Best Solution for PEX tubing radiant heating system

[Hadrianswalls]

I was wondering if you would be willing to answer a question that has been brought to my attention regarding water quality applications in a closed loop radiant heating using PEX tubing and a tankless boiler.

Specifically, the discussion has been; what is the best unreactive solution that could be run in the system without potential leaching of platicizers in the PEX tubing and thus wanting a long lifespan of the tubing and boiler without corrosion.

The possible fluids that have been suggested are;

1. Tap water
2. Distilled Water
3. Propylene glycol and tap water
4. Propylene glycol and distilled water
5. Other unknown combinations.
6. DI water
Some have stated that distilled water causes leaching and is not good in PEX tubing. I do not know. I know that tap water has minerals that may build up but to what extent I do not know.

With longevity of the system in mind, may I ask your expert advice on what path I should take or what solutions may be best suited for use in this system?

 

[prodeng]

I can only comment on a couple of those. The distilled water will be a very aggressive water. Distilled is, in fact, acidic (about 5.5 pH). One question I have is whether this will be a heated solution from the boiler or a cooled down water supply to the boiler. That makes a big difference in leaching plasticizers. You may also want to post this in the polymer engineering forum. DI water or demineralized water doesn't have the minerals that would build up in a boiler like tap water would, but I'm not familiar enough with it to know how aggressive it will be in that environment.

 

[bimr]

You should consult the manufacturer of the pex tubing as use of other solutions that you have proposed may void the product warranty. Anyway, here is one link:

http://www.houseneeds.com/shop/plumbing/manuals/vm.pdf

Considering that the tubing has a temperature limit of approximately 140 Deb F, you should not be concerned about dissolved salts depositing out unless your water quality is poor (indicated by high hardness). What you are installing is a closed system, so the dissolved solids are not going to concentrate (from evaporation) and will not be a problem.

There may be some potential freeze protection benefit from using a glycol solution if you are in a cold climate.

I noticed one disclaimer in the link saying the pex system is for potable water. Use of other solutions would therefore void your warranty.