I am replacing my old PB pipes with pex. The original plumbing has the cold water line running between the shut off valve (outside) directly to the water heater. This line is under the slab. My new pex line will entering the house at a different point to avoid the slab. My question is, do I need to run the cold water line directly to the water heater first or can I connect at a different point. Most sample riser diagrams show the Water heater near the main cold water input, but is that just for convience or is it necessary for the system to function properly.
Thanks,
Tom,

Hello Tbamhi,

No, you don't have to run cold water line directly to the water heater from the source. Water heater is another plumbing fixture in the house so run your cold water a per the convenience of installation and house design. However, water heater should have 3/4" water supply as a feed.

Inside diameter of PEX pipes is slightly smaller than in copper of galvanized pipe. You want to assure that you have enough volume entering the water heater. Therefore, I would run 1" PEX from the source, distribute to other plumbing fixtures along the way and finish at the heater. I would reduce to 3/4" at the heater, above the shut off valve.

Hope that helps

Milo