In the Field · Part 4
Water heaters II: tankless and heat pump. Gas sizing, venting, condensate, the 2025 Energy Code direction, and where the gas-ban ordinances stand
The two water heaters that are not a tank each turn a four-hour swap into a design job. A gas tankless unit draws four to six times the input of the tank it replaces, so the gas line, the venting, and the condensate drain are the job, not the heater. A heat pump water heater draws almost no gas and instead needs a 240-volt circuit, air, a place for the condensate, and a customer who understands recovery time. Both are where California's energy policy is pointed: the 2025 Energy Code makes heat pump water heating the prescriptive baseline for new homes and additions. And both are the subject of local politics: the Berkeley gas ban was struck down in federal court in 2023 and repealed, and the South Coast air district's proposed zero-NOx water heater rule was voted down in June 2025. This lesson gives the method for each unit and the current state of the rules so the sale is honest.
What the full lesson covers
- Tankless gas: size the gas line for the unit's full input on the longest run of the whole system (CPC 1215.1.1); most 1/2-inch branches that fed a 40,000 BTU tank cannot feed a 150,000 to 199,000 BTU tankless, and a new 3/4-inch or 1-inch run from the meter is normal.
- Tankless venting is Category III or IV per the listing, with the listed vent material, terminations, and clearances; condensing units produce acidic condensate that goes to an approved drain (CPC 814.1), through a neutralizer where the AHJ or the manufacturer requires it.
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More lessons in The Field: Method, Code, and Cases
- 1The diagnostic method: verify, isolate, cheapest test first, cause not symptom, the options ladder, document
- 2Permits: when one is required, what is exempt, pulling it online, the inspection sequence, what inspectors look for, and handling corrections
- 3Daily-use code: drainage slope, venting, water sizing, cleanouts, trap arms, and fixture units, with the section for each
- 4Gas piping in practice: sizing, CSST bonding, the pressure test, appliance connectors and shutoffs, sediment traps, and seismic shutoff valves