Hot water plumbing layout: max 0.6 gal of water stored in pipe between water heater + any fixture
WaterSense Homes §Hot Water Distribution — ≤ 0.6 gal stored in pipeDescription
WaterSense V2 requires that the volume of water stored in the hot water supply pipe between the water heater and ANY hot-water fixture be no greater than 0.6 gallons. Practical implications: use smaller-diameter pipe (½-in vs ¾-in PEX where allowable); use a manifold / home-run plumbing system; locate the water heater near the central bath/kitchen cluster; OR use a recirculation system with demand control. Verified by either a fixture-by-fixture water-volume test or compliance with a pre-approved plumbing layout.
Why this exists
Up to 30% of hot water use is the water sitting cold in the pipe between the heater and the tap (and then dumped down the drain waiting for hot to arrive). Compact / manifolded plumbing layouts dramatically reduce this waste — and shorter wait times are a usability win too. Architects should integrate the water heater location into the early floor plan, not as an afterthought.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
maxStored | max | 0.6 | gal in pipe | Max water volume stored in hot-water pipe to each fixture |
Categories
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Slab-on-grade vapor barrier + capillary break required · HUD RSDG §4.6
- Roof overhangs protect walls — 12-24 inches in humid climates; one foot per story below · HUD RSDG §5.6.5
- ENERGY STAR certification: HERS-index target + Rater field checklist + HVAC quality install · ENERGY STAR SFNH §Overview — Certification path
- Grade I insulation installation: no gaps, no compression, fully filling cavity, supported aligned with air barrier · ENERGY STAR SFNH §Rater Field Checklist — Section 1 (Insulation + Air Barrier)
- Continuous air barrier on all six sides of conditioned space — including rim joists, knee walls, attic floor · ENERGY STAR SFNH §Air Barrier — continuous on all six sides of every conditioned space
Last reviewed 2026-05-15.