This is a hydronic heating application question.
I am gut-remodeling a 1920's 2-story. I want to save the cast iron radiators. I ran PEX for the heating runs to each radiator but don't want to come through the floor with PEX.
So, my question is (since I think there is a risk of corrosion between brass and cast iron), is there a fitting that is cast iron for a PEX crimp connection? I can't seem to find one anywhere.
Of course I could use brass (crimp PEX to Female NPT) to connect PEX to cast iron but I don't really want to buy 24 dielectric unions (12 radiators). Also, I really don't want a union inside of my wall or under the floor.
Does anyone have a solution or experience with a similar problem?
Thanks!

Hi Jkorver...

You know, in over 30 years of plumbing and heating work I very rarely use dielectric fittings. I'll use them on large commercial applications, but almost never use them residentially. I install all kinds of forced water systems and all kinds of steam systems and very rarely have ever had any issues at the junction with the dissimilar metals.

If you have SOFTor BASIC/NEUTRAL water I'd recommend that you use the all brass MALE x PEX adapters and use plenty of teflon tape at the threads... say 7-8 wraps and then change over to PEX. I can pretty much promise you that you will be just fine for decades to come.

If, however, you have extremely HARD WATER in your area, then it may be a good idea to consider the dielectric unions just to be on the safe side. Hard water and dissimilar metals can create problems over the long run.

Glad to discuss more...

Mark

[If, however, you have extremely HARD WATER in your area, then it may be a good idea to consider the dielectric unions just to be on the safe side. Hard water and dissimilar metals can create problems over the long run.]

Thanks for the info Mark. I am not sure if I quoted properly (my first time using this site).

Anyway, pertaining to above, do you think propylene glycol will adversely affect this also or create problems? I don't think it would have any affect on whether the water is harder or softer, but I wander if it would speed up the electrolysis process. I plan to add propylene glycol to my new system (closed system).

Most Propylene glycol mixes have a non-corrosive additive added to the mix that should help reduce the corrosion to the pipes and the entire boiler system for that matter. In my opinion, and with 100s of boilers under my belt, you should be just fine without the dielectric unions... ;)

To be fair, however, give some of the other individuals/experts online to chime in on this... always best to get all sides to a story so you can make the most informed decision possible!

Mark

PEX crimp fittings are not a good choice for water over 130 degrees. I have seen PEX used in hydronic heating, I did it myself once because it was the only reasonable way to do the job, but I used $pecial compre$$ion fitting$. I have heard of it being done, but would not trust crimp connections in a 180 degree hot water heat system in my own house. I'm not even certain I would want to crimp hidden connections on a 120 degree water radiant floor system in my own house.

The brass to cast iron will not be a problem if installed correctly on recirculating water. Especially with a glycol additive.

Hi Epmiller...

Nice to see you posting again... been awhile!

If you are talking about regular PEX tubing then I'd agree that you shouldn't use it on heat because there is a better PEX choice for heat and that is the oxygen-barrier PEX they sell specifically for heat piping

Pex crimp fittings and oxygen-barrier PEX are absolutley no issue in hydronic heating systems. You don't want to hook O2-barrier PEX directly to anything that is a heating source such as a water heater or a boiler... must stay a minimum of 24" off these appliances, but after 24" O2-barrier PEX is perfectly fine.

It's pretty great stuff and pretty much all we have been using on heat systems for over 10 years now and you know, when the proper oxygen barrier PEX is used with hydronic heat systems, there has been absoultely no corrosion seen and the crimped fittings are perfect... ;)

Let me know what you think, OK?

Mark