Home>Discussions>PLUMBING>Problems with pex pipes and baseboard heat
8 posts / 0 new
Last post
1Rick
Problems with pex pipes and baseboard heat
1Rick

I recently had some baseboard heat pipes replaced in my house during a renovation. The baseboard system was previously all copper pipes. In the renovation the contractor used pex pipe for the return lines in place of copper. The baseboard heat elements (with fins ) is still copper. The returns run under the heating elements.
Now when the heat comes on the pex pipes expand and pop out from the baseboard heat covers by as much as 6 -9 inches from the baseboard covers in a 10-15 foot section of the system. It is clear that the pex pipe has a much greater thermal expansion than copper pipes when heated. In an attempt to resolve this, the contractor has used some form of clips to restrain the pex pipes from popping out.
The thermal expansion is obviously still taking place and while the clips keep the pex pipes within the baseboard covers, I am concerned that the expansion and contraction will cause the pex fastening connections to loosen over time and we'll have a leak; or the plastic pipes rubbing against other parts of the baseboard when it expands and contracts with cause wear and result in a leak

Is this thermal expansion a common problem with pex pipes used in baseboard heating systems ?

Does anyone have experience with the use of pex pipes and baseboard heat ?
Thanks

dj1
Re: Problems with pex pipes and baseboard heat
dj1

You got PEX, you got what you paid for. I would have insisted on copper.

PEX can withstand the heat, I think it's rated for up to 200 F, but the big question is: can the connectors and connections take the pressure? Is the workmanship something that can be trusted?

1Rick
Re: Problems with pex pipes and baseboard heat
1Rick

That's the worse part, the plumber sub contractor did not seem competent

dodsworth
Re: Problems with pex pipes and baseboard heat
dodsworth

1Rick,

Yes, I agree--the plumber sub-contractor didn't seem to do the competent thing in this retrofit situation; and yes, I agree that PEX thermal expansion is more than the same length of copper tubing, but copper tubing expands as well, & can be more likely to stress the copper joints, especially as they enter the nearby flooring---standard practice is to consider the outer baseboard steel housing, aluminum fins, & adjacent supply/return copper tubing as part of the HEATING CONVECTOR, where all these metal parts will expand/contract at about the same rate during their heat/cool cycle.

I wonder if you could provide us with more info as to exactly why the baseboard returns needed replacement in the first place--this is quite a rare occurrence unless there was a situation where the copper return pipes froze during a cold snap, or the baseboard supply/return copper loops were being retrofitted & separated into zones, for example, or some other reason????

In the event it was just one copper tubing baseboard return that needed a changeout, the ordinary procedure is to replace the damaged copper return with another relatively short copper return that is installed under the fin-tube element UNTIL YOU REACH THE POINT WHERE THE SUPPLY/RETURN PIPING DISAPPEARS into the walls or under the flooring on its way back to the mains or back to the boiler.

Once the baseboard supply/return piping goes inside the walls, it then becomes an issue as to whether the repair/renovation job is accessible to the plumber doing the work---if this is a one-story home with a full cellar, where the return lines are accessible, then the homeowner is given the choice of having copper tubing installed at a much higher price than PEX, or the option of having PEX installed at a fraction of the cost of copper.

Then there are the very common situations where the plumber has NO ACCESS to the supply/return piping---they're all deep inside the walls of the house---so the choice is to rip out the plaster, sub-flooring, 2X4s, etc. until a big-enough hole is made to re-install copper tubing---in such cases, flexible PEX tubing is a God-send for this particular situation, since it is flexible enough to be threaded thru sub-flooring & wall cavities without tearing half the house apart to do it (think of an electrician snaking a thin-wire metal snake thru the walls to run a new piece of romex thru a wall)---again, the homeowner should be advised of the price differential that will be incurred between a very high copper tubing install & a much lower cost PEX install.

In the case of the baseboard element, the LABOR COST between installing a short piece of PEX and a short piece of copper tubing is about the same---the COST PER FT. of the copper tubing, however, is more---so it's only good installation practice to advise the homeowner of the rather modest cost difference & let the homeowner decide.

MLB Construction
Re: Problems with pex pipes and baseboard heat
MLB Construction

i'm not a plumber so maybe our plumbing experts can confirm this. i believe, that when using pex piping for heat, it's supposed to be Fosta Pex pipe (if i have the spelling correct). This version of pex piping clad in an aluminum sheathing and that aluminum sheathing is clad in another material. it's essentially a 3 layer thick pex pipe designed for baseboard heating. regular water supply pex is designed to take temperatures up to, i believe, 120 degrees which is as hot as a water heater can allow to run to your fixtures. The water that runs through baseboard heaters can be as hot as 180 degrees. Hence the reason for different Pex pipes for different situations. easiest way to tell is to look at your pex piping that he used for the returns, if it's red, blue, white or black then it's the wrong kind. if it's a light grey color, then he used the correct one.

and again, hopefully JohnH2O or another plumber can confirm if i'm correct or not.

Condoman
Re: Problems with pex pipes and baseboard heat
Condoman

I am not a plumber either. I have worked with PEX and copper and PEX is just fine for hydronic heat applications as long as it is the oxygen barrier type. I plumbed my addition in 2012 with OB PEX using SS crimp rings. I ran a 40 PSI pressure test before having the under side of the framing closed.

When we bought the house all the plumbing including radiators had been replaced with PEX. The only leak I had I created myself sweating a fitting on the end of a baseboard run.

When our boiler cycles for heat we hear creaking as the PEX and wall units expand. To me it is like music indicating the job is being done.

1Rick
Re: Problems with pex pipes and baseboard heat
1Rick

I should have explained the situation in more detail.
We had a fire in our house in Jan 2013 and without heat in the house the baseboard heating system had a number pipes burst from trapped frozen water. Most of the heating elements survived and those that didn't were replced with copper, Pex was used only for the return pipes that had to be replaced. So we have copper heating elements taking flow in one direction and pex pipes bringing it back through the same baseboard enclosures.
The pex pipes that was used seem to be right type that is recommended for heating systems. Despite using the right type of pipe, the problem is when the heated water is running through the system, the pex pipes expands and flexes out of the baseboard enclosures, but then shrink back to original length once the heat dissipates.
I am surprised by the extent of the expansion and concerned that restraining the pipes with fastening clips will lead to problems down the road. The clips restrain the pex pipes from popping out of the enclosures, but the pipe is still expanding just as much and the stress is being transferred , not alleviated. I am not sure what the solution is for this, and was hoping others had experience with similar situations and could offer some advice on options.
Thanks

Daniel
Re: Problems with pex pipes and baseboard heat
Daniel

There are four main categories of PEX. Oxygen Barrier Pex is used to reduce expansion and reduce oxygen into a system preventing deterioration of downstream cast iron boiler and boiler trim. In your case, I suspect PEX A (non oxygen barrier) was used. A remedy is easily had. Deinstall incorrect PEX and Install Oxygen Barrier Pex. 

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.