GPM for Mastertemp 250?

[kul]

Hi TFP, how do I calculate my GPM? Or is there a place to view this? When my pump runs, I can just see the pump speed which I run typically at either 1500 or 2400. What is the lowest speed I can run my pump so that the mastertemp 250 can function appropriately?
I haven’t had any issues running it at 1500 or even 2400 to heat just my spa, but I thought I’d check. I don’t use the heater too often. Have attached some photos of my pump in case that’s helpful. My filter is a Pentair Cartridge clean and clear 320 in case that makes a difference.

 

[mas985]

Most heaters work on pressure rather than flow rate. The simplest way to find the minimum RPM is to lower it until the heater throws an alarm. The heater should tell you when there is an issue.

 

[ajw22]

Pentair says you heater needs a minimum of 25gpm. I have found that to be conservative.

To check you have sufficient flow and not damaging the heater put your hand around the water manifold and the output pipe. If they are luke warm to the touch and not hot then you have sufficient flow carrying off the heat.

Your pump at 1500 rpm is likely doing 20-25 gpm or more. I run my MasterTemp 400 at 1700 rpm with no problems.

Less flow gives a higher water output temperature at the returns. So make sure the water at the spa returns is a comfortable temperature or increase the RPM and flow to get the water output cooler. You still get the same heating with cooler water at a higher flow.

 

[kul]

Thanks @ajw22 is there any way to know for certain the Gpm? Is there somewhere on the Pentair pump I can look while it’s running?
The temperature at the output pipe is warm, but not hot. The water coming into the spa at the jets is comfortable at the low (1500) and higher (2400) rate.

 

[ajw22]

Don’t worry about the flow. Your temperatures sound fine.