A new laundromat needs separate hot and cold supplies sized for peak demand, backflow protection on every washer, standpipe or trench drains with a lint interceptor, and floor drains with a 3-inch outlet. In Phoenix and Mesa, the service itself often needs a backflow assembly too. Washer manufacturers set the flow and pressure.
What water supply does a laundromat need?
Enough for everything running at the same time, with hot and cold kept separate. Phoenix's 2024 IPC Section 604.3 says the water system "shall be designed, and pipe sizes shall be selected such that under conditions of peak demand," fixture outlets get the flow in Table 604.3. Clothes washers are not in that table. For appliances not listed, flow and pressure "shall be in accordance with the manufacturer's installation instructions."
So the machine makers set your numbers, and they do not all agree. Dexter's vended washer manual says "Separate hot and cold water lines must be supplied to the machine," at 30 to 120 psi, and recommends a 140°F hot supply "for best washing results" with a 180°F ceiling. Alliance's installation manual calls for standard 3/4 inch garden hose couplings, 20 to 120 psi static pressure, and a recommended maximum hot water temperature of 125°F. Those two limits conflict, which is why the plumber, the water heater selection and the machine order have to be settled together.
How big should the water heater be?
Sized from the machines, not from a rule of thumb. IPC 607.1 says that in nonresidential occupancies "hot water shall be supplied for culinary purposes, cleansing, laundry or building maintenance purposes." Heater makers publish commercial laundry sizing tools that ask for the number and capacity of washers, cold water temperature, stored temperature and peak demand period. A. O. Smith's commercial laundry sizing page is built that way. Our restaurant water heater sizing page walks through the same peak-demand logic for another occupancy.
What backflow protection does a laundromat need?
Two layers. At each machine, IPC 406.1 says the supply to an automatic clothes washer "shall be protected against backflow by an air gap that is integral with the machine" or by a backflow preventer installed per Section 608. At the building service, the city can require an assembly. Phoenix City Code 37-144 lists "Laundry and dye works" (air gap or reduced pressure assembly) and "Retail shopping centers and strip malls; retail and industrial shell buildings (when one service supplies more than one tenant)" as requiring a reduced pressure assembly. Mesa's table lists commercial laundries, and commercial buildings where one service connection supplies multiple tenants, as needing a reduced pressure assembly. Most laundromats are strip-center tenants, so check both lines. See which businesses need a backflow assembly for the tenant side.
How do the washers drain?
By standpipe or trench, into a 3-inch or larger branch. IPC 406.2 says washer waste "shall discharge through an air break into a standpipe" or into a laundry sink. The trap and fixture drain for the standpipe must be at least 2 inches, and that drain connects to a 3-inch or larger fixture branch or stack. Section 802.4.3 says standpipes "shall extend not less than 18 inches" and not more than 42 inches above the trap weir. Washers that discharge by gravity "shall be permitted to drain to a waste receptor or an approved trench drain." Table 709.1 counts a commercial washer as 3 drainage fixture units with a 2-inch trap, which feeds the drain sizing for the whole room.
Alliance's manual adds that the drain system must be vented to prevent an air lock or siphoning, and that applies to the standpipes and branches you design.
Does a laundromat need floor drains?
Yes. IPC 413.4 says that in public coin-operated laundries the rooms with automatic washers "shall be provided with floor drains located to readily drain the entire floor area," and each drain needs an outlet of not less than 3 inches. A burst hose or an overflowing machine is the reason. Keep the trap seals alive, because a dry floor drain trap is an odor path; see trap primers for commercial floor drains.
Do you need a lint interceptor?
Almost certainly. IPC 1003.6 requires clothes washers other than the exempt cases to discharge through an interceptor with a removable basket or similar device. The details, exemptions and city add-ons are on our commercial laundry lint interceptor page. Phoenix's pretreatment due diligence guide lists laundries among the businesses that need wastewater pretreatment devices, and says construction plans for businesses discharging process wastewater into the sanitary sewer must be reviewed.
What this means for your plans
- 1Choose the washer line first, then match supply, pressure and hot water temperature to its manual.
- 2Draw hot and cold mains for peak, not average, demand.
- 3Show an air gap or backflow preventer for each washer and check the service-level assembly with the city.
- 4Show standpipes or trench drains, 3-inch branches, venting, floor drains and the lint interceptor.
- 5If you are replacing machines later, read can a laundromat replace washers without changing the drain system.
HQ is licensed and insured and gives free estimates with upfront pricing for commercial plumbing. We can lay out supply and drain rough-in with your equipment spec sheets in hand.