2021 IPC Chapter 5
A storage water heater is a pressure vessel full of hot water, and Chapter 5 of the 2021 IPC is mostly about keeping it from becoming a hazard: getting to it, valving it, protecting it against overpressure and overtemperature, and making sure the water that leaks or is relieved goes somewhere safe. Heaters are one of the most common items in commercial rehab, so the discharge pipe and the pan are among the first things an inspector looks at. Fuel connections belong to other codes (the International Fuel Gas Code for gas, NFPA 70 for electric), and a heater is always installed per the manufacturer's instructions as well (502.1).
A heater must be located and connected so it can be seen, serviced, and replaced (501.4). The service side needs a level working space at least 30 inches by 30 inches in front of the control side, and access must not require removing permanent construction, other appliances, or unrelated piping (502.5). Heaters burning solid, liquid, or gas fuel may not sit in a room used as a plenum (502.2). Attics are the tightest case (502.3): an opening and passageway large enough to remove the heater, the passage at least 30 inches high and 22 inches wide and no more than 20 feet long from the opening to the heater, solid flooring at least 24 inches wide, and a level service space at least 30 inches by 30 inches at the front of the heater.
The cold water branch to each heater or storage tank needs its own valve, near the equipment, serving only that heater and reachable on the same floor (503.1). Closing it must not cut off cold water to the rest of the building. Every tank-type heater and storage tank also needs a drain valve at the bottom with at least a 3/4-inch inlet and a male garden hose outlet (501.3). The energy supply needs a shutoff too: an electric heater must have a disconnecting means per NFPA 70, and other types need a separate fuel shutoff valve (504.3).
A storage heater that runs above atmospheric pressure must have an approved, self-closing (levered) pressure relief valve and temperature relief valve, or a combination valve (504.4). These valves go in the shell of the tank, and the temperature sensing must be in the top 6 inches, where the hottest water sits. A separate storage tank needs its own valves, and there may be no check valve or shutoff valve between a relief valve and the tank it protects (504.4.1). The valve must carry the label of an approved agency, have a temperature setting of not more than 210°F, and a pressure setting no higher than the tank's rated working pressure or 150 psi, whichever is less. Its relieving capacity must equal or exceed the heater's heat input (504.5). A relief valve is a safety device only; it may not be used to control thermal expansion (504.4).
Worked example: a heater's plate reads a maximum working pressure of 125 psi, so the relief valve setting may not exceed 125 psi. A 300 psi storage tank is capped at 150 psi, the lower of the two limits.
The discharge pipe is where most field violations occur. It may not connect directly to the drainage system; it ends in an air gap in the same room as the heater. It runs at least as large as the valve outlet and full size to the gap, serves only one relief device, and drains by gravity without traps. It may not have valves, tees, or a threaded end, so no one can cap it. It discharges to the floor, the heater pan, a waste receptor, or outdoors, in a place where the flow will not hurt anyone or damage the building and where occupants can see it. The end stops not more than 6 inches, and not less than two pipe diameters, above the floor or the flood level rim of the receptor. Where the discharge is piped with insert fittings, use one nominal size larger than the valve outlet.
| The discharge pipe must | The discharge pipe must not |
|---|---|
| End at an air gap in the heater's room | Connect directly to the drainage system |
| Be full size from the valve to the gap | Be smaller than the valve outlet |
| Serve one relief device | Join another relief line |
| Drain by gravity, end where occupants can see it | Be trapped or hidden |
| End 2 diameters to 6 in above the floor or rim | Have valves, tees, or a threaded end |
For a 3/4-inch valve outlet, the pipe end must sit at least 1 1/2 inches and no more than 6 inches above the floor.
Where a leaking tank would cause damage, a storage heater goes in a pan. The pan may be galvanized steel or aluminum at least 0.0236 inch thick, plastic at least 0.036 inch thick, or another approved material, but plastic may not go under a gas-fired heater. It must be at least 1 1/2 inches deep and large enough to catch drips and condensate, and it drains through an indirect waste of at least 3/4 inch (504.7.1). The drain runs full size to an indirect waste receptor or floor drain, or to the outside ending 6 to 24 inches above the ground (504.7.2). A replacement heater does not need a pan drain if none was installed before.
The tank must be protected from siphoning, by a dip tube with a hole at the top or a vacuum relief valve above the tank (504.1); bottom-fed heaters and tanks need a vacuum relief valve (504.2). Heaters carry automatic, adjustable temperature controls (501.8). Water from a tankless heater for domestic use is limited to 140°F, which does not replace the shower valves of Lesson 4 (501.6). Where a combined space and water heating system runs above 140°F, a mixing valve holds the potable side at 140°F or less (501.2). Heaters must be third-party certified, and the maximum allowable working pressure must be permanently marked where it can be read (501.5, 501.7). Unfired hot water storage tanks are insulated to R-12.5 (505.1).
In the field
A GCHS rehab job replaces a gas water heater in a second-floor mechanical closet over an occupied unit. The old relief line is threaded on the end and tied into a floor drain. Both must change: the pipe needs a plain end with an air gap, not a threaded fitting, and it may not connect directly to the drain. If there was never a pan drain, the replacement heater does not need one added, but a pan is still wise over living space. Check that the shutoff valve is on the cold branch and reachable on that floor.
1. A gas-fired storage water heater is being inspected in the mechanical room of a Group B office. What is the highest temperature setting allowed on its temperature relief valve under Section 504.5?
2. A hot water storage tank in a Group R-2 laundry room is rated for 300 psi working pressure. What is the maximum pressure setting of its relief valve under Section 504.5?
3. In a Group A-2 restaurant, the temperature-sensing element of a new temperature relief valve is installed low on the side of the tank. What is wrong, per Section 504.4.1?
4. An inspector finds a full-port ball valve between the relief valve and the tank on a water heater in a Group R-2 mechanical room. Which conclusion is correct?
5. A relief valve discharge pipe in a Group B janitor closet is finished with a threaded male adapter so a hose can be attached. Under Section 504.6 this is:
6. The relief valve on a heater in a Group A-3 kitchen has a 3/4-inch outlet, and the discharge pipe is the same size. Where must the pipe end under Section 504.6?
7. A relief valve discharge pipe on a water heater in a Group B building is solvent-welded into a waste pipe that goes to the building drain. What is the finding under Section 504.6?
8. Two storage heaters in a Group A-3 kitchen have relief discharge lines that are joined into one 1-inch pipe to a floor drain. Under Section 504.6 this arrangement:
9. A plastic drain pan is proposed under a gas-fired storage heater in a Group R-2 second-floor closet. What does Section 504.7 say?
10. A storage water heater pan in a Group B office drains to the outdoors. Under Section 504.7.2, the drain must end how far above the adjacent ground?
11. A gas water heater is replaced in a Group R-2 unit that never had a pan drain. What does Section 504.7.2 require for the replacement?
12. A storage heater in a Group B building is being placed in an attic. The passageway from the opening to the heater measures 26 feet along its centerline. What is the finding under Section 502.3?
13. A water heater in a Group R-2 utility closet has only 24 inches of clear floor space in front of its control side. What does Section 502.5 require?
14. The cold water shutoff for a water heater in a Group R-1 hotel is located in a ceiling above the corridor on the floor below. What is the concern under Section 503.1?