2021 IECC Section C404
Service water heating is the hot water for sinks, showers, dish machines, and laundry, and it is a large energy load in apartment buildings, community kitchens, and clinics. Section C404 of the 2021 IECC covers four things: the efficiency of the heating equipment, insulation of the hot water piping, how far a fixture may sit from a source of hot water, and the controls on circulation loops, pools, and spas. Plumbing codes govern how the piping is sized and installed (Houston enforces the Uniform Plumbing Code; see the Commercial Plumbing course), so C404 asks a different question: how much energy does this system waste?
Water heaters, boilers, and storage tanks must meet Table C404.2, and the efficiency is verified with manufacturer data or an approved equipment rating program (C404.2). The table is mostly equations by equipment type and size, so plan review works from the listing and the rating label. A few values are worth knowing: unfired storage tanks need R-12.5 insulation, gas and oil pool heaters need 82 percent thermal efficiency, heat pump pool heaters need a 4.0 COP, and larger gas storage water heaters (input over 75,000 Btu/h) need 80 percent thermal efficiency.
C404.2.1 adds a higher bar for big gas-fired plants in new buildings. Where one gas-fired unit serves the whole building at 1,000,000 Btu/h or more, thermal efficiency must be at least 92 percent. Where several units serve the building and their combined input is 1,000,000 Btu/h or more, the input-weighted average must be at least 90 percent. The requirement does not apply where at least 25 percent of the annual service water heating comes from on-site renewable or site-recovered energy. Dwelling-unit heaters, and any heater of 100,000 Btu/h or less, are not counted in the building total.
A storage tank with vertical inlet and outlet pipes needs heat traps, either built into the tank or formed in the piping, so hot water does not thermosiphon up the pipes and cool off (C404.3). Connections to a solar loop are exempt. Under C404.4, piping from the heater to the end of each fixture supply is insulated per Table C403.12.3, and on both the inlet and outlet of a storage heater or tank, the piping to a heat trap, or the first 8 feet, whichever is less, must be insulated. Insulation is continuous except where the pipe passes through a framing member.
In Table C403.12.3, water at 105 to 140°F, which covers most service hot water, needs 1.0 inch of insulation on pipe under 1.5 inches and 1.5 inches on pipe from 1.5 to under 4 inches (using insulation within the stated conductivity range). Exceptions to insulation include the last tubing to a fixture, valves, pumps, strainers, and threaded unions on piping of 1 inch or less, piping from a user-controlled shower or bath mixing valve, cold-water piping of a demand recirculation system, piping at a vertical support, and piping surrounded by building insulation of R-3 or more. Thickness may not be reduced below what freeze protection or protection from hot surfaces requires.
Long dead legs waste water and heat while people wait for hot water. C404.5 limits the flow through small tubing (1/4 inch, 0.5 gpm; 5/16 inch, 1 gpm; 3/8 inch, 1.5 gpm) and then requires either the length method or the volume method. Both measure from the nearest source of heated water, which includes the heater, a recirculation loop, or a heat-traced pipe, to the end of the fixture supply.
Under the length method (Table C404.5.1) the largest pipe size in the run sets the maximum length. For fixtures other than public lavatories, 1/2 inch allows 43 feet, 3/4 inch allows 21 feet, 1 inch allows 13 feet, and 1 1/2 inch allows 6 feet. A public lavatory faucet is much tighter: 2 feet for 1/2 inch and 0.5 foot for 3/4 inch and larger. Under the volume method (C404.5.2) the water held in the pipe may not exceed 2 ounces to a public lavatory faucet or 0.5 gallon (64 ounces) to any other fixture, using the volume per foot from Table C404.5.1 or C404.5.2.1. Use one method for a run, not both.
Worked example. A community kitchen sink sits 24 feet from a recirculation loop. With 3/4 inch Type L copper (3.22 ounces per foot), the volume is 24 x 3.22 = 77 ounces, which is more than 64 ounces, and 24 feet also exceeds the 21 foot length limit for 3/4 inch pipe. With 1/2 inch Type L copper (1.55 ounces per foot) the volume is 24 x 1.55 = 37 ounces, under the limit, and 24 feet is under 43 feet. Options are a smaller branch, a shorter run, or extending the loop closer to the sink.
A circulation loop keeps hot water near the fixtures, but a loop that runs all day loses heat continuously. C404.6.1 requires a circulation pump, a return that is a dedicated pipe or a cold water supply pipe, and bans gravity and thermosiphon circulation. Controls must turn the pump off automatically when the water in the loop is at the desired temperature and there is no demand for hot water, and must keep water entering the cold water piping to 104°F or less. A demand recirculation system starts its pump from a user action, a sensor that detects a person at the fixture, or flow of hot water (C404.6.1.1). Electric heat trace must follow IEEE 515.1, adjust its input automatically to match when hot water is used, and turn off when there is no demand (C404.6.2). A pump moving water between a heater and a storage tank may run only from the start of the heating cycle to 5 minutes after it ends (C404.6.3). Controls, sensors, and pumps need to be in accessible locations.
Drain water heat recovery units must comply with CSA B55.2 with a pressure loss under 10 psi at maximum design flow (C404.7). For pools and permanent spas (C404.8), each electric heater needs an on-off switch that is part of the heater, on its exterior, or within 3 feet of it with ready access, and a gas heater may not have a continuously burning pilot. Heaters and pump motors need time switches, except where public health rules require 24-hour pump operation. Outdoor heated pools and spas need a vapor-retardant cover unless more than 75 percent of the heating energy over a season of at least 3 months comes from a heat pump or on-site renewables. Portable spas follow APSP 14 (C404.9).
The energy code says nothing about a degree setting at a public lavatory; its public lavatory rule is the tight 2 ounce and 2 foot piping limit above, which keeps the wait short and the waste small. Water temperature at public lavatories is a plumbing code matter. The 2021 International Plumbing Code (Section 419.5) requires tempered water through a listed limiting device at lavatories in public toilet facilities, and the adopted plumbing code sets the actual value. Check both codes, and remember that local adoption governs.
In the field
A GCHS rehab of a 12-unit senior apartment building replaces a failing central water heater and adds a recirculation loop. The design has a 3/4 inch branch of 30 feet to the community room kitchenette sink. Plan review checks the heater listing and efficiency, the heat traps, and whether the sink is inside the length or volume limit; at 3/4 inch and 30 feet it fails both, so the branch goes to 1/2 inch or the loop is extended. In the field the inspector confirms the first 8 feet of pipe on each side of the tank are insulated, that the loop has a control that shuts the pump off at temperature (a pump running on a plug and no control is a common find), and that the return is a real return, not a gravity loop.
1. A new Group B community building has one gas-fired water heater serving the whole building, with an input of 1,200,000 Btu/h and no on-site renewable or site-recovered energy. What minimum thermal efficiency does C404.2.1 require?
2. Three gas-fired water heaters of 500,000, 400,000, and 300,000 Btu/h serve a new Group B building. Under C404.2.1, what minimum thermal efficiency must their input-weighted average meet?
3. A new Group B building has a 1,100,000 Btu/h gas-fired water heating plant, and on-site solar thermal panels supply 30 percent of its annual service water heating. What follows under C404.2.1?
4. Which tank connection is not required to have a heat trap under C404.3?
5. An inspector checks a storage water heater with vertical inlet and outlet piping in a Group B community building. Under C404.4, how much of the inlet and outlet piping must be insulated at minimum?
6. A 1-inch nominal hot water pipe carries 120°F water in a Group B building. Using Table C403.12.3 and insulation within the stated conductivity range, what minimum insulation thickness applies?
7. An inspector finds a 3-inch hot water main at 130°F covered with 1.0 inch of insulation within the stated conductivity range. What does Table C403.12.3 require?
8. Which of these piping runs is excepted from tubular pipe insulation under C404.4?
9. A 3/4 inch hot water branch runs from a recirculation loop to a kitchen sink in a Group B community kitchen. Under the length method in Table C404.5.1, what is the maximum allowed length for fixtures other than public lavatories?
10. Under the volume method in C404.5.2, what is the maximum water volume in the piping from the nearest source of heated water to a fixture other than a public lavatory?
11. A plans reviewer checks a 30 foot run of 1/2 inch Type L copper (1.55 ounces per foot per Table C404.5.2.1) from a recirculation loop to a break room sink. Using the volume method for a fixture other than a public lavatory, what is the result?
12. A recirculation pump in a Group B clinic runs 24 hours a day on a plug with no controls. What does C404.6.1 require that is missing?
13. Under C404.6.1, controls on a circulating hot water system must limit the temperature of water entering the cold water piping to not more than:
14. An outdoor heated pool at a Group R-2 apartment building in Zone 2A is heated by a gas heater, and none of its heating energy comes from a heat pump or renewables. What does C404.8.3 require?