How does Title 24 affect water heaters?

Title 24 strongly shapes water-heater selection for ADUs. For most new dwelling units, the prescriptive baseline is a heat-pump water heater (HPWH), because it is the most efficient option and scores best in the energy model. Other equipment is allowed, but choosing something other than a HPWH often pushes you onto the performance path or specific exceptions.

Why the heat-pump water heater is the baseline

• Efficiency. An HPWH is roughly two to three times more efficient than electric-resistance water heating, which is exactly what the energy model rewards.
• Electrification policy. Title 24 and many local reach codes favor all-electric water heating in new ADUs, and a number of cities prohibit gas water heaters in new construction altogether.
• Compliance simplicity. Specifying an HPWH is usually the most direct path through the prescriptive requirements.

Other options and their conditions

• Tankless (instantaneous). Common in compact ADUs for space reasons. Gas units need proper venting and a gas line sized for high BTU demand; electric units need a substantial 240V circuit. They must meet the applicable efficiency thresholds and often rely on the performance path or a space-constraint exception.
• Storage tank (electric resistance). Valid but less common in new construction, since it performs worse in the model and typically must be offset elsewhere on the performance path.
• Space-constrained small ADUs. The code provides allowances in some small-footprint situations where a heat-pump water heater cannot reasonably be installed — verify the specifics for your code cycle and floor area.

How it flows into your plumbing plans

The CF1R fixes the water-heater type and efficiency, and your plumbing plans then reflect it: the fixture/equipment schedule lists the water heater make, model, capacity, and efficiency; the water supply and DWV layouts account for its location; and an HPWH installation needs adequate surrounding air volume and condensate handling. If the plumbing plans specify a water heater that doesn't match the CF1R, the plan checker issues a correction.

Practical example: an all-electric 700 SF ADU in a city with a gas ban, designed with a heat-pump water heater on a dedicated 240V circuit, located where it has the air volume and condensate drainage it needs — a clean, code-aligned solution.

The applicable code cycle and local amendments vary — confirm with your local building department, including whether a gas ban applies. We coordinate the water-heater specification between the CF1R and your plumbing sheets through the +$240 Title 24 add-on, prepared alongside your MEP plans.