Water Heater Blanket and Hot Water Pipe Insulation: Title 24 Rules
Insulation added to an existing unfired water tank must have an installed R-value of at least R-3.5, or hold surface heat loss below 6.5 Btu per hour per square foot at an 80 degree F water-air difference. A contractor must certify in writing to the customer that it meets the rule.
- Choose your report
- Upload your plans
- Pay securely
- Permit-ready report by email
The blanket numbers
Section 110.8(d)2 covers external insulation installed on an existing unfired water storage tank. It needs an R-value of at least R-3.5, or the tank surface loss, based on an 80 degree F difference between water and air, must be under 6.5 Btu per hour per square foot. A home-center blanket labeled R-6 clears the first number; one labeled R-2 does not. Follow the manufacturer's instructions about vents, burners and controls.
The paper trail
If a contractor installs the insulation on an existing attic, duct or water heater, the contractor must certify to the customer, in writing, that it meets the applicable requirements (Section 110.8(d)). That sentence names contractors, but the same numbers describe a compliant blanket for anyone. Whether the work needs a permit is the building department's call.
Hot water pipes
- Domestic hot water piping insulation follows Section 609.12 of the California Plumbing Code (Section 150.0(j)1A).
- Pipe through framing members needs no insulation for the thickness of the framing. Metal framing needs grommets, plugs or wrapping so the pipe never touches it.
- Pipe in walls built to the quality insulation installation requirements is excepted.
- Pipe surrounded by 1 inch of wall insulation, 2 inches in a crawlspace or 4 inches in an attic needs none.
Replacing the heater changes the pipe rule
When a water heater is replaced or altered, newly installed pipes and existing accessible pipes must meet the Section 150.0(j)1 insulation rule (Section 150.2(b)1H i). For additions, existing inaccessible pipe does not need insulation (Exception 2 to Section 150.2(a)). A recirculation loop is hot water piping and gets the same insulation; in an alteration only demand recirculation with manual on/off control is allowed prescriptively (Section 150.2(b)1H ii).
Related reading
See water heater requirements, hot water recirculation and adding a second heater. Our residential reports cover jobs that replace the unit itself.
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
New unfired tanks must already have external R-3.5, combined internal and external R-16, or heat loss under 6.5 Btu per hour per square foot (Section 110.3(c)3), so a blanket matters mainly on an older tank without that insulation.
No. Existing inaccessible piping is excepted in the alteration and addition rules. Only newly installed and accessible existing pipe must be insulated.
Explore Water Heaters
- Do I Need Title 24 for a Water Heater Permit?
- Is California Banning Gas Water Heaters? What Title 24 and Air Districts Say
- 120-Volt or 240-Volt Heat Pump Water Heater: What Title 24 Allows
- Adding a Second Water Heater for a Far Bathroom: Title 24 Rules
- Can an Existing Water Heater Serve a New Addition?
View all Water Heaters guides → · HVAC and Water Heating · Title 24 guide