Serious Shrinkage

[McKraut]

I run my boiler at 175*. I use a heat exchanger to transfer the boiler heat two 40 gallon buffer tanks. As the water leaves the buffer tanks, it goes through a temperature mixing valve making the water going to the house 120*. I have a continuous loop that supplies hot water and tap off the loop for heating and DHW. My run of Pex from the boiler room to the house is 100 feet each way. I notice when I start the system up in fall the Pex creeps in length at least 1 inch where it leaves the boiler room and where it enter the house. When the system is shut down the Pex returns to it original length. I think Pex is only rated at maximum 180*. Are you sure you are not over heating the Pex and it now will not return to it original length.

I am no expert on PEX but my understanding is that it is acceptable to have it go to 200°. Beyond that, it can be problematic. I run my boiler at 180° and have my aquastat set to kick on the overheat loop at 195°. I am sure there are others here that can give you the exact information. I have a 100" underground run and the PEX has contracted and expanded approx. 1&1/2 inches on both ends.

Bob