Replacing HW Iron Pipe with PEX: Good Idea?


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Old 07-12-06, 07:12 PM
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Replacing HW Iron Pipe with PEX: Good Idea?

I'm living on one side of a duplex while renovating the other. The plan is to convert the home into a single dwelling. The "old" side of the house used a coal furnace and convection air (no fan!) for heating. All that has since been removed and a heating system is required on that side.

On my side of the house I'm considering changing out the iron pipe with PEX. The biggest reasons are:
1) there are no zones at all and upstairs heating in the winter is horrible. The current piping arrangement does not lend itself easily to cutting in for zone installation.
2) since I want to use hot water radiators on the renovated side as well, PEX would be easiest to install and would cut down on the heated volume of water.

Does changing out the iron pipe with PEX make sense?

With regard to point #2, if I do use PEX and do reduce the water volume of the system, will that reduce the overall efficiency of heat transfer to the cast iron radiators? i.e. can a smaller volume of water get enough heat to the rads?
 
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Old 07-13-06, 02:05 PM
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Pex

PEX is ok for in or under floor radiant heat but I don't know that I would use it for cast iron radiators. With the vast heat expansion of PEX at the temperatures at which you would be operating for the cast iron, it would be a sloppy looking mess at best. Steel pipe is my first choice with copper coming in second.
 
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Old 07-13-06, 07:22 PM
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PEX vs Steel

Hi Grady, thanks for the reply. The "boiler" is actually a hot water heater and is a combination unit that heats the domestic water as well. The temperature of the water is set (I believe, I'd have to run downstairs and check) to a maximum of 170F and with two small children I've lowered the water temperture below even that.

Around here, people with hot water baseboard convection heaters use the exact same heater that I'm using. My father and friend both have the same hot water heater and both use PEX tubing to connect it all together.

My basement is ~ 40 x 30 and is basically unused so there is lots of space. I have seen pictures of complicated PEX piping and I have to admit, it does look like a dog's breakfast.

My thought was to run a large PEX main around the basement and take smaller feeders off of it. Same for the return line back to the heater. Of course, I would need the appropriate flow control gear to try and balance the whole thing.

Does the lower temperature and examples I cited make you re-think what you've said? I'd basically have to repipe the whole basement in steel and while intimately aquainted with a pipe threader I also know how much work all that threading can be.

Rob
 

Last edited by RHamper; 09-24-06 at 11:56 AM.
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Old 07-13-06, 09:23 PM
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Why do you intend to use a feed tube ("main") with many runners conncected? Wouldn't it be easier just to have a straight run of PEX from a manifold to each of the boilers? The manifold would be a little extra cost, but it would allow you to shut down heat to any radiator at the source. What have your neighbors done?
 
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Old 07-14-06, 08:31 AM
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RE: Manifold

Why do you intend to use a feed tube ("main") with many runners conncected?

Good question. Short answer, I'm not a plumbing expert.

Long answer: I'm concerned about volume flow and pressure drops when two or more zone valves open. I was looking at the steel pipe layout that is fitted and it, of course, has progressively narrower piping as radiators are tied in. I was basically copying that system (as well as that from some hydronic heating sites). Also, I figured that maybe the installation would be neater if I just had one large main running around the basement instead of lots of PEX tubing. Hmmm, then I'd have a large dead leg with cold water which would kind of the defeat the purpose of cutting down on water volume, right?

What have your neighbors done?

Now my dad's system is pretty much PEX from the the zone control solenoids that are fitted to the copper manifold at the boiler. BUT he uses the baseboard convection heaters which require far less water to work properly than my cast iron radiators.

My friend uses a similar layout as dad but he does have cast iron radiators. Apparently the downstairs heating is great, but the upstairs heating is not so good. However, that could be the way he has the system balanced as opposed to the use of PEX to supply the radiators.

I'm sorry guys, I don't think I've outlined the situation very well. It's a big job with lots of considerations and it's hard to get all the info into a discussion group. I'll try again.

I believe my main from the boiler is something like 2". Come to think of it though, the outlet from the boiler is perhaps just 1" and.... Just went down and checked: 1 1/2" at the boiler, reduced to 1" (I can only presume it was to fit the non-return/safety valve) then it goes to 1" copper (with a 3/4" tap for one radiator) and the subdivides to one 2" iron header and one 1 1/2" iron header.

So here is where my problems start. I want to zone the upstairs of the side we're currently living on, but some radiators are on the 1 1/2" header and the others are on the 2" header. In order to zone I'd need two solenoids of quite large size. A plumber said I'd likely need another pump too though I'm not sure why.

Further, I will want to zone upstairs and downstairs of the opposite duplex side (giving 4 zones in all minimum). To do so, I'd have to cut into either the 2" or 1 1/2" header or both.

So, to me, it seemed to make sense to rip all the iron pipe out and start over from scratch. PEX would make the new installation easier to work with.

The other design criteria was that we wanted to keep cast iron radiators in the house. It's an old house and the CI rads would be in keeping with the character. I have toyed with the idea of CI rads just downstairs with baseboard convection heaters upstairs. I assumed this would be more economical as less volume of water had to be heated.

Everyone I talked to has advised keeping the CI radiators. I'd love to keep the cast iron radiators and in fact I'd have to buy more as the other side has no radiators at all. My concern has been that the PEX would not be able to supply an adequate amount of water to make the CI radiators worthwhile. As I noted, the water temperature is fairly low for such radiators (in the meantime, they do get too hot to touch and do heat several rooms quite nicely).

So, several questions have arisen:
1)Is keeping the cast iron radiators a good idea?
2)If not, can I at least keep the downstairs rads?
3)If the CI rads are OK (or I can live with decreased efficiency), can they be suppied adequately with PEX piping?
4)Should I replace all the steel manifolds with PEX while I'm at it?
5)One thing, I saw my friend's PEX/CI Radiator setup and the PEX is UGLY where it connects to the rad. I may just keep the "leader" piping up to the rads as at least the steel pipe looks neater running up the wall.

Thanks for your patience and input.

Rob
 
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Old 07-14-06, 02:27 PM
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Piping

At this point we don't know if your system is mono-flow or series loop. If there is one pipe which comes off the boiler & runs around the perimeter of the basement with a bunch of tees on it leading to the radiators, you probably have a mono-flow (diverter tee) system. Some pics of the piping would help.
You can keep the cast iron rads but don't mix radiators & baseboard on the same loop.
 
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Old 07-17-06, 08:58 PM
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Replacing Iron with Pex

Rob:
Your situation is pretty close to mine, so I'm eager to learn what the gurus here have to offer. I have an old monoflow system that heats the basement and two stories upstairs. There are some recent additions to the house ("recent" being a relative term) that are heated with electric. I'd like to do a separate zone for those rooms and use radiant floor heating. The would require a mixer and separate pump, I assume, but not insurmountaible.

I'd also like to get rid of the pipes running just below the celing in the basement -- ugly and low in small (but liveable) rooms. So here's my mad scheme:

1) run two more lines out (and in) to the boiler. One line would feed the lower temp floor radiant rooms. The other would feed a manifold.

2) Do straight runs to each of the radiators, or loops for up to three radiators that can be served by that single line. This is determined by the direction of the floor joists -- I really don't want to tear ceilings out (they're plaster over cement over fiberboard of some sort). My radiators are stainless or aluminum fin type radiators, not the cool old cast iron radiators.

Since this is a job I'll be doing alone or, god help me, with the help of my 14 year old, I don't anticipate making quick progress. So my plan was simply to plug the main pipes as their feeders were cut off and replaced with pex.

Then, I will muster my troops and head to Waterloo. Unless someone saves me first by explaining why this is all wrong and won't work. Criticism appreciated; suggestions remembered and treasured.

Mark
 
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Old 07-18-06, 04:38 PM
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Mark & Rob

I have absolutely no problem with PEX for a radiant loop. In fact I would use nothing else. My only problem with PEX comes in to play with the high temperatures for baseboard, cast iron rads, convectors, & hydro-air. The temperatures in these applications lead to dramatic expansion & contraction of the PEX. With all of this going on & in addition to the "explosion in a spaghetti factory" look I can't help but think it has to be tough on the tubing eventually leading to leaks.
Mark: If your "radiators" are actually convectors, as opposed to baseboard, I suggest staying with the mono-flow configuration. Even though convectors don't hold all that much water, there is a significant temperature drop thru them. A mono-flo configuration helps for each unit downstream of the first.
 
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Old 07-18-06, 07:07 PM
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My System

Originally Posted by Grady
At this point we don't know if your system is mono-flow or series loop. If there is one pipe which comes off the boiler & runs around the perimeter of the basement with a bunch of tees on it leading to the radiators, you probably have a mono-flow (diverter tee) system. Some pics of the piping would help.
Grady, thanks for your patience. I took pics and then found that I couldn't upload here. I do have some private webspace, but I'm out of time to do much more as I'm off to sea tomorrow (have to find and install FTP software, figure out the access for the webspace etc). Would it be ok to pick up this thread again when I come back in about four weeks?

As to my system. It's not exactly a perimeter loop. It's more like two manifolds: one of 1 1/2" and the other of 2" (going left and right from the boiler). There are tees in the line, but they look like ordinary tees to me. However, after each tee, the main line reduces by one pipe size so I would guess that the back-pressure is there to drive it to the rads if need be.

The returns are all connected in a similar fashion. i.e. they come down and join two separate return mains and then back to the boiler.

I read somewhere that PEX is good up to about 200F. As I noted, my system is water is less than 170F. Is this still a concern for PEX?

Thanks and regards, Rob
 
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Old 07-18-06, 09:48 PM
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Pex Loops

Thanks, Grady. But I had to think about what you said: "A mono-flo configuration helps for each unit downstream of the first." As I understand that, the monoflow has the advantage of supplying each convector with water of the same temperature, while in a loop the last convector served might get lukewarm water at best.

But if each convector was fed directly from the manifold, or if there were no more than, say, 2 convectors on a loop, wouldn't that be as effective as the monoflow?

Like I told my attorney: seemed like a good idea at the time.

Mark
 
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Old 07-19-06, 05:27 PM
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Certainly, you are most welcome to pick up where we leave off. If you can find the original posting, please continue this one. It makes it a lot easier for us old folk, lol.
You can host pics on photobucket or any similar photo hosting site & just provide a link here.
I am not as concerned about the temperature tolerance of the PEX as I am the flexing & it's long term effect.
An easy way to tell if your system is mono-flo is if there are two tees going to each convector. If so, most likely it is mono-flo. Also look closely at each tee to see if there is an arrow on it. If you find an arrow indicating direction of flow, it is certainly a mono-flo tee. Only one of each pair of tees would be a mono-flo tee in the vast majority of cases.
Do you have separate return piping? If you do, it is not mono-flo. Mono-flo systems use the same pipe in a big loop for supply & return. They just have tees.
Have a good voyage & stay safe out there. The sea can be a great place or she can be nasty.
 
 

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