§110.3 · Water heating equipment (mandatory)

# §110.3: Water heating equipment

What it requires

Every residential water heater installed in California must meet a minimum Uniform Energy Factor (UEF) for its category:

• Gas storage tank — UEF 0.64 minimum at 50-gal nominal capacity (the rating scales with tank size).
• Gas tankless / instantaneous — UEF 0.81 minimum (whole-home, ≥ 0.81 GPM rated).
• Electric storage tank — UEF 0.95 (small tanks) to 2.00+ (heat-pump water heaters).
• Heat-pump water heater (HPWH) — UEF 2.00+ minimum, with NEEA Advanced Water Heating Spec (Tier 3 or Tier 4) required when claimed as the §150.1(c) prescriptive solution.

§110.3 also sets ancillary mandatory requirements:

• Isolation valves on every tankless heater (so service techs can flush without depressurising the whole house).
• Hot-water pipe insulation ≥ R-3 on lines > ¾ inch.
• NEEA listing for HPWHs claimed as compliance solutions.

The mandatory floor in §110.3 stacks below the prescriptive equipment-type requirement in §150.1(c) (HPWH Tier 3 or Tier 4 by climate zone). See §150.0(n) for the mandatory installation-side rules.

When it applies

• Newly constructed residential, on every installed water heater.
• Alteration scope when the heater is being replaced — the new unit clears §110.3.
• Existing heaters NOT being replaced are grandfathered to the code at original install.

How we use it

When you check "Replace water heater?" on the Confirm step, we model a new unit at the §150.1(c) prescriptive tier — which clears §110.3 by design. When you leave it unchecked (the default on Add+Alt and Alteration scope), we keep the existing equipment in the model and the compliance verification report notes "Existing, no change" on the DHW row.

Common gotchas

• "Whole-home tankless" units rated for warm climates with a single-bathroom flow rate — winter cold-water inlet temps in CZ1, CZ11, CZ16 drop the effective UEF below the listed value.
• Garage-installed HPWHs in cold zones — the COP penalty isn't reflected in the lab-rated UEF, so the unit clears §110.3 on paper but underperforms in operation.
• Heat-pump water heaters spec'd at "Tier 2" thinking it's good enough — Tier 2 doesn't satisfy §150.1(c) prescriptive in any California zone; Tier 3 minimum, Tier 4 in the colder zones.