I want to replace exactly the heater I have now and you have so many to choose from. I want to stay with Raypak. I currently have a 399,999 Natural Gas. My model number is C-R405 EN. The gas on the left of the and the inlet- outlet on the right.I see one that is millivolt and one electronic...wanting to stay with something that my pool man can just slide in place and hook up. I have an Aqualink RS4 panel inside my house to control.