# §150.0(n): Domestic water heating
What it requires
The mandatory floor on the residential DHW side:
- Equipment must meet the UEF (Uniform Energy Factor) floor for its category, gas-storage, gas-tankless, electric-resistance, heat-pump.
- Hot-water distribution pipes ≥ ¾ inch carry a minimum R-value of insulation (typically R-3 for ≤ 1 in., R-5 for > 1 in.).
- Recirculation loops use demand-controlled pumps (push-button, motion, smart timer), never continuous.
- Heat-pump water heaters comply with the NEEA Advanced Water Heating Spec (Tier 1+) when they're claimed as the compliance solution.
When it applies
Every project with a water heater. The prescriptive package in §150.1(c) sets the equipment type (HPWH Tier 3 or Tier 4 by climate zone); §150.0(n) sets the floor under all paths.
When existing equipment grandfathers in
The most common DHW question in addition / alteration scope: do I need to replace the water heater? The answer is no, almost always, §150.2(b) treats DHW as a "componenent" alteration only when the equipment itself is being replaced. Adding fixtures, rerouting pipes, or even adding a bedroom does not trigger a heater swap.
How we use it
When you check "Replace water heater?" on the Confirm step, we apply the prescriptive package's required tier. When you leave it unchecked (the default for Add+Alt and Alteration scope), we keep the existing equipment in the model and the CF1R notes "Existing, no change" on the DHW row.
Common gotchas
- Whole-house demand recirc pumps installed without a control trigger §150.0(n) re-work, the AHJ inspector reads the spec sheet.
- Tankless gas water heaters that meet UEF but miss the §110 isolation-valve mandatory measure.
- Garage-installed HPWHs in cold climate zones, the COP penalty makes the Tier rating effectively lower in operation; on the prescriptive path the model still credits the labeled Tier, but the homeowner pays the real bill.