Hey tip been in the biz for 20 years have seen a lot but you know there is always something lurking you haven't experienced yet. Well here is my mind buster for the day.... Have pool/spa combo with a Jandy jxi heater installed 400K Nat Gas - Here is the issue the heated water never reaches either the pool or the spa with good circulation?? swapped out therm regulator and bypass to no avail - found the water hot when removing the drain plug from the heater but it seems never to transfer to either body of water.... any suggestions ideas are welcome
Spa and pool heat
- Thread starter 5starpools
- Start date
- Jun 24, 2021
- 16,081
- Pool Size
- 29000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60 Plus
To confirm, when you put your hand in the return flow (like in front of all returns), you don't feel warm water? Can you feel any warmth on the return piping after the heater?
Does the vent terminal housing get hot? Have you confirmed the heater is firing?
What is the ignition Control LED status?
Do you get any service diagnostic codes?
Have you confirmed that there is at least 30GPM flow?
Post a picture of the equipment pad if you have one.
Can you check the heater outlet water temp?
Is there a salt water chlorinator after the heater?
If yes, see what the cell temp is.
Subtract the Inlet Water Temp from the Outlet Water Temp to get a Temp rise.
The heater should produce about 400,000 btu/hr.
The heater is about 84% efficient, which transfers about 336,000 btu/hr to the water.
1 btu adds 1 degree F to 1 pound of water.
You can get a water temperature from the heater for the inlet, which is the spa water temp.
If you can get a water temp at the heater exit, you can calculate the temperature rise.
Exit temp - inlet temp = temp rise.
If you know the flow rate, you can calculate the expected temp rise.
For example, 40 gpm is 2,400 gallons per hour or about 20,000 pounds per hour.
At 40 GPM, the expected temp rise is about 336,000/20,000 = 16.8 degrees F.
This shows the expected temp rise (Y-axis) vs. Flow in GPM (X-axis).
The minimum required flow is 40 gpm.
So, the maximum temp rise should be 16.8 degrees Fahrenheit.
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.
Higher flow results in a lower 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.
You can use this formula to estimate the flow based on the temperature rise.
Y = temperature rise.
X = flow in gpm.
Y = 672/X
X = 672/Y.
For example a flow of 40 gpm should be a temperature rise of 16.8 degrees.
A temperature rise of 11.2 degrees should be about 60 GPM.
As you can see, flow below 40 gpm results in a big temperature rise.
www.wolframalpha.com
Is there a salt water chlorinator after the heater?
If yes, see what the cell temp is.
Subtract the Inlet Water Temp from the Outlet Water Temp to get a Temp rise.
The heater should produce about 400,000 btu/hr.
The heater is about 84% efficient, which transfers about 336,000 btu/hr to the water.
1 btu adds 1 degree F to 1 pound of water.
You can get a water temperature from the heater for the inlet, which is the spa water temp.
If you can get a water temp at the heater exit, you can calculate the temperature rise.
Exit temp - inlet temp = temp rise.
If you know the flow rate, you can calculate the expected temp rise.
For example, 40 gpm is 2,400 gallons per hour or about 20,000 pounds per hour.
At 40 GPM, the expected temp rise is about 336,000/20,000 = 16.8 degrees F.
This shows the expected temp rise (Y-axis) vs. Flow in GPM (X-axis).
The minimum required flow is 40 gpm.
So, the maximum temp rise should be 16.8 degrees Fahrenheit.
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.
Higher flow results in a lower 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.
You can use this formula to estimate the flow based on the temperature rise.
Y = temperature rise.
X = flow in gpm.
Y = 672/X
X = 672/Y.
For example a flow of 40 gpm should be a temperature rise of 16.8 degrees.
A temperature rise of 11.2 degrees should be about 60 GPM.
As you can see, flow below 40 gpm results in a big temperature rise.
plot Y = 672/X, y from 6 to 60 - Wolfram|Alpha
Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com
Check the exhaust temp with a non-contact temperature sensor.
Check the gas usage during operation and it should use about 400 cubic feet per hour or about 6.67 cubic feet per minute.
One cubic foot of natural gas contains approximately 1,036 British Thermal Units (BTUs).
If the heater is running, the heat has to be going somewhere.