# Insulating PEX hot water pipes?



## 1750

I've always insulated my copper hot water pipes in any house I've moved into (though I'm sure woodgeek  will burst my bubble and tell me that this is a green myth as well....).  My new house has PEX tubing, which seems (to the touch) to transfer much less heat through the pipe wall -- which I'm equating with reduced heat loss.  

Do folks think it still makes sense to insulate PEX piping? 

Thanks.


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## starfoxACEFOX

PEX pipe only as R-value of about 0.06. Which not very big from copper pipe. Some building codes require PEX be insulated just as copper would. To meet codes R-value of 2 to 5


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## woodgeek

Seems like a good idea, esp if you DHW is more expensive per BTU than your space heat, which is usually the case.  It would also lead users to save some water (by pouring less down the drain waiting for warmup).


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## 1750

starfoxACEFOX said:


> PEX pipe only as R-value of about 0.06. Which not very big from copper pipe. Some building codes require PEX be insulated just as copper would. To meet codes R-value of 2 to 5


Wow, that's surprising and good to know.  Thanks!  I wish I would have asked this before we drywalled the basement ceiling.   I will get at the exposed stuff, however.



woodgeek said:


> Seems like a good idea, esp if you DHW is more expensive per BTU than your space heat, which is usually the case.  It would also lead users to save some water (by pouring less down the drain waiting for warmup).



I put a Rinnai tankless system in, but the propane to heat the water is like compressed gold.   Definitely more expensive than the wood I use to heat the space.

Thanks to you both.


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## semipro

I'm installing PEX currently and plan to insulate both hot and cold lines.
The hot to save energy.
The cold to prevent condensation and potential mold growth.  (I've seen it happen on uninsulated copper pipes above drywall ceilings)
An added bonus of the insulation is that it provides a barrier preventing damage from rodents and light.
Mice have been know to chew on PEX and PEX is susceptible to decay from light.


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## maple1

I'm having a hard time accepting that Pex has similar R-values to copper. I know I have to run water for a little while to feel heat on the outside of a Pex pipe compared to copper - copper is almost instant.

That said, I'd likely insulate, and did. Both hot & cold.


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## Highbeam

I insulate the hot and cold pex in places where it might freeze only.

I do not believe heat transfer through the thick plastic pex is nearly as good as with copper pipe. Copper is used in lots of places for heat transfer like baseboard radiators. I expect that if plastic could have been used it would have been to save cost.

Another place people use copper is in compressed air lines. A reason is the heat transfer to cool the compresed air. When you want to use pex for compressed air, one of the biggest arguments is that the pex won't allow enough heat transfer.


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## woodgeek

Hey, I think Foxler was just saying that the R-value of the pipe wall was negligible in both cases...it is a very small number in one case, and an even smaller number in the other case.
I agree.


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## EatenByLimestone

IME, it doesn't transfer as well as copper, but I can assure you that it does transfer.  Mine is insulated with the black foam at the very least.  Some also has fiberglass over the top of that.


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## Highbeam

woodgeek said:


> Hey, I think Foxler was just saying that the R-value of the pipe wall was negligible in both cases...it is a very small number in one case, and an even smaller number in the other case.


 
True, it's not as though the plastic wall is a substitute for actual insulation. Half of zero is still zero. 

Supposedly, I haven't tried, but you can freeze water in pex and it won't burst. Fittings may burst but on a straight run.....


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## 1750

Highbeam said:


> True, it's not as though the plastic wall is a substitute for actual insulation. Half of zero is still zero.
> 
> Supposedly, I haven't tried, but you can freeze water in pex and it won't burst. Fittings may burst but on a straight run.....


The electrician forgot to turn the furnace breaker back on and I had a pex line freeze up last week.   But, thankfully it seemed to come through without incident.

The line is on an exterior wall and some monkey tucked it IN BACK of the insulation!   I'm going to try and slide some pipe insulation onto it pronto.


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## starfoxACEFOX

1750 said:


> Wow, that's surprising and good to know.  Thanks!  I wish I would have asked this before we drywalled the basement ceiling.   I will get at the exposed stuff, however.
> 
> 
> 
> I put a Rinnai tankless system in, but the propane to heat the water is like compressed gold.   Definitely more expensive than the wood I use to heat the space.
> 
> Thanks to you both.



No problem


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## Bret Chase

Highbeam said:


> True, it's not as though the plastic wall is a substitute for actual insulation. Half of zero is still zero.
> 
> Supposedly, I haven't tried, but you can freeze water in pex and it won't burst. Fittings may burst but on a straight run.....



I have learned that PEX will freeze far faster than copper... My entire potable water supply from the pump up has been replaced in the last 3 years.... from a mishmash of galvanized pipe, copper pipe and copper tubing.  since I replaced the last runs of 5/8 copper tubing to my kitchen sink..... it has been a nightmare when it comes to freezing... and completely randomized at that.  With the UNINSULATED copper tubing... the kitchen lines NEVER froze.... seriously... EVER. with the heavily insulated PEX... it freezes at random times.... it will flow hot and cold just fine at -5F... but freeze up at +20.... and this morning it was froze up tighter than a teddy bear when the night spent most of it's time south of -10F.  On the pex i've got armaflex on the pipe... and where it passes between the floor and the bottom of the cabinet.... 4" of solid poly-iso... 6" in all directions... and then spray foamed to seal everything else.  still freezes.

I love the ease of PEX installation.... but this freezing behavior makes NO sense at all...

and yes, pex survives freezing just fine... with both brass and poly fittings.


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## woodgeek

Bret, could the freezing be driven by wind conditions?  Could a length of the pex be near a crack/air infiltration area that gets a draft when the wind blows from the right direction, but not otherwise?  The ability of a copper pipe to conduct heat along its length might have prevented a short section from freezing is adjacent areas were above freezing....with pex not so much?


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## Highbeam

woodgeek said:


> Bret, could the freezing be driven by wind conditions?  Could a length of the pex be near a crack/air infiltration area that gets a draft when the wind blows from the right direction, but not otherwise?  The ability of a copper pipe to conduct heat along its length might have prevented a short section from freezing is adjacent areas were above freezing....with pex not so much?


 
When I worked on submarines, we used to freeze plug pipes so that we could make a repair. One really cold spot on each side.

The coppers superior conductivity could have allowed it to wick heat from elsewhere on the pipe to prevent freeze up.

Good to know that the pex fittings are able to freeze too.


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## Bret Chase

woodgeek said:


> Bret, could the freezing be driven by wind conditions?  Could a length of the pex be near a crack/air infiltration area that gets a draft when the wind blows from the right direction, but not otherwise?  The ability of a copper pipe to conduct heat along its length might have prevented a short section from freezing is adjacent areas were above freezing....with pex not so much?



my house was built in 1865.... EVERYTHING is an infiltration area.  I added some more polyiso insulation against the rim and under the kitchen floor yesterday.  when it warms up I will sprayfoam it tight...


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