Effect of 1/2" PEX Section on Baseboard Loop

Brent H.

Greetings,



My parents have a ranch house with forced hot wated baseboard heat. Recently, a contractor accidently put a couple finish nails through a piece of 3/4" copper pipe in the basement used to connect sections of baseboard located on the first floor. The had a plumbing contractor come out and replace the pipe and I noticed they replaced about 10' of 3/4" copper with 1/2" PEX(I assume oxygen barrier). Will the restriction caused by the 1/2" PEX cause any problems?



Thank.



-Brent

kcopp

depends...

how many feet of baseboard are on that loop? Are you sure its not 5/8" pex?

icesailor

PEX replacements:

A good question to ask. IMO, it never should have needed to be asked. Does the installer who replaced the damaged tube have a torch or know how to solder? I can not believe that anyone who calls themselves  a heating professional would do anything as stupid as that. And run the risk of someone posting such foolishness on a board such as this. You should post it on HVAC-Talk.com on the Wall of Shame.  The very fact that someone may not know that maybe it is OK because of the load on the circuit, doesn't mean your reputation will be destroyed by the unknown.

In other words, it may work. OK mostly. If it doesn't "mostly", it needs to be changed. And a few feet of copper tube with a couple of repair couplings (no stops) would have been easier and quicker than dragging all that PEX stuff out.

Simply amazing. Like the fin tube installed 90 degrees off. Simply stunning at the incompetence of others.

kcopp

but Ice...

stuff like this keeps us in business...

MIke_Jonas

I disagree..

Stuff like that makes people hate radiant heat and put in forced error.

STEVEusaPA

responding to KC, and Ice.....

Yeah it keeps us busy, but it aggravates the youknowwhat out of me.  People can make money even if they're a hackasaures.  I blame it on something I've noticed starting about 15 years ago--the Home Depot Effect.

Before (and still now, for me), a contractor had to go to a supply house, have an account, build a relationship, learn their trade through time/education/experience, etc., to be in business.  But now, anyone with a van and a HD charge is a 'contractor'.  No regs for them...no sense of pride or professionalism.  Just hack away and cash a check.

Thats why I do everything possible to avoid tools, and especially parts, from a company that lets a big box store sell anything to a customer, with no regard of the consequences. Yes....I'll go there in a pinch, or a Sunday, then get mad at myself for my poor planning.

In my area (Philly suburbs) there are plenty of supply houses to support, and I always go there first.

Sorry about the hijack, and the rant.

Brent H.

Pex Size

When I get a minute I'll double check.... maybe it is 5/8" PEX? It certainly isn't 3/4" but never thought about the possibility of 5/8".

SWEI

PEX size

Inside versus outside diameters.  Either one will work, just have to be clear what you are measuring.

Brent H.

OD is .750"

I used a pair of calipers and the pipe has an OD of .750" which I believe is 5/8" PEX.

The 5/8" section is about 7' long and the loop contains approx. 85' of baseboard.



Thanks.

Mark Eatherton

Not good...

The 5/8" will create a restriction for sure, but more importantly, your loop is pushing the limits for how far a loop should/could be. So long as the baseboards at the end are substantially longer than the ones at the beginning, it might not be an issue. As the water flows through the circuit, it gets cooler and cooler, eventually running out of useable hot water. By my estimate, you'd need to be flowing around 4.6 GPM, which puts you over the top for 3/4" copper pipe as it is anyway. The one thing you have going in your favor, is that the real time load is probably half of what you think it is, so it will work OK, but I would expect to hear a hissing noise where the 5/8 PEX is due to restrictive fittings and excess velocity.



What the 5/8" is NOT doing, is causing the whole loop to think that 5/8" is the pipe size throughout. It is just a choke spot in the road of life... I think a lot of people see that 5/8" and think to themselves that that is what the pump thinks the whole system is piped in. Not so. Just a short pinch point, but still not conducive to as good a flow as it could be.



ME

Brent H.

Long Loop

Mark,



Thanks for the info. I've always suspected the loop was too long but never did the math. The bedrooms at the far end of the loop are generally cooler than the other rooms on the loop. Of course, it's been this way for at least 35 years so I think my folks are used to it If it matters, I think there is a standard 007 pumping it.



Is the section of 5/8" PEX going to make it noticably worse?



Thanks.

icesailor

.75" OD:

If the OD is .75" or 3/4" OD, it is closer to .50" or 1/2" ID than 5/8" ID. The wall thickness of PEX is thicker than copper and 3/4" OD copper is considered 5/8" ID. PEX would be smaller.

Mark Eatherton

It isn't gong to help...

To be honest, the problem in a LOT of cases is that there is a shortage of good, trained service technicians. Not just in plumbing, but in EVERY category. So the service companies have resorted to hiring salespeople, and teaching them to plumb. PEX, CSST and many other low tech piping systems that require little to no skill levels ends up being the path of least resistance. The fact that the tube used was undersized is inexcusable. They need to come back and change it to either copper, or 3/4" oxygen barrier PEX.



Honestly, with a loop at this length, short of completely replumbing the circuit, there is not a lot that can be done that would make it much better You could put a 4 way reversing valve on that circuit that would change the water flow direction every 5 minutes or so. Or you might be able to install non electric thermostatic bypasses on every piece of board, and as rooms warm up, the flow would bypass that board and go to the next one.



I have Siggys sizing software, and if you can provide a room by room heat loss, I can run his software that would tell you how much board is needed for each room. I'd need to know what room gets flow first, second and so on.



When properly done, the board starts small at the beginning and gets longer as it goes through the circuit, for obvious reasons. The software also allows me to select different pumps to see what the flow rate will be (approximately). You need right at 4 GPM to deliver the goods at design condition.



ME



ME