Best PEX for cast iron radiator

JerseyJon

I'm moving a cast iron radiator. The old one was A) cracked and at the bottom of the staircase where it would have sent its heat upstairs if I hadn't disconnected it. I'm putting the new one across the room, (first floor) under a window using the existing 1-inch fittings in the main supply and return pipes. I'm hoping to run PEX the 12 feet across the basement ceiling to the new risers. I've figured out that I need aluminum with an oxygen barrier. Are all brands equal if the specs are the same? And what about the fittings? I don't want to buy a $300 tool for one radiator. But I want to do it right. I can borrow a crimping tool for the copper sleeves, so that's within my budget if that's a good option. Suggestions? Thanks.

JStar

I'm hoping that this is a hot-water heating system...?

JerseyJon

Yes. Sorry forgot that detail. Hot water.

JStar

Then, yes, most any oxygen-barrier PEX will be fine. How many BTUH's is the radiator?

JerseyJon

Thanks Joe. So the crimped copper sleeves are OK?
I would have to go back and look up the BTUs. I crunched the numbers in the spring and then spent forever looking for the size and style I wanted, then weeks stripping and painting them. So I've forgotten where I started. Maybe it was the paint fumes. What's the significance of BTUs and PEX? The replacement radiator is slightly higher BTUs than the unit it's replacing.

JerseyJon

I calculated it at about 8,000 btus. Supposedly there's an impressive list here of radiator btu ratings.

JStar

Moving 8 GPM will achieve 80,000 BTUH's at a 20F Delta-T, you'll be fine with 1" PEX. Just like to confirm; might have been able to use a smaller size to save parts cost.

EDITED POST.

Zman

@jstar
I think you misplaced decimal. 8 GPM is 80,000 but at delta 20
Sounds like an old gravity system so sticking with the big pipe is not a bad idea.
Carl

JStar

Zman said:

@jstar
I think you misplaced decimal. 8 GPM is 80,000 but at delta 20
Sounds like an old gravity system so sticking with the big pipe is not a bad idea.
Carl

You're right! So, even a run of 1/2" PEX would work. I was on the right track. Math is too hard at the end of the day.

icesailor

"" You're right! So, even a run of 1/2" PEX would work. I was on the right track. Math is too hard at the end of the day. ""

Split the difference and run 3/4". You won't go wrong if it is a now pumped gravity system.

IMO, you'd be wide to drop through the floor from the radiator with copper and switch to PEX under the floor with straight lengths.

Personally, I'd run Type M copper and be done with it. A lot easier to hang. And you can spend more on a night out dinner and adult beverages than you will save by going to PEX with the cost of all the adapter fittings and running around borrowing tools.

JerseyJon

It is indeed a converted gravity feed, now pumped. Icesailor, you may be right. I have most or all of the fittings to do it with threaded pipe so that might be about the same cost.

SWEI

Keep the pipes at 1" if at all possible. Even after adding a pump, system balance (relative flow rates) will be thrown off by a small diameter replacement.

j a_2

Can you post a pic. Are you sure its a gravity system, converted?

icesailor

SWEI said:

Keep the pipes at 1" if at all possible. Even after adding a pump, system balance (relative flow rates) will be thrown off by a small diameter replacement.

I would have suggested the 1" also but I always fear the mining pump crowd starting another war.

How much resistance in feet of head pressure is 24' of 1/2" PEX equal to?

So, if there is very little resistance/head to the rest of the radiators in the system, because water DOES care where it goes, and always seeks the path of least resistance, will you get the desired flow to the moved radiator with the 1/2" PEX as opposed to all the other ones that are 1" or 1 1/2"?

I know that I have found converted Gravity systems where someone added a radiator and ran a long length (60+' round trip) that didn't work well at all.

j a_2

Can u posta pic. of the boilers near boiler piping…just curious what someone may have done here

JerseyJon

Here's a pic near the boiler where the copper connects to steel
And another towards the end of the run after a couple of steps down