In reading the instructions, I understand it's best not to install the cell upstream of the heater due to the increased concentration of chlorine the heater will be exposed to. That makes sense. That takes a lot of options away so I'm at a loss now. I have no clue why the return line leaves the filter at 2" and reduces down underground before it gets to the heating input at 1.5". If I install it just after the heater output, the unit will have to be upside down due to how the flow switch is installed. Now I see that's one downside to a cell unit that has all the diagnostic readouts rather than in the power unit. I guess in a pinch, I can live with it being upside down. Option 2 would be to plumb it into the line where I have the flex hose bypass that used to go through the booster pump for the polaris that we don't use anymore. Any problem with the chlorinated output only returning on that single line? The return from the heater splits to three returns. Any other ideas? I'd appreciate it.