--- title: "Laundry venting and makeup air for tumblers: duct runs, shared mains and the lint schedule" description: "Why every tumbler needs air in as well as out, Dexter's duct lengths, elbows and outlet rules, joining a row into one main, dry-cleaning vapors, and the…" url: "https://commercialappliancerepair.center/guides/laundry-venting-and-makeup-air/" date_modified: "2026-09-26" --- Installation and setup # Laundry venting and makeup air for tumblers: duct runs, shared mains and the lint schedule Commercial dryer venting follows the maker's installation manual: smooth metal duct of the stated diameter run outdoors, as short as the manual allows, joints lapped in the direction of flow, no screen on the outlet, and makeup air openings sized for every tumbler in the room. Dexter's stacked 50-pound models, for example, each need 1½ square feet of net opening to the outside. By [CommercialApplianceRepair.center technical team](https://commercialappliancerepair.center/authors/technical-team/) Published September 26, 2026 ## At a glance. A tumbler is an air pump as much as a heater: every cycle pulls room air across the burner or elements, through the load and out through the duct. When the duct is too long or the room cannot replace that air, drying slows, the high-limit starts cycling the heat off, and lint settles where it can burn. Read the whole guide ### Makeup air, stacked 50 lb 1,000 CFM and 1½ sq ft of opening Net free area after grilles and louvers, per Dexter's DDAD50KC manual. ### Duct run, 80 lb single 20 ft of 8-inch duct, two elbows Dexter takes 2 feet off for each extra elbow and allows four at most. ### Outlet No screen, 24 inches clear A hood with a hinged damper or a downturned end keeps weather out instead. ### Duct inspection Once a year, to the outlet On Dexter's preventive maintenance list; the lint screen is daily. In this guide 1. Air in, air out: why tumblers need both 2. The exhaust run from collar to outlet 3. One main duct for a row of machines 4. What the intake air carries in with it 5. The lint schedule that keeps the duct clear 6. Questions ## Air in, air out: why tumblers need both Each machine draws air from the room, heats it, drives it through the tumbling load and throws it outside with the moisture and lint it picked up. Whatever leaves has to be replaced. Dexter's manual for its DDAD50KC stacked models puts the figure at 500 cubic feet per minute for each drum, 1,000 for the pair, and its DTCK80 single-pocket models at 1,200. Dexter lists what happens when the exhaust is restricted: slow drying, excessive heat and lint in the room. It also explains the less obvious symptom, a high-limit thermostat that keeps cutting the burners off, which makes the machine look like it has a heating problem when the real trouble is the air path. ### Makeup air is measured as net free area The opening Dexter asks for, 1½ square feet per stacked 50-pound machine and 1¼ per 80-pound single, is net effective area. Screens, grilles and louvers block part of an opening, so a louver that looks big enough may deliver far less; Dexter tells installers to ask the grille supplier for its free-area figure. It also wants multiple openings, placed far enough from the machines to give every intake an even share of the air. Source: [Dexter — DDAD50KC Series stacked models operator's and installation manual (8514-141-001)](https://web.archive.org/web/2020/http://www.dexter.com/laundry/download/commercial/owners_and_installation_manual_T-50x2.pdf) — 500 CFM per drum and 1,000 per machine with 1½ sq ft of net makeup opening; restricted exhaust causes slow drying, excess heat, lint in the room and high-limit cycling; 8-inch duct, 14 feet with two elbows per drum; lapped joints, 1-inch clearance, wall sleeve, damper hood, 24-inch clear outlet, never a screen, cone rain cap, never a chimney; branches at 45 degrees and an inspection door on a main; keep makeup air away from dry cleaners; daily, monthly, semiannual and annual lint tasks; [Dexter — DTCK80, DCTD80KC and DCWD80KC Series owner's manual (8514-052-001E)](https://web.archive.org/web/2020/http://www.dexter.com:80/laundry/download/commercial/Owners_Manual_dryers_d80.pdf) — 1,200 CFM and 1.25 sq ft of net makeup opening per machine; 20 feet of 8-inch duct with two elbows, minus 2 feet per extra elbow, four elbows at most ## The exhaust run from collar to outlet In commercial dryer venting, every foot of pipe and every elbow costs the blower some of its airflow. Dexter's stacked models take an 8-inch round duct, and the manual recommends no more than 14 feet of straight pipe with two right-angle elbows for each drum. Its 80-pound singles allow 20 feet with two elbows, minus 2 feet for each elbow beyond that and no more than four in all. The inside has to be smooth, because, as Dexter puts it, rough surfaces collect lint that eventually clogs the duct. The outlet end has its own rules. Wind and rain are kept out by a hood with a hinged damper or by turning the pipe end downward, and the outlet stays at least 24 inches from anything that would block the air. A duct through a roof carries the same length limits as one through a wall and needs a cone-type rain cap that will not clog. - Smooth metal pipe of the diameter on the data plate or in the manual - Each joint lapped so the upstream section slides inside the next one downstream - At least 1 inch of clearance between the duct and combustible material - A metal sleeve wherever the duct passes through a wall - Never a protective screen over the outlet - Never vented into a chimney or under the building Source: [Dexter — DDAD50KC Series stacked models operator's and installation manual (8514-141-001)](https://web.archive.org/web/2020/http://www.dexter.com/laundry/download/commercial/owners_and_installation_manual_T-50x2.pdf) — 500 CFM per drum and 1,000 per machine with 1½ sq ft of net makeup opening; restricted exhaust causes slow drying, excess heat, lint in the room and high-limit cycling; 8-inch duct, 14 feet with two elbows per drum; lapped joints, 1-inch clearance, wall sleeve, damper hood, 24-inch clear outlet, never a screen, cone rain cap, never a chimney; branches at 45 degrees and an inspection door on a main; keep makeup air away from dry cleaners; daily, monthly, semiannual and annual lint tasks; [Dexter — DTCK80, DCTD80KC and DCWD80KC Series owner's manual (8514-052-001E)](https://web.archive.org/web/2020/http://www.dexter.com:80/laundry/download/commercial/Owners_Manual_dryers_d80.pdf) — 1,200 CFM and 1.25 sq ft of net makeup opening per machine; 20 feet of 8-inch duct with two elbows, minus 2 feet per extra elbow, four elbows at most Close on the round exhaust ducts behind a row of commercial tumblers. ## One main duct for a row of machines Dexter recommends a separate duct for each machine. Where a row has to share a main discharge duct, each branch enters the main at a 45-degree angle pointing the way the air flows, from the side or the bottom, and never at a right angle, which would push one machine's air against another's. The main grows in diameter as each branch joins, and keeps its full size from the last machine all the way to the outlet. Getting the size right cuts both ways. Dexter points out that a duct too small restricts airflow, while one too large slows the air down, and both let lint drop out and build up inside. The manual asks for an inspection door so the main can be cleaned out on a schedule. ### Adding a machine to an existing row One more tumbler on a shared main changes the airflow for every machine already on it, and it adds to the makeup air the room must supply. The installer rechecks the main's diameter at the new branch, the total equivalent length for the farthest machine, and the free area of the room's openings before the new unit is fired. Source: [Dexter — DDAD50KC Series stacked models operator's and installation manual (8514-141-001)](https://web.archive.org/web/2020/http://www.dexter.com/laundry/download/commercial/owners_and_installation_manual_T-50x2.pdf) — 500 CFM per drum and 1,000 per machine with 1½ sq ft of net makeup opening; restricted exhaust causes slow drying, excess heat, lint in the room and high-limit cycling; 8-inch duct, 14 feet with two elbows per drum; lapped joints, 1-inch clearance, wall sleeve, damper hood, 24-inch clear outlet, never a screen, cone rain cap, never a chimney; branches at 45 degrees and an inspection door on a main; keep makeup air away from dry cleaners; daily, monthly, semiannual and annual lint tasks ## What the intake air carries in with it A gas tumbler burns the room's air, so anything in that air goes through the flame. Dexter warns that makeup air and room ventilation for its machines must come from sources away from any dry-cleaning equipment. Solvent vapors break down in the gas flame into products corrosive enough to damage the ducts, the machines and the loads inside them. The same manuals ask that nothing obstruct the combustion and ventilation air reaching the machines. In a busy store that means keeping cases of detergent, bagged laundry and carts away from the openings, and never covering a makeup air louver to keep out winter drafts. ### A laundry that shares a wall with a dry cleaner Combined stores and strip-mall neighbors are where solvent and flame meet. Where the makeup air openings sit relative to the dry-cleaning machines, the neighbor's vents and the shared rooftop is worth settling with the installer at the design stage, since moving an opening later means new work through the wall or roof. Source: [Dexter — DDAD50KC Series stacked models operator's and installation manual (8514-141-001)](https://web.archive.org/web/2020/http://www.dexter.com/laundry/download/commercial/owners_and_installation_manual_T-50x2.pdf) — 500 CFM per drum and 1,000 per machine with 1½ sq ft of net makeup opening; restricted exhaust causes slow drying, excess heat, lint in the room and high-limit cycling; 8-inch duct, 14 feet with two elbows per drum; lapped joints, 1-inch clearance, wall sleeve, damper hood, 24-inch clear outlet, never a screen, cone rain cap, never a chimney; branches at 45 degrees and an inspection door on a main; keep makeup air away from dry cleaners; daily, monthly, semiannual and annual lint tasks ## The lint schedule that keeps the duct clear Dexter's preventive maintenance list starts with the lint screen every day, brushed clean and checked for rips. Monthly work goes inside the cabinet, clearing lint from the motor, the controls area and around the burners, which Dexter calls a fire hazard when neglected; that happens with all power disconnected. Once a year the whole duct is inspected and cleaned, from the machine's connection to the exit at the wall or roof. Drying times are the early warning. When loads start needing an extra cycle, the room runs hotter than it used to or lint gathers around the outlet, the duct and the makeup air belong on the next service visit before anyone looks for a failed heating part. - Daily: lint screens brushed clean and checked for tears - Monthly, power off: lint cleared from the motor, controls and burner area - Every six months: lint cleaned from inside the front panel and the burner air ports - Yearly: exhaust duct inspected and cleaned to the outlet Source: [Dexter — DDAD50KC Series stacked models operator's and installation manual (8514-141-001)](https://web.archive.org/web/2020/http://www.dexter.com/laundry/download/commercial/owners_and_installation_manual_T-50x2.pdf) — 500 CFM per drum and 1,000 per machine with 1½ sq ft of net makeup opening; restricted exhaust causes slow drying, excess heat, lint in the room and high-limit cycling; 8-inch duct, 14 feet with two elbows per drum; lapped joints, 1-inch clearance, wall sleeve, damper hood, 24-inch clear outlet, never a screen, cone rain cap, never a chimney; branches at 45 degrees and an inspection door on a main; keep makeup air away from dry cleaners; daily, monthly, semiannual and annual lint tasks ## Where to stop Attendants clean the lint screens and keep the outlet and the makeup air openings clear. Resizing or rerouting a duct, cutting a new opening in a wall or roof, working behind the cabinet near the gas and electrical connections, or cleaning around the burners is work for the installer or a technician with the machine's power and gas shut off; book it when drying times start to creep up. Written by [CommercialApplianceRepair.center technical team](https://commercialappliancerepair.center/authors/technical-team/). Technicians who service restaurant, institutional and laundry equipment, working from site visits, service logs and makers' manuals. Sources: [Dexter — DDAD50KC Series stacked models operator's and installation manual (8514-141-001)](https://web.archive.org/web/2020/http://www.dexter.com/laundry/download/commercial/owners_and_installation_manual_T-50x2.pdf) · [Dexter — DTCK80, DCTD80KC and DCWD80KC Series owner's manual (8514-052-001E)](https://web.archive.org/web/2020/http://www.dexter.com:80/laundry/download/commercial/Owners_Manual_dryers_d80.pdf) For the heart of your home. ## Questions owners ask. ### Can two tumblers share one exhaust duct? Dexter recommends a separate duct for each machine. Where a shared main is needed, branches enter at 45 degrees in the direction of flow and the main is sized for every machine on it. ### Should the outside vent have a screen to keep birds out? No. Dexter says never to put a protective screen over the exhaust outlet, because lint clogs it. A hood with a hinged damper does the job instead. ### Why do loads take longer after a louver was covered for the winter? The room can no longer replace the air the machines exhaust, so less air moves through each load and the high-limit may start cutting the heat. Uncover the opening and keep it clear. ### How often should the exhaust duct be cleaned? Dexter lists a yearly inspection and cleaning of the full run to the outlet. On a shared main, a look through the inspection door shows whether a busy store needs it sooner. ## 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://commercialappliancerepair.center/problems/) Problem ### Commercial Laundry Tumbler Not Heating: Loads Still Damp After a Full Cycle 6 causes, cheapest first Gas, fire, food at risk or water near power ### Restaurant Equipment Burning Smell: Scorched Oil, Hot Wiring or Lint 6 causes, cheapest first Gas, fire, food at risk or water near power ### Commercial Kitchen Gas Smell Along the Cooking Line: Clear the Room First 6 causes, cheapest first ## When it needs a technician. The repairs on the right are where this guide ends when the checks do not settle it. ### Commercial laundry machine repair Coin, card and on-premise laundry machines and tumblers: door locks, bearings, inverters, burners and payment hardware. ### Commercial preventive maintenance plan Scheduled visits across cold, cooking, warewashing and laundry: coils, gaskets, calibration, gas checks and a written log. ### Commercial appliance diagnostic visit One visit finding why a cooler, fryer, oven, dish machine or laundry machine stopped earning its keep. ## More in installation and setup. Air around a condensing unit, the gas, the voltage and the phase a unit was built for, water treatment and drains for dish machines and combis, and the hood and clearances a cooking line needs. [The whole section](https://commercialappliancerepair.center/guides/installation-and-setup/) Clearances, utilities, drains and airflow ### Gas quick-disconnects, hoses and restraint cables on caster-mounted cooking equipment The ANSI standards the makers name, why the restraint takes the pull instead of the hose, cleaning night and the fire system above, and the signs a connector needs the installer. Clearances, utilities, drains and airflow ### Space and airflow around rooftop condensing units: widths, pits, screen walls and exhaust fans Heatcraft's one-width rule, pits and decorative fences, units side by side, grease from the hood fan landing on the coil, roof structure and noise, and what a manager can watch from below. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Laundry venting and makeup air for tumblers: duct runs, shared mains and the lint schedule](https://commercialappliancerepair.center/guides/laundry-venting-and-makeup-air/)** **[Book a visit with CommercialApplianceRepair.center](https://commercialappliancerepair.center/schedule/)**