the plastic is Pex....it is the alternative to Copper which is close to 4.00 a lbs..
it is made for heat...used often in todays world..due to the high cost of copper..and labor;)
It is a storage tank.that the Boiler feeds hot water too...
it stores Hot water....
tankless coils are useless ...unless you shower once a week :o
depending on your household.....:confused:
size does matter..