Water flow thru heater to get best heating

[gary300]

Another way to look at it is this...Think of it as if you are trying to cool the heater instead of heating the water. What would work better, low flow or high flow. Now as far as how fast to run the pump. At some point the heat absorption by the water thru the heat exchanger will level out. Put a thermometer in front of the return to the pool and measure the temp of the return water. Note that and turn the speed on the pump up and measure again. The return water temp should drop slightly. Keep increasing the flow untill the water temp no longer drops at the return. This is the ideal pump speed for max heat transfer into the pool. anything faster and you are just going to use more electricity and not gain any BTU load into the pool.

That sounds like a good test. I will need to rig up something to measure the return water temp

 

[mas985]

At some point the heat absorption by the water thru the heat exchanger will level out.

This is not true. The water temperature will continue to drop with increasing flow rate so I don't see how this is helpful. With a 400k BTU heater and even at 100 GPM, the heater will add about 6 degrees of temperature. The flow rate would have to be over 10x that before you would see less than a 1 degree change.