Pipe sizing

Start at the pump

Do not neck down smaller than the pump ports unless approved. For many compact vans, 1/2 in supply lines work well; 3/8 in short fixture branches can conserve hot-water wait volume but may restrict higher flows.

Pressure loss

Count actual inside diameter, length, elbows, valves, cartridges and simultaneous use. Filter housings may have large ports but cartridges still impose pressure drop that grows as they load with sediment.

Hot-water wait

A larger hot line holds more cold water between heater and tap. Short routing often saves more water than oversized pipe. Place the heater near the shower/sink or consider a controlled recirculation design.

Oversizing

Huge pipe costs space, stores more stagnant water and does not overcome a small pump, restrictive filter or faucet aerator. Size the full path as a system.

Build rule

If you cannot reach it, isolate it, drain it and explain its pressure/temperature or water-quality job, it is not ready to hide behind a wall.

CHAPTER CHECK

• I can explain the purpose and failure mode of each item in this chapter. • I know which manufacturer limit or water-quality claim controls my choice. • I added the valve, access, drain, measurement or maintenance task to my drawing/checklist.