Happy to be here, I've been lurking for a bit. In July 2019 we bought a 2400 SF ranch in the thumb of Michigan with a walk out basement , it has a 20 year old P057 2 stage WaterFurnace Premier open loop, dumping to a creek. I've got the original book(s), and found an updated 2001 book on this site. There is no matrix to go down and across for performance diags, the pressure, temp drop and GPM charts are very basic. I have many questions, but I'll take this in stages. The furnace seems to be doing it's job, but I believe the efficiency could be better. My 1st question is what should I use to clean the air coil and the coax. I've read Formula 409 is safe and effective on the air coil, I have a pump setup I used on my tankless water heater so I'm looking for recommendations on the chemicals for the coax. This will wait till spring, I don't need any drama during the winter. We have very good water, but there is a small amount of iron, it shows up at the hose bibs if they're not shut tight. Any guidance is greatly appreciated.