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Home / Code Guides / Water Heater Installation

Water Heater Code — T&P Valve, Discharge Pipe, Drain Pan & Strapping

Water heater inspections turn on four things: the relief valve, where its discharge pipe ends, the pan under the tank, and whether the tank is strapped. Almost every correction notice is one of those four.

WATER HEATER — T&P DISCHARGE, PAN AND SUPPORTSD40WATER HEATER6" MAXT&P relief valve§504.4Discharge pipenot smaller than the valve outlet; full size to the air gapEnd 2 × pipe dia. MIN above floorno threaded end, valves or tee fittingsSeismic supportslocations per IBC design and manufacturerDrain pan (where required)T&P DISCHARGE PIPE — IPC §504.6Not directly connected to the drainage system; dischargesthrough an air gap in the same room as the heater.Serves a single relief device; not trapped; flows by gravity.Ends at the floor, water heater pan, waste receptor or outdoors,6" MAX above and 2 × pipe dia. MIN above the floor or floodlevel rim.Termination readily observable by occupants.RELIEF VALVE AND SUPPORTSHeater has an approved, self-closing pressure and temperaturerelief valve (§504.4).Where earthquake loads apply, supports designed for the seismicforces in the IBC (§502.4).Strap locations and the drain pan are not dimensioned here.Drain pan requirements are not reproduced here; verify with the current edition.Air gap drawn to scale; tank schematicWATER HEATER · IPC 2021 §502.4 · §504.4 · §504.6
T&P discharge, drain pan and strapping — IPC 2021 504. The IRC states the same requirements at P2804 and P2801.Open full diagram →
RequirementModel Code StandardSection
Relief valveThe temperature and pressure relief valve must open at no more than 210°F and at a pressure at least 25 psi above system pressure but not over 150 psi, with the temperature element in the top 6 in. of the tankIRC P2804.3, P2804.4
Nothing in the wayNo check valve or shutoff may be installed between the relief valve and the tank, or in the discharge lineIRC P2804.6
Discharge pipingDischarge piping must run full size to an approved point, terminate no more than 6 in. and no less than two pipe diameters above the receiving surface, discharge through an air gap in the same room as the heater, and end without threadsIRC P2804.6.1
Drain panWhere a leak would damage the structure, the heater sits in a pan of galvanized or aluminum sheet at least 0.0236 in. thick, or plastic at least 0.036 in.IRC P2801.6
Pan drainThe pan is at least 1-1/2 in. deep with a drain of at least 3/4 in., though a replacement heater is excepted where no pan drain previously existedIRC P2801.6.1
Seismic bracingIn Seismic Design Categories D0, D1 and D2, and for townhouses in category C, the tank is braced at the upper and lower third of its height to resist one-third of its operating weightIRC P2801.8
Garage elevationIn a garage, an ignition source must sit at least 18 in. above the floor unless the appliance is listed as flammable-vapor-ignition resistantIRC P2801.7

Worth knowing

  • The pan-drain exception is the most-missed line in the chapter. Swapping a heater in a location that never had a pan drain does not oblige you to add one — but it does not excuse the pan itself.
  • Mid-tank strapping does not comply. The code asks for restraint at the upper and lower thirds, which is two straps at specific heights, not one strap around the middle.
  • The IRC sets no general maximum water temperature at the heater. The 140°F and ASSE 1017 mixing-valve requirements people cite are conditional, attaching to solar preheat and to combined space-heating systems, and the limits that protect bathers live in the fixture chapter.
  • A water heater in a bedroom or bathroom is not flatly prohibited. A fuel-burning unit needs a sealed enclosure with combustion air from outside, direct-vent appliances are exempt, and the fuel-gas chapter lists further exceptions.
  • Chapter 28 was renumbered for the 2024 edition, moving the pan requirement from P2801.6 to P2801.5. Some third-party pages labeled 2021 already print the 2024 numbers.

Common questions

What does the code say about relief valve for Water Heater Installation?

The temperature and pressure relief valve must open at no more than 210°F and at a pressure at least 25 psi above system pressure but not over 150 psi, with the temperature element in the top 6 in. of the tank. (IRC P2804.3, P2804.4)

What does the code say about nothing in the way for Water Heater Installation?

No check valve or shutoff may be installed between the relief valve and the tank, or in the discharge line. (IRC P2804.6)

What does the code say about discharge piping for Water Heater Installation?

Discharge piping must run full size to an approved point, terminate no more than 6 in. and no less than two pipe diameters above the receiving surface, discharge through an air gap in the same room as the heater, and end without threads. (IRC P2804.6.1)

Adopted edition by state

Base-code year from BuildSpec’s adoption records. States often amend the base code, and your city or county may differ, so confirm with your building department.

Related sections and guides

This guide is BuildSpec’s own summary, not code text. It cites the 2021 International Residential Code and the 2023 National Electrical Code as model standards. The IRC 2021 text itself is in the Code Library for signed-in members; BuildSpec publishes no NEC text, which is at nfpa.org.Neither is an adoption record: your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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