Hayward H135 Return Water Temp Low??

kennywayne34

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Hello and thanks in advance for reading. We are 1.5 seasons in on our Heyward H135 Natural gas heater. Up until a few weeks ago the return water was extremely warm. We have a fountain feature that if you stood beneath it it felt like a hot shower. Now the water is not as bad as "luke" warm but no where near the temps it once was. This seemed to just happen overnight with no gradual loss. I am at my wits end trying to figure out why this is not as efficient as we are used to. and ready to call in help "gasp" My trouble shooting is as follows. I'm starting to wonder if the bypass valve is passing or if the gas regulator needs adjustment. I do not have the pressure gauges to run water column pressure tests although I don't know why this would need adjustment all the sudden.


1. No error Codes thrown and fires up no problem
2. Complete disassemble of heat exchanger for visual inspection. No Deposits noted and water was free flowing from hose through the tubes
3. Complete disassemble of the burners , gas line header and orifices- no spider webs fouling or scale build up on burners ETC
4. no gas leakage at any of the hard pipe gas line joints tested via Windex bubble method
 

ajw22

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Did you change your pump or the speed you run your pump?

Higher water flow will give you lower water temperature output from your heater.
 

kennywayne34

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Thank you for that! Actually no but I did acid wash my cartridge filter this season due to a high cottonwood this year and the pressure seems a bit harder. But again it wasn’t like it was immediately after the acid wash or a light bulb would have gone off for me I think. Maybe that’s it? Not sure how to de pressure without a re-plumb because the heater will not run with pump on low speed.
 

ajw22

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Your heater BTUs are less then half the example below so take less then half the numbers below. I don‘t know how you got very hot water from your heater unless you had low flow barely above what would run your heater. Your heater is not designed to give an output temperature rise of more then about 7 degrees.

Heater outlet temperature rise will depend on the water flow rate. Slower water flow will have greater outlet temperature since the same BTUs go into less water volume.

Changing the pump speed can vary the return temperature from just warm at high RPM to very hot at minimum flow for the heater.

For example, a 400,000 btu/hr heater with an efficiency of 84% transfers 336,000 btu per hour to the water.

At a minimum required flow of 40 gpm, there will be 2,400 gallons of water (20,000 lbs.) that receives the heat.

Each btu raises the temperature of one pound of water by one degree Fahrenheit.

336,000 btu into 20,000 pounds of water is 16.8 degrees of temperature rise (336,000/20,000).

So, the maximum temperature rise you should ever have is 16.8 degrees Fahrenheit.

As shown below, higher flow results in a lower temperature rise.

  • 40 gpm = 16.8 degrees temperature rise
  • 50 gpm = 13.44 degrees temperature rise
  • 60 gpm = 11.2 degrees temperature rise
  • 70 gpm = 9.6 degrees.
  • 80 gpm = 8.4 degrees.
 

kennywayne34

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Really appreciate the insight. From what I see here it’s more than likely a flow issue. I will say the return pressure is a bit extreme
Any experience with turning the pressure switch dial to work with low speed on pump? I could never get it to work in fear of turning that dial too much. I have read the instructions in the manual. The specs for the pump say there is plenty of gpm even on low speed to operate the heater. I understand there is more into it than the spec gpm output with head pressure etc.
Thanks Again
 
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ajw22

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Show me some pics of your pool equipment and plumbing as well as your pump motor data plate.

What is your filter clean pressure and current PSI?
 

JamesW

TFP Expert
Mar 2, 2011
28,291
The H135ID1 is 82% efficient.

So, it transfers 135,000 X 0.82 btu/hr = 110,700 btu/hr.

GPM........temp rise

20..............11
30..............7.38
40..............5.5
50..............4.4
60..............3.7
70..............3.2
80..............2.8



20 gpm = 1200 gph = 10,000 lbs of water.

110700 ÷ (gpm x 500)

temp rise = 221.4 ÷ gpm

y = 221.4 ÷ x, x from 0 to 80

1627061658175.png
1627061782704.png

The temp rise should not be more than 11 degrees at any point.

Higher flow reduces the temp rise but the amount of heat transferred to the water is not reduced.
 
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JamesW

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Mar 2, 2011
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As you can see from this graph of temperature rise (Y-axis) vs. Flow in gpm (X-axis), the temperature rise goes up very rapidly as the flow goes below the minimum as specified by the manual.

The typical minimum flow rate for a heater is about 10 gpm per 100,000 btu/hr.

So, your absolute minimum should never be below 13.5 gpm.

The manual states 20 gpm as the minimum, so that should be the minimum for your application.

1627062778229.png
 

kennywayne34

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Show me some pics of your pool equipment and plumbing as well as your pump motor data plate.

What is your filter clean pressure and current PSI?
This is best I can do from work. This was early in the build and the swg and Jandy check before swg are not pictured yet. The remainder is the same from pump/filter to heater with by pass. . 2” pvc and it is buried running twenty feet to / from pool. I did this to avoid running utilities underground.
 

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kennywayne34

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Thanks a bunch guys and gals. You all are really the best. I will get more detail on the clean psi and plate when I get home. Just FYI I went home for lunch and turned on the heater. The temp at 11:30 am EST was 81. I set it to the max temp of 90 and is currently running. I will be home between 3:30 and 4:00 est and will report temp increase. I know I know 81 is already warm for some. We like it warm as we live off Lake Erie and it’s only 70 degrees here today. Thanks a lot!!
 
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kennywayne34

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Well I just arrived home and the temp reads 86 degrees. Up 5 degrees in 4 hours. Current psi is 10 and I would say that is a clean psi reading. When it gets to 14 psi is when I feel a clean up is necessary. (Dirty)
 

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ajw22

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Max the heater will give you is about 2 degrees an hour. If you don't have a pool cover you are losing heat with a 70 OAT so a bit over 1 degree an hour makes sense.

We recommend the filter be cleaned when the filter pressure rises by 25%. So more like 13 PSI to clean versus 15. The longer you wait the lower your flow will get.
 

JamesW

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Mar 2, 2011
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24 Round x 54" Saltwater 8000.

15,200 x 8.34 = 126,768 lbs of water.

At 110,700 btu/hr, the rate of temperature increase in the main pool should be about 0.873 degrees per hour.

How did you calculate the pool volume?

Is the 54" the wall depth or the actual water depth?


1627070658124.png
 

ajw22

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I took the 8000 from the signature and assumed it was the pool volume gallons. If it is more like 15,200 gallons then 1 degree an hour makes sense.
 

kennywayne34

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Max the heater will give you is about 2 degrees an hour. If you don't have a pool cover you are losing heat with a 70 OAT so a bit over 1 degree an hour makes sense.

We recommend the filter be cleaned when the filter pressure rises by 25%. So more like 13 PSI to clean versus 15. The longer you wait the lower your flow will get.
Copy that i never went by the percentages it was all feel of the return but will use the percentage logic.
It just seems that the heater is still just working a bit harder or slower than normal even given the OAT
I'm not so much worried about the return temp as long as its efficient
I took the 8000 from the signature and assumed it was the pool volume gallons. If it is more like 15,200 gallons then 1 degree an hour makes sense.
Nope that's the model I can change that to avoid confusion. Its 24 round 54 wall height so the calculator is about right
 

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