[Greenbuilding] [BULK] Re: PEX tubing

[Chris Green]

Leslie Moyer wrote:
> Lawrence Lile wrote:
>   
>>>>> the expansion and contraction of the pex could crack the slab.
>>>>>           
>>>> Have you actually observed PEX cracking slabs?  
>>>>         
>
> I have no first-hand experience with it, but a friend (who made this 
> mistake) told me that you're supposed to pressurize it prior to pouring 
> the slab, thus preventing the concrete from compressing the PEX and, 
> presumably, also taking care of whatever expansion of the PEX that might 
> occur.
>   

It should also be pressurized before the slab is installed in order to 
check for leaks. It's infinitely easier to replace a run before the 
concrete goes down than afterwards. PEX water lines should also be 
pressurized with air before anything is sealed up. If you pressurize 
either system with air and leave it for a week or two with an air 
pressure gage in place, and the pressure doesn't drop, you know 
everything's tickey-boo and you can call for the concrete delivery.
If you absolutely have to, you can shorten this schedule down to a few 
days, but cautious old me prefers that these systems should really be 
tested for a week or more.

I haven't seen it done anywhere, but it might be a good idea to mark out 
where interior walls will go after the slab is installed so that the 
radiant system installers can avoid placing pipes near the walls.
Having the runs away from the walls will reduce the chance of having 
someone to drill or drive a spike through the tubes. This will allow you 
to pin the walls to the slab. Otherwise you have to glue them in place.
Radiant heat probably should not be run underneath freezers, fridges or 
anything else that doesn't need to be heated (cabinets or wine cellars 
for example.) It's a waste of tubing, etc., as far as I'm concerned.

Cheers,

Chris Green.