Not really needed in a closed hydronic system.

Copper does not corrode all that much, and steel or cast iron corrode until the circulating water has no more oxygen dissolved, then corrosion stops.

It is limited by the oxygen in the fill water being consumed in reactions (and one of the reasons you want to keep the same water as long as you can).

I know one older guy who drains his system when he needs to into a plastic trash can, then uses a small pump and to refill the system.

One of the purposes of antifreeze is also to increas the boiling point of the water-antifreeze mix.
This allows the system to run hotter under pressure.

Residential hydronic systems do not normally run with much more pressure needed than to get water to the highest radiator, and the temp is limited to around 180 F.

The pressure in the boiler at the lowest point is the weight of the column of water in the system, and just a few more PSI usually.

This post was edited by brickeyee on Mon, Dec 17, 12 at 16:28

I would look into measures to ensure air and dirt elimination from your hydronic system.

SR

After a bit of research on-line (and a lot of work under the house) I have learned a few things. As Brickeyee pointed out above, the enemy of hydronic systems (and iron pipe) is dissolved oxygen. Once that's gone, rust can't happen....

First bit learned: Sharkbite fittings are really neat, and a damn sight better than soldering over your head in a crawl space.

For system cleaning and subsequent inhibition treatment, about the only company that deals in consumer-sized chemicals as opposed to tank car quantities, is Rhomar Water Management. Unfortunately, their MSDS literature doesn't list what chemicals are involved.

Last bit: you want the pH of the system fluid to be on the order of 7 to 8.5, slightly basic....

Cheers