Pex Waterline used to plumb the boiler into water system. All water must be transported from the boiler, to the heat exchanger being used. Please note, insulated PEX tubing is used when plumbing water outdoors where the temperatures are subject to freeze. Oxygen Barrier PEX tubing is required on Closed-Loop hydronic, radiant in floor heating, and snow melting systems. Special pricing applies to large orders, please call to see if you qualify for our "Bulk Order Discount"