4.3 Water Heater Pans, Pan Drains, and Storage Tank Requirements

When a pan is required

IPC 504.7 states the trigger condition rather than a list of locations:

Where a storage tank-type water heater or a hot water storage tank is installed in a location where water leakage from the tank will cause damage, the tank shall be installed in a pan.

The judgment is about consequence, not about floor level. A heater in a finished basement above a finished ceiling needs a pan. A heater in a detached, unfinished, sloped-to-drain utility shed generally does not. Local jurisdictions frequently make the requirement universal for interior installations; the code text itself is conditional.

Note two words: storage tank-type. A wall-hung tankless heater is not a storage tank-type water heater, so 504.7 does not reach it on its face — though manufacturers often require drainage protection independently, and IPC 301.7 makes the more restrictive provision control.

Pan material and thickness

The plastic prohibition under gas-fired heaters exists because a pan directly under a burner compartment can be exposed to flame rollout and to radiant heat from the draft hood area.

Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(bb) adds a sentence permitting a pan that would otherwise be barred if it is constructed of material having a flame spread index of 25 or less and a smoke-developed index of 450 or less tested to ASTM E84 or UL 723. Rule 1.2(E)(1)(aa) adds an exception for replacements of water heaters that did not have a pan previously installed to the code in effect at the original installation. Answer the model code on the exam.

Pan size and drain — IPC 504.7.1

• The pan shall be not less than 1-1/2 inches in depth.
• It shall be of sufficient size and shape to receive all dripping or condensate from the tank or water heater.
• It shall be drained by an indirect waste pipe having a diameter of not less than 3/4 inch.
• Piping for safety pan drains shall be of the materials listed in IPC Table 605.4.

"Indirect waste pipe" is the operative phrase. The pan drain is an indirect waste under IPC Chapter 8, so it may never connect directly to the drainage system; it terminates over a receptor with an air gap or air break. That places pan drains in the same family as relief valve discharge and condensate drainage.

Pan drain termination — IPC 504.7.2

The pan drain shall extend full size and terminate over a suitably located indirect waste receptor or floor drain, or extend to the exterior of the building and terminate not less than 6 inches and not more than 24 inches above the adjacent ground surface. Where a pan drain was not previously installed, a pan drain shall not be required for a replacement water heater installation.

Two dimensions, both frequently confused with the relief-valve rule of 504.6:

Six inches is a maximum in one rule and a minimum in the other. Read the question carefully.

The replacement exemption is a practical, retroactivity-limiting rule: swapping a heater in a house that never had a pan drain does not compel you to cut a new drain line through finished construction. It does not exempt you from the pan itself.

Where the relief valve may discharge

IPC 504.6 item 5 expressly allows relief discharge "to the pan serving the water heater or storage tank." That is why a correctly built installation often shows one 3/4-inch line from the T&P valve terminating over the pan, and a separate 3/4-inch pan drain running to a receptor. What is not permitted is tying the relief discharge into the pan drain piping — item 4 requires the discharge to serve a single relief device and not connect to piping serving other equipment.

Separate storage tanks

Where a system uses a water heater plus a separate storage tank:

• IPC 504.4.1 requires an approved self-closing levered pressure and temperature relief valve (or combination) on both the storage water heater and the storage tank.
• IPC 504.7 applies the pan requirement to a "hot water storage tank" in its own right.
• IPC 503.2 requires the connection method to provide proper circulation of water through the heater.
• IPC 505.1 requires unfired hot water storage tanks to be insulated to R-12.5.
• IPC 607.2.1.1 limits the pump that circulates between the heater and the storage tank to operating not greater than 5 minutes after the end of the heating cycle.

Worked example: sizing and routing the drains

A 75-gallon electric storage water heater sits on a second-floor mechanical closet slab above a finished dining room. The nearest floor drain is 14 feet away in the same closet's neighboring laundry.

1. Pan required? Yes — leakage will damage the ceiling below (504.7).
2. Pan material? Galvanized steel at 0.0236 inch or plastic at 0.036 inch. The heater is electric, so plastic is permitted.
3. Pan depth? Not less than 1-1/2 inches, sized to catch all dripping and condensate (504.7.1).
4. Pan drain? Not less than 3/4 inch, indirect waste, of a Table 605.4 material, full size to its termination (504.7.1, 504.7.2).
5. Termination? Over the laundry floor drain with an air gap, since an interior receptor is available. If it were routed through the exterior wall instead, the outlet would have to land 6 to 24 inches above the adjacent ground.
6. Relief valve discharge? A separate 3/4-inch line, not tied into the pan drain, terminating either over the pan or to the floor — not more than 6 inches above, and not less than 1-1/2 inches above, with no threaded end and no valve.
7. Thermal expansion? If the cold supply passes a check valve, pressure reducing valve or backflow preventer, an expansion control device is required downstream of them (607.3) — covered in the next section.