Water Heaters Both Codes Agree On — Relief Valves and Their Discharge, Pans, Shutoffs, Expansion Control, Attic Access (UPC ch. 5 + 608 / IPC ch. 5 + 607)
A storage water heater is a pressure vessel with a flame or an element under it. Both codes therefore spend their words on the same five things: the temperature-and-pressure relief valve and where its discharge may go, the drain pan, the shutoff valve on the cold supply, thermal expansion in a closed system, and access — especially in attics. The UPC keeps its relief-valve rules in chapter 6 (608.3–608.5) and its pan and access rules in chapter 5 (507–508); the IPC keeps almost everything in chapter 5 (501–504) with expansion control in 607.3. Fuel-gas matters (combustion air, venting, clearan
2018 UPC and 2018 IPC · Reviewed 2026-09-20
1. Relief valves
| Rule (both codes) | UPC | IPC |
|---|---|---|
| A storage water heater (or a water system with storage water-heating equipment) gets an approved, listed, adequately sized combination temperature-and-pressure relief valve (or separate temperature and pressure relief valves) | 608.3 | 504.4 |
| Pressure setting not more than 150 psi (IPC: or the manufacturer's rated working pressure, whichever is less) | 608.4 | 504.5 |
| The relief valve's discharge (relieving) capacity is not less than the heat input rating of the heater | 504.6 | 504.5 |
| No shutoff (or check) valve between the relief valve and the heater/tank — and none on the discharge line | 504.6, 608.4 | 504.4.1 |
| Installed per the valve's listing and the manufacturer's instructions (IPC: in the tank shell, temperature element sensing the top 6 in of the tank) | 504.6, 608.3 | 504.4.1 |
| The relief valve is not a means of controlling thermal expansion (IPC) / expansion is handled by a tank (UPC 608.3) | 608.3 | 504.4 |
The maximum water-heater temperature both codes work to is 210 °F: the IPC caps the T&P valve's temperature setting at 210 °F (504.5); the UPC's definition of a water heater is an appliance whose automatic controls limit the water to a maximum of 210 °F (225.0). Instantaneous (nonstorage) heaters with an inside diameter of not more than 3 in are excepted from the UPC's T&P rule.
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