SPA heater, what would happen?

[Hulaomr]

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.

For example, 1,202 gallons of water is about 10,000 pounds of water.

So, a 1,202 gallons spa should gain about 33.6 degrees F per hour.

After fix the temperature issue with the thermistor, I performed other tests adjusting the maximum temperature. During the first test, the heater stopped heating once it get to 35C. During the second test, it stopped heating once it get to 38C (which is the maximum I set with the board button).

As reference, below the results for the second test:

• The temperature changed from 34C (12m:08s) to 35C (14m:10s) in 2m 4s
• The SPA has 580 gallons (the pool pump which add water to the SPA was off).
• The SPA pump was set to 60GPM
• The temperature get around 36C at the SPA

“Direct Air Intake Duct with 3-inch PVC Pipe (Indoor Installation)”

 

[Hulaomr]

• The temperature changed from 34C (12m:08s) to 35C (14m:10s) in 2m 4s
• The SPA has 580 gallons (the pool pump which add water to the SPA was off).
• The SPA pump was set to 60GPM
• The temperature get around 36C at the SPA

@JamesW please, may you let me know if these values make any sense?

 

[JamesW]

The temperature changed from 34C (12m:08s) to 35C (14m:10s) in 2m 4s

34 = 93.2 F to 35 = 95 F, which is 1.8 degrees or 0.87 degrees F per minute, which is low.

However, it is not accurate due to the resolution of the temperature sensor.

You need at least 30 minutes to really tell how fast the water is heating per minute.

• The SPA has 580 gallons (the pool pump which add water to the SPA was off).
• The SPA pump was set to 60GPM

For 580 gallons, you should get about 70 degrees F per hour or about 1.16 degrees F per minute.

The SPA pump was set to 60GPM

60 gpm = 11.2 degrees F temperature rise from before the heater to immediately after the heater.

For example, if the Inlet is 90°F (32.2 °C), the outlet should be 101.2 °F (38.4°C).

So, at 60 GPM, you should see a 6.2 degree °C temp rise from inlet to outlet.

 

[JamesW]

For 580 gallons, you should get about 70 degrees F per hour or about 1.16 degrees F per minute.

For example, if the water starts at 69 F (20.6°C) and you run for 30 minutes, you should get about 35 degrees F increase to 104 F (40 C).

You should get about a 0.65 °C per minute temperature rise in the spa. (40°C - 20.6°C = 19.4°C in 30 minutes).

(69°F − 32) × 5/9 = 20.556°C

(104°F − 32) × 5/9 = 40°C

 

[JamesW]

The temperature changed from 34C (12m:08s) to 35C (14m:10s) in 2m 4s

That is 0.48°C per minute compared to about 0.65°C per minute for the expected rise.

In 124 seconds, the expected temp rise is about 1.34°C, but the temp sensor only registers whole numbers, so you won't see a change until it gets to 2 degrees at about 185 seconds or about 3 minutes and 5 seconds.

You should see about 2°C for every 3 minutes of operation.

Did you figure out anything about the gas meter and why that is not adding up?

 

[JamesW]

I suppose the voltage reading was affected.

It affects the resistance, which affects the reading.

During a test, the device reported 142C (287F).

Here is what the normal exhaust temperature should be:

• Below 250 degrees...very low
• 250 to 290 ..................low
• 290 to 350.................acceptable
• 350 to 480 ..................high
• Above 480...................error/shutdown.

287.6 is close to being acceptable.

 

[JamesW]

1 cubic meter of propane produces about 88,905 btu.

17 cubic meters of propane is 1,511,378 btu.

17 cubic meters of propane in 34 minutes is 2,667,150 btu/hr, so that is probably not correct.

Maybe the meter is not accurate?

You should use about 4.5 cubic meters of propane per hour for a 400,000 btu/hr heater, which is about 0.075 cubic meters per minute.

You should use about 1 cubic meter per 13.3 minutes.

You are using about 30 cubic meters per hour, which is about 6.67 times more than expected.

Here are some possible explanations.

1) The meter is way off in measuring the flow of propane.

2) The reporting units are something other than cubic meters.

The problem is that I cannot find any units that would match the usage.

30 units of Propane would need to have about 13,333 btu per unit and nothing matches that metric.

Cubic foot: One cubic foot of propane contains around 2,516 BTUs.

Gallon: One gallon of propane contains approximately 91,500 BTUs.

Pound: One pound of propane contains approximately 21,548 BTUs.

3) Maybe there is a gas leak.

 

[Hulaomr]

The meter is way off in measuring the flow of propane.

The meter is new and previously calibrated at gas provider. I saw when they installed from the carton and it look new.

I have a 20kBTU boiler at home. Perhaps, I could perform a test to compare?

 

[Hulaomr]

Maybe there is a gas leak.

The meter is not moving while the heater is off. At heater location I don’t smell any gas. At the beginning when the heater was not turning on, I could feel the smell, but now, I cannot feel it.

 

[JamesW]

I have a 20kBTU boiler at home. Perhaps, I could perform a test to compare?

That would take about 4.45 hours to use one cubic meter of propane.

 

[JamesW]

17 cubic meters of propane in 34 minutes is 2,667,150 btu/hr.

There is no way that the heater is using that much gas.

Maybe have the gas company check it out.

 

[Hulaomr]

Maybe there is a gas leak.

The gas head that goes inside the heater, which is different from natural vs propane gas, could be the issue?

Perhaps it was changed from propane to natural gas (assuming the Propane requires smaller orifices).

 

[JamesW]

https://heathungary.hu/doc/gazmerok/membranos/sensus/sensus_mr8.pdf

 

[JamesW]

1 cubic meter of propane produces about 88,905 btu.

The meter started at 5.7 cubic meters and went to 7.4 cubic meters.

In 34 minutes, you used 1.7 cubic meters (Not 17 cubic meters).

That is 3 cubic meters per hour, which is 266,715 btu per hour.

So, you are using about 67% of the expected amount of gas.

 

[Hulaomr]

@JamesW, wuaoo, good catch. My bad.

So, you are using about 67% of the expected amount of gas.

This efficiency make sense?

 

[JamesW]

You should be using about 4.5 cubic meters of gas per hour, but you are using only 3 cubic meters, so there is a problem somewhere.

 

[JamesW]

Maybe the gas valve is defective.

Check the orifice diameter.




Pentair/Sta-Rite Combination Gas Valve, MasterTemp/Max-E-Therm #42001-0051S

MODEL 36D27-902

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[JamesW]

 

[JamesW]

The orifice should be stamped BL

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/heaters/mastertemp/manual/mastertemp-heater-manual-english.pdf

Pentair 77707-0441 Gas Orifice Kit 400K LP

 

[JamesW]

The "B" means 400,000 btu/hr and "L" means Liquid Propane.

"N" means Natural Gas.