Radiant PEX connections?

iconoclasthero

• Based on the description of my system, I was told I likely have an old/converted gravity system.
  
• The boiler is directly connected to the black iron pipe (BIP) trunk lines with copper. (See photo)
  
• I need to reconnect two radiators so I may have heat for the upcoming season.
  
• The 3/4" BIP connecting lines were removed because the connections need to be relocated up into the joist bay.
  
• There's a total of 8 connections with runs not more than 10 ft. from the trunk lines to the 3/4" BIP pipes going to the upper floors.
  
• I want to use PEX to replace the BIP (especially since I've cut up the BIP to use it elsewhere).
  

1. Is there oxygen-barrier PEX-A compatible with expansion fittings available for sale and if so where? (I.e., I've search for it and can't find it so "yes" isn't a useful answer; I'm looking for a link to purchase.)
   
2. Can oxygen-barrier PEX-Al-PEX be used with regular crimp fittings that I use on potable applications?
   
3. Can oxygen-barrier EVOH PEX be used with regular crimp fittings that I use on potable applications?
   
4. Lowe's offers oxygen-barrier PEX-C. Can this be used with expansion fittings?
   
5. Lowe's offers oxygen-barrier PEX-C. Can this be used with crimp fittings?
   
6. Should brass fittings be used in radiant applications to the exclusion of poly ones?
   
7. I do not have the wherewithal to put a dielectric fitting on the existing connection (see photo) there right now (assuming they make them that big), but do I need them to connect from the BIP lines to brass PEX fittings?
   

Ironman

If you use pex (which is much smaller in diameter than black iron), you may find that you’ll have reduced or no flow to those rads. The system was balanced with the old pipe, but it’s very easy to throw it out by changing pipe sizes.

At the very least, I’d go with 1” or use pex-al-pex which has a similar volume to BI.

You’ll have to use the fittings made for the pipe.

Zman

1. Yes, Uphoner and Rahau make excellent O2 barrier Pex A and expander fittings. They are sold at plumbing supply stores as well as Supplyhouse.com
2. No, Pex-Al-Pex requires special fittings
3. With high-quality fittings, there is no difference between EVOH and potable
4. Pex-C does not work with expansion fittings.
5. Pex-C is made to be crimped.
6. With expander fittings, either will work. I would not recommend crimping Poly fittings
7. You do not need dialectic fitting in a closed heating system. You show good judgment in leaving that one alone.

I would strongly recommend using high-quality Pex-A and connecting with either expander or quality crimp fittings. Lowes is a great place to pick up a broom or shovel. Their Pex is generally a poor quality homeowner grade variety

EBEBRATT-Ed

@iconoclasthero

What @Ironman said.

Unless your reconnect the radiators with the same size pipe your likely to have problems even if the gravity system has been converted to fhw. And if you use more fittings it could be an issue

iconoclasthero

I appreciate the feedback very much and need to review it more closely when I get a moment!

Well, ultimately I want to switch all of this over to under-floor radiant so I can get rid of the radiators all together. The radiator in the bathroom is tiny (22×26×5 in) so the fact that it was fed with the same 3/4 BIP and the gigantic LR radiator (80×26×8 in) leads me to believe that the former should be ok. In terms of the latter, I don't spend much time in that room and would like that radiator to be offline anyway (there's 3 radiators of that size in the LR and DR, and all of them have blankets on them in an attempt to reduce the heat that they radiate and zone it to the upstairs) and I'm not sure I want to invest in the 1" valves I would need to isolate it when I get to putting the under-floor heat in.

What I'm saying is that:

Shouldn't the BR radiator (22×26×5 in) at least be ok with 3/4?

I'm on a pretty limited budget so I was going to isolate these two radiators w/manual FP ball valves but when I was looking for the ones I get from Amazon, I saw this that I could use instead to zone that radiator before I refill the system for the winter.

https://www.amazon.com/ask/questions/Tx2EY9K1C2Y6EIO?sort=helpful

Going from a $5 manual ball valve to a $35 automatic ball valve on one side of the radiator is reasonable but going from that to the Belimo valves 2 orders of magnitude more expensive is out of budget. I don't really care if this is hacked together, I'm not looking to impress anyone.

Zman

When you start modifying a system that was designed for very little flow resistance that used the buoyancy of the hotter water to create flow, you need to be very careful not to add piping or devices that have higher resistance.

If you can find the CV value on that valve, we can speak to the suitability. Have you considered how you will power and control it? It appears to be designed for a boat or some other machinery that uses DC power.

IMO, you are better off paying for quality parts upfront. Those parts are not available at Amazon, Lowes or Home Depot, and they are not going to be the cheapest.

Professionals do not buy quality parts and install things in a workmanlike manner to "impress someone" It is the goal of professionals to give the customer a quality product that will give them a problem-free system that will last for years to come. The "Dead Men" that installed your original system are rolling in their graves at the mere suggestion of what you are considering.

iconoclasthero

Zman said:

The "Dead Men" that installed your original system are rolling in their graves at the mere suggestion of what you are considering.

Lol, they pay for the parts and I'll care what they're doing in their graves.

I don't have the money to pay for quality parts at the moment, I just need this cobbled back together for this season. I guess I'll just get some orange PEX from THD and throw some manual valves on it and call it a day. Do it right another time.

Zman said:

Have you considered how you will power and control it? It appears to be designed for a boat or some other machinery that uses DC power.

AC/DC transformer and a switch. At this point, it's irrelevant. The LR is going to be off, the bath will be on so that is way down the road. Not to mention that there's a manual override.

Ironman

Before you decide to start doing a radiant floor, you need to do a heat loss calc to see if it provide enough heat. A typical radiant floor with quality heat transfer plates can produce about 20 btus per square foot. An older house like yours may need 30+ btus per square foot.