Can an Existing Water Heater Serve a New Addition?
Yes, when the addition does not add a second water heater. One existing heater may feed the new rooms, and the requirement that follows is insulation on the new hot water piping. Installing an additional water heater changes the answer: it must then be one of the types listed in Section 150.2(a)1D.
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The deciding question: second heater or not
Section 150.2(a)1D applies only when an additional water heater is installed as part of the addition. Extending hot water piping from the existing tank triggers nothing of the kind.
If the existing heater stays
Additions carry the mandatory pipe insulation rule of Section 150.0(j)1, which points to California Plumbing Code 609.12 for domestic hot water. Existing piping you cannot reach is excused (Exception 2 to Section 150.2(a)). New piping is also excused where it is surrounded by 1 inch of wall insulation, 2 inches in a crawlspace or 4 inches in an attic, or for the short distance where it passes through framing members.
If the pipe run is too long
A distant addition raises the wait for hot water. The manual offers two answers for an alteration: a demand recirculation system with manual on and off control, or a gas or propane tankless heater nearer the fixtures. A timer or temperature-controlled loop needs the performance approach. See hot water recirculation.
If the old heater is being replaced anyway
Replacing it alongside the addition is a separate alteration under Section 150.2(b)1H. The manual's 1,500 square foot house with a 500 square foot addition and a new 50-gallon gas heater qualifies as a gas replacement, with piping insulated (Example 9-31).
If a second heater goes in
The prescriptive options are a single heat pump water heater, a NEEA Tier 3 heat pump unit, or in additions of 500 square feet or less an electric heater with point-of-use piping. A gas tankless heater of 200,000 Btu/h or less is not among them (Example 9-32). Details are in the heat pump water heater guide. Anything else goes through performance modeling.
See also water heater requirements, existing HVAC in an addition, room additions and residential reports.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
Not necessarily. If the existing heater serves the addition, the code asks for insulated new piping. A second heater is a choice, and it then must be one of the listed types.
Not prescriptively. The manual says an instantaneous gas unit of 200,000 Btu/h or less is not an allowed type for an additional heater, so it would need performance modeling.
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