater would never run properly as it would be starved of gas. Now the other option a pool plumber has is to run a smaller diameter pipe to the heater but use the high pressure (2psi) side and then install a regulator at the heater to bring the service pressure down to 11" WC or so. Usually when one has long runs or a yard that cannot accommodate a large buried low pressure pipe, using the high pressure side works better.

If I had to guess what the last homeowner did there was that they supplied all the appliances in the house using a run off that second regulator to ensure that the correct pressure reached the tankless heater and anything else in the house that uses gas rather than putting separate regulators at each appliance. Whoever did the pool put a tee in on the wrong side of the second regulator. The regulator that is on the input side of the meter was put there by the gas company. It reduces the street pressure (usually around 5psi or so) down to the appropriate operating pressure for the meter.

Don't touch anything until you've had the gas company take a look or, in some municipalities, a gas plumber that is registered and approved by the gas supply company to work on residential lines.
 

stephenson

Well-known member
Nov 30, 2009
136
All,

Put together email to our local supplier - they responded by phone this morning. They suspected the meter was never changed after the pool heater was installed. Discussing whether installers actually checked pressures, the fellow said, "Um, they put in generators, heaters, pool heaters, if it starts they show the homeowner it works and leave."

Sent them photo, and the fellow set up appointment to swap the meter out. Great response!

Follow up questions:
- how much gas smell would be normal for this sort of heater (we get some on startup and sometimes can smell it for a few minutes)
- could the smell be related to the low inlet pressure?
- could the smell be related to the low outlet pressure?
- is there an efficiency factor associated with the lower inlet and low outlet pressure?
- I have read that there might be increased condensation if outlet pressure is low?
- anything else one would expect to see with low inlet and outlet pressures?
 

ajw22

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I have never had a gas smell around any of my gas pool heaters. I don't think a gas small is ever normal in operation. Especially with a forced draft heater like the Hayward.

Low gas pressure will cause the heater to run lean. It will not generate the rated BTUs with less gas.

You may get corrosive condensation with the heater running cooler then designed.
 
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JoyfulNoise

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Can you please update your signature with your list of equipment including any model information? It helps us help you a lot better.

Just so you know, there is no heater that is "too big" ... the size of the heater simply determines how quickly the pool will heat up. It requires the same amount amount of heat energy to heat a body of water to a certain set temperature no matter what. A smaller heater just takes longer than a bigger heater but the amount of gas used is the same. In other words, a BTU (British Thermal Unit) is the amount fo energy required to heat 1 pound of water by 1 degree Fahrenheit. So a 400,000 BTU per hour heater will heat your pool twice as fast as a 200,000 BTU/hr heater .... the amount of gas used is exactly the same.

As @ajw22 said, low pressure will cause the flame tray or combustion chamber to run lean. Running lean will mean less BTUs and therefore take longer to heat the pool.

Sometimes you might smell a whiff of gas at startup but it should go away quickly. If it's lingering or you smell gas when the heater is not running, then the gas valve may be bad. It's not easy to diagnose this when there is already a supply pressure problem. Get that fixed first and then see how the unit is working.

Also, make sure the contractor that does the work is willing to fully check the heater while it is running (this usually takes someone with gas plumbing experience and the proper test equipment). There should be a procedure in the heater's manual for testing both the static line pressure (heater OFF) as well as the pressure when the heater is running and the gas is flowing. The heater manual will have spec's (our should) for both the static and dynamic gas pressure. I'll say that most forced-air type gas heaters have gas control valves that typically need a minimum gas pressure above 4" WC when running with 7-9" WC while running being optimal. A static gas pressure at 11-14" WC is fine at startup.
 

stephenson

Well-known member
Nov 30, 2009
136
Right - (all " WC) my static line pressure is 8.94, and when running drops to 2.56 (spec is 4.5-10.5). The outlet pressure is 1.46-1.50 (spec on earlier Haywards looks to have been 1.8-2.0, but mine is 2.0 without a range), but could not be increased above 1.46-1.50 range even with full clockwise rotation to the stop. It could be adjusted down, however, stumbling at around 1.35 or so - this was close to the stop at the counterclockwise position.

And, yes, I understand the size discussion - this being Florida, and 400K units being more expensive than 200K units, it just seems a bit odd to simply install 400K. I understand the goodness of having a single solution always on the truck - logistics, common components, etc.
 
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JoyfulNoise

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Yeah. If you’re only getting 2.6” while running, that’s way too lean. Your heater is not putting out the full BTUs. Hopefully a meter upgrade with some replumbing will get you better pressure.

As for equipment - buy the biggest sizes your budget can afford is the typical mantra around here. Florida pools always seem to have equipment pads outfitted with the smallest equipment possible. Our TFP Mods and Guides can always tell a Florida pool just by looking at the pad.
 
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