Does anybody know of a good additive to condition the circulated water in a radiant heating system?  Looking for something that contains a water pump lubricant, oxygen scavenger, rust preventative, etc.

None of this is necessary for residential hydronic systems.

Hi Badger,

Thanks for the reply. My system is not standard. It is not a pressurized system.

I have had problems with the circulating pump seizing on me. My water is very hard and there were heavy deposits on the pump. I had a softener installed and replaced the water in the system. Thought this would fix it, but it didn't. I'm thinking of draining and refilling again. I can't remember if drained the loops the first time or just the 100 gal tank.

Any thoughts?

This is an "open" heating AND domestic hot water system then?

Nope. DHW is separate.

I have ground loops supplying two heat pumps. One water to air - feeds ductwork and supplies heat and cooling.

The other water to water unit warms water in a 100 gal. plastic tank. The tank is not pressurized. Has a 8" screw cap with a small vent to atmosphere. When the water gets below ~95F a pump circulates this water thru the heat pump to warm it. Shuts off about 115F.

This tank supplies PEX (non-O2 barrier) floor loops, heat only. When a tstat calls for heat, a zone valve opens (3 zones) and the end switch kicks in a circulator pump. This pump has been giving me problems. It's an iron Grundfos. I'm worried about rust, minerals and nasties growing in the water.

Thought there might be an additive to help.