Raypak R406A (399K BTU)

[asondhi]

I have a 41 x 21 salt water pool. Just replaced an older Raypak gas heater (at least 5 years old) with the Raypak R406A (399K BTU). When I put my old heater on 90 degrees, the return lines and my water feature would bring very hot water back to the pool. With the brand new unit, the water returning to the pool is lukewarm at best, even if I set it at 90 degrees. Any ideas as to why?

The water started at 72 degrees and after 1 1/2 - 2 hours it went to 73.

Thanks.

 

[JamesW]

The temperature rise depends on the flow rate.

What is the flow rate?

What was the btu/hr of the old heater?

Are the gas supply line and meter big enough?

Is the pool covered?

Check the gas meter and watch how much gas the heater is using.

It should use about 1,000 cubic feet of natural gas per 2.5 hours.

Is the heater natural gas or propane?

 

[JamesW]

When I put my old heater on 90 degrees, the return lines and my water feature would bring very hot water back to the pool. With the brand new unit, the water returning to the pool is lukewarm at best, even if I set it at 90 degrees.

Note that the set point does not affect how much heat is going to the water.

The temperature rise from inlet to outlet depends on the btu/hr and the flow rate.

The minimum flow rate is 40 gpm for a 400,000 btu/hr heater.

At that rate, the temperature rise is about 16.8 degrees.

So, the water exiting the heater should never be more than 16.8 degrees warmer than the water entering the heater.

(400,000x.84)÷(40x60x8.34) = 16.8 degrees.

For all heaters, the minimum flow rate is 10 gpm per 100k btu/hr. At that rate, the temperature rise is about 16.8 degrees.

Target flow rate should be about 5 to 10 gpm above the minimum for margin of error.

Can you describe all of the equipment that you have?

If you can get a temperature reading downstream from the heater and a flow rate, you can use that to estimate the heat transfer to the water.

 

[JamesW]

The water started at 72 degrees and after 1 1/2 - 2 hours it went to 73

(400,000x.84)÷(30,000x8.34) = 1.34 degrees per hour.

Assuming a pool volume of 30,000 gallons, you should expect about 1.34 degrees per hour.

Due to the precision of the temperature sensors, you can't go by one or two hours. You need at least 10 hours to get a good idea of the heat gain rate.

However, you can also lose heat if the pool is uncovered and it's cold and windy outside.