Hotels heat water centrally and keep it moving. A recirculation loop runs hot water past each riser so no room is far from a source, and the plumbing code counts that loop as the source for its 50-foot limit. Tempering valves bring the water down at delivery, and a water management program keeps unused branches from stagnating.
Why does a hotel need a central plant sized for the peak?
Because everyone showers at once. A. O. Smith's guide to multi-dwelling hot water notes that "An adequate supply of hot water is a must in apartment houses, motels, hotels, dormitories, etc." It also says "Peak demand periods vary with the type of dwelling, apartments having a 3 hour period, hotels and motels a two hour period, dormitories & convention hotels/motels a one hour period."
That shapes the equipment. The heaters and storage are sized to cover the morning bathing rush, not the average hour. The same guide gives dormitories and convention hotels a one hour peak, which packs the same demand into less time. A plant undersized for its peak tends to show up as rooms running short at the busiest hour. Our page on why commercial water heaters run out of hot water covers that failure.
How does a recirculation loop get hot water to the far rooms?
The loop is a second pipe that carries hot water back to the plant, so hot water is always moving past the branch to each room. The plumbing code counts on that. Section 607.2 of the Phoenix plumbing code says "The developed length of hot or tempered water piping, from the source of hot water to the fixtures that require hot or tempered water, shall not exceed 50 feet." It then adds "Recirculating system piping and heat-traced piping shall be considered to be sources of hot or tempered water."
Put those two sentences together and the design logic is clear. Without a loop, a fixture more than 50 feet of pipe from the heater breaks the code. With a loop, the "source" is wherever the loop passes, so each branch to a room only has to be short. Heat-traced piping is the other option the code names.
Phoenix's published amendments to the 2024 IPC (Ordinance G-7397) change other sections, such as 403.2, 424.2 and 604.4, but do not list Section 607, so the base text applies. Other cities check their own edition.
The code also governs how a loop is controlled and piped:
- Demand recirculation. Section 607.2.2.2 says a system with pumps that return water from the heated supply pipe to the source "through a cold water supply pipe shall be a demand recirculation water system," with controls that start the pump on a user's signal or sensed flow and limit the temperature of water entering the cold piping to 104°F.
- Mixing valve piping. Section 607.2.3 says that where a temperature-actuated mixing valve is used with a recirculating pump, the return line has to be routed to specific connections.
- Insulation. Section 607.5 requires piping that carries heated water to be insulated, with the energy code setting the details.
How is the temperature kept safe at the room?
The usual way to square scald safety with Legionella control is to keep the plant hot and temper the water near the point of use. CDC's potable water module recommends to "Store hot water at temperatures above 140°F (60°C)," to "Ensure hot water in circulation does not fall below 120°F (49°C)," and to "Install thermostatic mixing valves as close as possible to fixtures." Maricopa County's plan-review guideline makes the same point: "The use of specific tempering valves enables an establishment to maintain hot water at 140°F or higher, thereby reducing the presence of Legionella inside hot water tanks and systems."
At the shower, the plumbing code requires a valve limited to a maximum of 120°F (IPC 412.3), and a tempered-water control set to no more than 110°F where tempered water serves washing fixtures (607.1.2). Our page on thermostatic mixing valves in commercial buildings explains the valve types, and how senior living facilities prevent shower scalding shows the shower side in detail.
What keeps the loop working over time?
Maintenance, mostly. A loop only helps where water actually moves, and a few things quietly defeat it.
- Dead legs. CDC says to "Eliminate dead legs, which are sections of no- or low-water flow," and to "Flush low-flow piping runs and dead legs at least weekly." Maricopa's guideline likewise says to minimize "dead legs" in plumbing lines to reduce stagnation. A closed wing or a block of rarely used rooms is an example. See what a dead leg is.
- Balance. A loop that is out of balance sends hot water down the easy path and starves the far risers. Our page on why an apartment building loses hot water on upper floors walks through the pump, balancing and valve failures, and the same ones apply in a hotel.
- Continuous circulation. CDC's list also says to "Recirculate hot water continuously, if possible."
- Point-of-use heaters for remote runs. The county guideline notes that "The installation of approved boilers or point-of-use water heaters may be required to ensure permitted facilities are provided with sufficient hot water for all operations."
Hot water at the room is also tied to the building's pressure. A booster or valve problem can make a shower feel weak even when the water is hot. See why hotel rooms on upper floors get low water pressure. For what the law requires of a hotel on hot water, read whether hotels have to provide hot water by law.