Muriatic acid will destroy all your heat exchangers, pumps and metal plumbing. With some metals (like aluminum heat exchangers) you'll get a nice hot reaction releasing large amounts of hydrogen gas. Was that your goal here? :-)
Vinegar (acetic acid) is oft used for descaling, but even that can be somewhat aggressive depending on the concentration. Something with a PH of about 3.0 is fine. Lower than 2.5 may be too much. (5% acetic has a PH of ~2.4.)
Vinegar won't kill legionalla quickly, but will eventually. A 50% vinegar/water solution soak for 30 minutes once/week is part of the sterilization protocol for low-risk legionella sources like indoor fountains, etc. Not sure if it's too much for the PEX, but it will eventually eat all the bronze & copper if repeated often.
Basically, open systems suck- from a heath & maintenance POV. If there's a way to easily re-plumb it in a way to isolate the potable from the heating water, consider it! |