--- title: "Water, drain and exhaust rough-ins: what must be in the wall before the appliance" description: "Supply stubs, drain heights, air gaps, standpipes, laundry exhaust openings and hood ducts: the rough-in figures the installation instructions give, and why…" url: "https://applianceinstallation.center/guides/water-drain-and-exhaust-rough-ins/" date_modified: "2026-09-26" --- Get the space ready # Water, drain and exhaust rough-ins: what must be in the wall before the appliance An appliance rough-in is the plumbing and ducting set before installation: a hot water stub and 1 1/2-inch cabinet holes for dish care, a cold line in the maker's tubing for an ice maker, laundry valves within 4 feet and a standpipe at least 39 inches high, a 4-inch rigid metal laundry exhaust within the length chart, and a full-size metal duct to the outside for a hood. By [ApplianceInstallation.center technical team](https://applianceinstallation.center/authors/technical-team/) Published September 26, 2026 ## At a glance. Before an appliance arrives, the house has to meet it halfway: a water stub where the drawing puts it, a drain at the right height, a hole in the outside wall for the exhaust. Those are set while walls and cabinets are still open, and each one is far cheaper to place correctly than to move once the finishes are in. Read the whole guide ### Dish care water Hot, 120 to 140°F, 20 to 120 psi GE: line reaching 19 inches out from the rear wall. ### Dish care drain Air gap if the tee is under 18 in. GE: hose no longer than 12 feet. ### Laundry standpipe At least 39 inches high Whirlpool: lower and the tub drains by gravity. ### Laundry exhaust 4-inch rigid metal, no screen GE: 90 ft straight, 60 ft with one elbow on normal-vent models. In this guide 1. What a rough-in is, and why it comes first 2. Water supply stubs for dish care, cold storage and laundry 3. Drains: the air gap, the high loop and the standpipe 4. Laundry exhaust: where the wall opening goes 5. Hood ducting and make-up air 6. Step by step 7. Questions ## What a rough-in is, and why it comes first A rough-in is everything behind the finished surfaces that an appliance plugs into: supply pipes and their valves, drain pipes and their fittings, ducts and the openings where they leave the house. The installation instructions show where each one should come out of the wall or floor, usually as shaded zones on a drawing, and the appliance is designed so that its own hoses and connectors reach those zones and no farther. Getting the appliance rough-in right is mostly a matter of timing. Once drywall, tile and cabinets are in, moving a drain six inches means opening finished work. Walking the rough-in with the installation instructions in hand, before insulation goes up, catches most problems while they are still inexpensive. ### One drawing per appliance on site Print the rough-in page for every appliance and tape it near its future opening. Plumbers, electricians and duct installers work in sequence, and each one placing their part from the same sheet is how the water stub, the receptacle and the drain end up where the appliance expects them. ## Water supply stubs for dish care, cold storage and laundry GE's built-in dish care machines take hot water at 120 to 140°F and 20 to 120 psi through 3/8-inch copper tubing or a braided hose, from a shutoff in an accessible place such as under the sink. The line enters through a 1 1/2-inch hole in the zone the drawing shows and must reach at least 19 inches forward from the rear wall so it can be connected at the front. GE also asks for the line to be flushed before connection to clear out debris. Cold storage lines are more particular than people expect. True's built-ins with ice makers want a cold potable supply only, of 1/4-inch PEX with 30 to 100 psi, and say copper is not recommended. The tubing named on the spec sheet, not a plumber's habit, is what should be roughed in. Laundry is simpler: Whirlpool wants hot and cold valves within 4 feet of the machine's fill valves, at 20 to 100 psi, with the water heater at 120°F. - Dish care: hot supply, shutoff under the sink, line stubbed to reach 19 inches forward - Ice maker: cold potable water only, in the tubing the maker specifies, purged before connection - Laundry: hot and cold valves within 4 feet, both open for every cycle - Every appliance: its own shutoff, reachable without moving the appliance Source: [GE Appliances — Installation instructions, built-in dishwasher](https://products-salsify.geappliances.com/image/upload/s--yxlKQraa--/4e08089748bc59f01329d93f1d3a0456e6018299.pdf) — Hot water 120–140°F at 20–120 psi via 3/8 in. copper or braided hose; accessible shutoff; 1 1/2 in. holes; line 19 in. forward; flush the line; drain hose 12 ft maximum, 72 in. maximum height; air gap if code requires or the tee is under 18 in.; remove the disposer plug; [True Residential — 42/48 built-in installation manual](https://true-residential.com/wp-content/uploads/2020/01/848062-TR-42-48-C-Install-Manual_REV_C_EN.pdf) — Potable cold water only, 1/4 in. PEX, copper not recommended, 30–100 psi; purge the line before connection; [Whirlpool — Electrical supply needed for a washer](https://producthelp.whirlpool.com/Laundry/Washers/Product_Info/Washer_Installation_Support/Electrical_Supply_Needed_for_a_Washer) — Hot and cold faucets within 4 feet of the fill valves at 20–100 psi; water heater at 120°F Close on a laundry box in a wall with hot and cold valves and a drain opening. ## Drains: the air gap, the high loop and the standpipe A dish care drain has limits on distance and height. GE keeps the drain hose to 12 feet or less and the connection no higher than 72 inches above the bottom of the machine. If local code calls for an air gap, or the waste tee or disposer inlet is less than 18 inches above the floor, an air gap is required; otherwise a high drain loop, fastened to the cabinet with the supplied hanger, is acceptable. Whirlpool sets its own high-loop minimum at 20 inches from the floor. A laundry machine needs a standpipe or laundry tub. Whirlpool wants the top of the standpipe at least 39 inches above the floor, since below that water flows out of the tub by gravity, and the drain hose reaching more than 4.5 inches inside it without being sealed in with tape. LG fixes the hose in its elbow bracket within 4 inches of its end and straps it in place so it cannot jump out. ### The knockout plug in a new disposer A new disposer comes with a plug sealing its dish care inlet. Whirlpool and GE both flag it: the plug must be knocked in and removed before the drain hose is clamped on, or the machine cannot drain at all. It is one of the most common reasons a newly installed machine leaves water in the tub. Source: [GE Appliances — Installation instructions, built-in dishwasher](https://products-salsify.geappliances.com/image/upload/s--yxlKQraa--/4e08089748bc59f01329d93f1d3a0456e6018299.pdf) — Hot water 120–140°F at 20–120 psi via 3/8 in. copper or braided hose; accessible shutoff; 1 1/2 in. holes; line 19 in. forward; flush the line; drain hose 12 ft maximum, 72 in. maximum height; air gap if code requires or the tee is under 18 in.; remove the disposer plug; [Whirlpool — Checking the drain loop height](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Product_Assistance/Checking_the_Drain_Loop_Height) — High loop at least 20 inches from the floor, or use an air gap; [Whirlpool — Connecting dishwasher drain to garbage disposal](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Installation_Support/Connecting_Dishwasher_Drain_to_Garbage_Disposal) — Knock the plug into the disposer and remove it before attaching the drain hose; [Whirlpool — Front load washer installation checklist](https://producthelp.whirlpool.com/Laundry/Washers/Product_Info/Washer_Installation_Support/Front_Load_Washer_Installation_Checklist) — Standpipe top at least 39 inches from the floor; hose more than 4.5 inches into the pipe; not sealed with tape; [LG Electronics — Washer owner's manual (WM4080)](https://media.us.lg.com/m/12df7154cf356724/original/WM4080_2023_Owners-Manual_Washer_Eng.pdf) — Elbow bracket within 4 inches of the hose end; secure with the tie strap ## Laundry exhaust: where the wall opening goes The exhaust run is mostly decided by where the hole in the outside wall is cut. GE's instructions call for 4-inch rigid metal duct to the outdoors, no plastic or foil, and no screen in or over the duct. Its chart for normal-vent models allows 90 feet of rigid metal with no elbows, 60 feet with one and 45 with two, less with some hood styles, while long-vent models reach up to 200 feet. Elbows count against that length. GE treats any bend sharper than 45 degrees as a 90-degree elbow, two 45-degree bends as one 90, and a side-exhaust conversion as one extra elbow, and counts the transition duct in the total. Whirlpool wants the exhaust hood at least 12 inches above the ground and anything that could block it. - Wall opening placed for the straightest, shortest run to the outside - 4-inch rigid metal duct, with every elbow counted against the chart - No screen at the hood, and the hood at least 12 inches above grade - Room behind the machine for the transition duct without crushing it Source: [GE Appliances — Dryer owner's manual and installation instructions (49-3000386)](https://images.salsify.com/image/upload/s--xjgUHYwo--/adddbe062f46e3a5cfe1dabf3a195badcac0609e.pdf) — 4 in. rigid metal to the outdoors, no screen; 90/60/45 ft for 0/1/2 elbows on normal-vent models, up to 200 ft on long-vent; elbow counting rules including the transition duct; [Whirlpool — How to check your dryer venting system](https://producthelp.whirlpool.com/Laundry/Dryers/Product_Info/Dryer_Product_Assistance/How_to_Check_Venting) — Exhaust hood at least 12 inches from the ground or obstructions ## Hood ducting and make-up air A ducted hood is only as good as its duct. Vent-A-Hood's instructions require smooth galvanized metal duct to the outdoors, never flexible or corrugated, never reduced below the blower's size, with a wall louver or roof jack on every run. Its single-blower models need 6-inch round duct or its 28-square-inch equivalent and its dual-blower models 8-inch round. It counts each 90-degree elbow as 5 feet of duct and adds an inch of diameter for every 10 feet beyond 20. An over-the-range microwave with an exhaust fan follows its own figures. Sharp's connects to standard 3 1/4 by 10 inch rectangular duct, or 6-inch round through an adapter, with a total equivalent length under 140 feet; a rear exhaust must line up with the space between wall studs, which is far easier to plan before the wall is closed. ### Make-up air in a tight house A strong hood pulls air out of the house, and that air has to come from somewhere. Vent-A-Hood cites the ASHRAE residential ventilation standard, which limits total exhaust fans to 15 CFM per 100 square feet of living space unless a backdraft test is done or make-up air is provided, and warns that fuel-burning equipment needs enough air to vent properly. Ask an HVAC contractor about make-up air before choosing a large blower. Source: [Vent-A-Hood — Wall mount hood installation instructions](https://www.ventahood.com/installpdfs/wall%20mount%20range%20hood%20installation%20instructions.pdf) — Smooth galvanized metal duct to the outdoors, never reduced or flexible; 6 in. round single blower, 8 in. dual; 90° elbow = 5 ft; +1 in. diameter per 10 ft over 20 ft; ASHRAE 62.2 limit of 15 CFM per 100 sq ft without a backdraft test or make-up air; [Sharp — Over-the-range microwave installation instructions (R-1881LSY)](https://files.sharpusa.com/Downloads/ForHome/HomeAppliances/MicrowaveOvens/InstallationGuides/R-1881LSY_IG_EN_061217.pdf) — 3 1/4 x 10 in. rectangular or 6 in. round duct; total equivalent length under 140 ft; rear exhaust aligned between studs ## Where to stop Cutting into supply or drain pipes, adding a valve, installing an air gap, cutting a duct opening through an exterior wall or roof and running new gas pipe are jobs for the plumber, duct installer or installer, often under a permit; book a site check. An owner should never cap or extend a drain in a way that removes the air gap or the loop, and never vent a laundry machine or hood into an attic, wall cavity or crawl space. Written by [ApplianceInstallation.center technical team](https://applianceinstallation.center/authors/technical-team/). Installers who fit new household appliances, writing from real openings and hookups and each maker's installation instructions. Sources: [GE Appliances — Installation instructions, built-in dishwasher](https://products-salsify.geappliances.com/image/upload/s--yxlKQraa--/4e08089748bc59f01329d93f1d3a0456e6018299.pdf) · [True Residential — 42/48 built-in installation manual](https://true-residential.com/wp-content/uploads/2020/01/848062-TR-42-48-C-Install-Manual_REV_C_EN.pdf) · [Whirlpool — Electrical supply needed for a washer](https://producthelp.whirlpool.com/Laundry/Washers/Product_Info/Washer_Installation_Support/Electrical_Supply_Needed_for_a_Washer) · [Whirlpool — Checking the drain loop height](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Product_Assistance/Checking_the_Drain_Loop_Height) · [Whirlpool — Connecting dishwasher drain to garbage disposal](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Installation_Support/Connecting_Dishwasher_Drain_to_Garbage_Disposal) · [Whirlpool — Front load washer installation checklist](https://producthelp.whirlpool.com/Laundry/Washers/Product_Info/Washer_Installation_Support/Front_Load_Washer_Installation_Checklist) · [LG Electronics — Washer owner's manual (WM4080)](https://media.us.lg.com/m/12df7154cf356724/original/WM4080_2023_Owners-Manual_Washer_Eng.pdf) · [GE Appliances — Dryer owner's manual and installation instructions (49-3000386)](https://images.salsify.com/image/upload/s--xjgUHYwo--/adddbe062f46e3a5cfe1dabf3a195badcac0609e.pdf) · [Whirlpool — How to check your dryer venting system](https://producthelp.whirlpool.com/Laundry/Dryers/Product_Info/Dryer_Product_Assistance/How_to_Check_Venting) · [Vent-A-Hood — Wall mount hood installation instructions](https://www.ventahood.com/installpdfs/wall%20mount%20range%20hood%20installation%20instructions.pdf) · [Sharp — Over-the-range microwave installation instructions (R-1881LSY)](https://files.sharpusa.com/Downloads/ForHome/HomeAppliances/MicrowaveOvens/InstallationGuides/R-1881LSY_IG_EN_061217.pdf) ## Step by step. Four steps, in the order worth doing them. 01 ### Collect the drawings Print the rough-in page from each appliance's installation instructions. 02 ### Mark the zones Outline the water, drain, gas and electrical zones on the open studs and floor. 03 ### Check heights Measure the waste tee, the standpipe and the exhaust opening against the figures before walls close. 04 ### Count the run Add up straight duct and elbows for the laundry exhaust and hood duct against each maker's limit. For the heart of your home. ## Questions owners ask. ### Does every dish care installation need an air gap? Not always. GE requires one where local codes call for it or where the waste tee or disposer inlet is less than 18 inches above the floor; otherwise a high drain loop is acceptable. ### Can an ice maker line be tied into the hot water pipe that feeds the sink? No. True says to connect only to a cold potable supply and never to hot water. ### What is the longest laundry exhaust run a maker allows? It depends on the maker's chart. GE allows 90 feet of 4-inch rigid metal with no elbows on normal-vent models and less for each elbow and some hood styles. ### Is a flexible duct acceptable above a hood if it is short? Vent-A-Hood says no: only smooth galvanized metal duct, because flexible and corrugated duct restrict airflow and reduce performance. ## The problems behind it. Each has a page of its own: what it usually means and the causes in the order worth checking. [All 17 problems](https://applianceinstallation.center/problems/) Problem ### Drain Backing Up After an Install: Plug, Loop and Standpipe 6 causes, cheapest first Hazard after a hookup ### Laundry Exhaust Crushed, Loose or Blowing Into the Room 6 causes, cheapest first Problem ### Hood Not Drawing Smoke: Duct Size, Damper and Makeup Air 6 causes, cheapest first Problem ### Water Hammer After a Hookup: Banging Pipes When a Valve Shuts 6 causes, cheapest first ## When it needs a technician. The installations on the right are where this guide ends when the checks do not settle it. ### Water supply and shutoff connection New supply lines from a working quarter-turn stop to each water appliance, tested under pressure. ### Drain and air gap connection Drain hoses run through a high loop, air gap or standpipe, clamped and proved on a first drain. ### Laundry exhaust run installation A metal exhaust path from a new dryer to the outdoors: short transition, taped joints, a working hood. ### Hood ducting and fan installation A hood hung and ducted outdoors at full size, with a working damper and makeup air planned. ## More in get the space ready. Everything worth having ready before delivery: an opening that matches the maker's cutout drawing, a clear path through doors, stairs and floors, and the water, drain and exhaust rough-ins the new appliance will need. [The whole section](https://applianceinstallation.center/guides/installation-and-setup/) The opening, the path in and the rough-ins ### Cutout dimensions and the spec sheet: reading the numbers before cabinets are built Product size, opening size and the clearances above and beside the appliance are three different sets of figures. How to read them on a spec sheet before anyone cuts a cabinet. The opening, the path in and the rough-ins ### The delivery path: doors, stairs and floors between the truck and the opening Every doorway, turn and stair the appliance must pass, the weight the floor has to carry, what to inspect before the crew leaves, and how the old unit should leave the house. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Water, drain and exhaust rough-ins: what must be in the wall before the appliance](https://applianceinstallation.center/guides/water-drain-and-exhaust-rough-ins/)** **[Book a visit with ApplianceInstallation.center](https://applianceinstallation.center/schedule/)**