4.2 Relief Valves and Discharge Piping

The four safety devices of Section 504

IPC Section 504 requires four distinct protections, and exam items often turn on telling them apart.

The relief valve itself

IPC 504.4: storage water heaters operating above atmospheric pressure shall be provided with an approved, self-closing (levered) pressure relief valve and temperature relief valve or combination thereof, conforming to ANSI Z21.22. And then the sentence that decides a whole category of exam items:

The relief valve shall not be used as a means of controlling thermal expansion.

A T&P valve that weeps every afternoon is not a working expansion control; it is a symptom of a closed system that needs the thermal expansion device required by IPC 607.3.

IPC 504.4.1 Installation:

• Valves are installed in the shell of the water heater tank.
• Temperature relief valves shall be located in the tank so as to be actuated by the water in the top 6 inches of the tank served. Heat stratifies; the hottest water is at the top, so that is where the sensing element must reach.
• For installations with separate storage tanks, an approved self-closing levered pressure and temperature relief valve (or combination) conforming to ANSI Z21.22 must be installed on both the storage water heater and the storage tank.
• There shall not be a check valve or shutoff valve between a relief valve and the heater or tank served.

IPC 504.5 Relief valve approval: temperature and pressure relief valves, combinations thereof, and energy cutoff devices shall bear the label of an approved agency and shall have:

• a temperature setting of not more than 210 degrees F, and
• a pressure setting not exceeding the tank or water heater manufacturer's rated working pressure or 150 psi, whichever is less.

The relieving capacity of each pressure relief valve and each temperature relief valve must equal or exceed the heat input to the water heater or storage tank. A 199,000 Btu/h commercial heater cannot be protected by a valve rated for 100,000 Btu/h of relief.

Discharge piping — the fourteen rules of IPC 504.6

This list is the single densest source of Water Heaters exam items. Learn it as a list; items frequently ask which one of four statements is not permitted.

The discharge piping serving a pressure relief valve, temperature relief valve or combination thereof shall:

1. Not be directly connected to the drainage system.
2. Discharge through an air gap located in the same room as the water heater.
3. Not be smaller than the diameter of the outlet of the valve served, and shall discharge full size to the air gap.
4. Serve a single relief device and shall not connect to piping serving any other relief device or equipment.
5. Discharge to the floor, to the pan serving the water heater or storage tank, to a waste receptor or to the outdoors.
6. Discharge in a manner that does not cause personal injury or structural damage.
7. Discharge to a termination point that is readily observable by the building occupants.
8. Not be trapped.
9. Be installed so as to flow by gravity.
10. Terminate not more than 6 inches above and not less than two times the discharge pipe diameter above the floor or flood level rim of the waste receptor.
11. Not have a threaded connection at the end of such piping.
12. Not have valves or tee fittings.
13. Be constructed of materials listed in IPC Section 605.4, or materials tested, rated and approved for such use per ASME A112.4.1.
14. Be one nominal size larger than the relief valve outlet where the discharge piping is installed with insert fittings; the outlet end of such tubing shall be fastened in place.

Working rule 10

Rule 10 is the one most often misremembered as a flat "between 1-1/2 and 6 inches." It is not flat — the lower bound scales with pipe size.

A 3/4-inch discharge terminating 1 inch above the floor fails the minimum. A 1-inch discharge terminating 1-1/2 inches above the floor also fails, because two times 1 inch is 2 inches.

Why rules 11 and 12 exist

No threaded end (rule 11) prevents someone from capping the discharge. No valves or tees (rule 12) prevents both isolating the discharge and combining two relief devices into one line, where a discharge from one could back-pressure the other. Rule 4 says the same thing from the other direction: one pipe, one device.

Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(y) adds Colorado section 504.6.1 Collection of Relief Valve Discharge, requiring a means to capture relief valve discharge and convey it to the sanitary drainage system or the exterior by gravity or a pumped discharge, with exceptions for replacements of existing water heaters and where a water-sensing device wired to a normally closed solenoid valve in the supply piping is placed in the drain pan. Rule 1.2(E)(1)(z) adds 504.6.1.1, requiring such pumps to have an operating temperature at or above the relief discharge temperature and a gpm rating equal to or greater than the relief valve discharge. The model IPC has no equivalent, so answer from the 14-item list on the exam.

Worked example: inspecting a basement installation

A 50-gallon gas water heater in an unfinished basement has:

• a combination T&P valve in the top tapping, labeled 210 F / 150 psi — complies with 504.5, and the top tapping puts the element in the top 6 inches per 504.4.1;
• a 3/4-inch CPVC discharge line running from the valve down the side of the tank, through a 90 at the floor, across 8 feet, and terminating 7 inches above the floor over a floor drain, with a threaded adapter and cap on the end.

Findings:

• Rule 10 violation — the termination is 7 inches above the floor; the maximum is 6 inches.
• Rule 11 violation — there is a threaded connection at the end of the piping.
• Rule 1 and 2 check — the line discharges over the floor drain, not into it, so the air gap is intact; that part complies.
• Material: CPVC is listed in IPC Table 605.4 for hot water distribution, so rule 13 is satisfied.
• Corrective action: remove the threaded adapter and cap, and shorten the termination to not more than 6 inches and not less than 1-1/2 inches (2 x 3/4 inch) above the floor.