LsFarm wrote:I have run O2 permiable tubing in two different hot floor systems, one I put in about 25 years ago, and my current one.. Both systems work fine,, not corrosion, pumps sit during the summer, and start fine in the fall... and they are cast iron pumps not bronze.
The trick is to have pressure on the system,, and to pump [push] the water through the tubing, don't pull the water from the tubing. Any amount of negative pressure allows the O2 to migrate through the tubing.. but under pressure this is either eliminated or so minor to be not an issue..
As for you hot water coil providing enough hot water for your floor heat,, I'd use the above formulas and give it a run through your calculator...
OR: Just give it a try... try the hot water coil and see if it provides enough BTU's..
The other option is to run the floor heating system through a water/water heat exchanger, and use the regular hot water from the boiler... a 40 plate water/water exchanger can be purchased for around $200 on Ebay,, [search outdoor wood boiler] and this size exchanger is good for around 150K BTU, if I remember correctly. Maybe 180K btu.. Piping is simple,, and you could add a fresh anti-corrosive,, such as automotive ethylene glycol or propylene glycol. in the isolated floor loop.
I use the plate exchangers in my systems,, they work great,,
My experience with oxygen permeable tubing used for in floor heating is very different. I had extreme corrosion, including the cast iron pumps. I resolved the problem by isolating the oxygen permeable part of the system with a flat plate heat exchanger and, when I continued to have corrosion problems with the cast iron pumps in that part of the system, by replacing the pumps with bronze ones. I had the problems notwithstanding the fact that my pumps were set up to push.
With regards to ethylene and propylene glycol--without inhibitors these will very quickly turn acid when used in a heating system. Commercial anti-freeze based on either product includes inhibitors. However the inhibitors are consumed over time and standard practice is to replace the fluid (replacing the anti-freeze in a car every few years for example). It is possible to replace the inhibitors but they are not widely available and it takes testing materials to determine appropriate replacement intervals and doses.
For a home heating system I would strongly recommend isolation of oxygen permeable tubing using a flat plate heat exchanger and replacing any ferric materials in the portion of the system that has the oxygen permeable tubing. If you want an additive for portions of the system containing ferric metals I would suggest a product like 8-Way™ http://www.rectorseal.com/index.php?site_id=1&product_id=172