It's the only move a villain can make that's stupider than Locking MacGyver in the Store Cupboard (or any room with a bed). When heroes find themselves trapped in a room with all doors and windows locked, the quickest exit is always through the ventilation duct. Air vents also work excellently in reverse for breaking in and infiltrating a facility.
Openings are within reach, covers require little effort to remove, the ducts themselves can support the weight of a person and are wide enough in diameter to allow an adult to pass through, there are no internal obstacles except for the occasional Deadly Rotary Fan blocking the branching corridors, they are free of normal sheet metal's dangerously sharp edges, they are totally soundproof, there are no security cameras, and there's never a lack of light or chance of getting lost unless the plot calls for it.
And the escapee always emerges without having picked up so much as a speck of dust.
A smart villain would have smaller air ducts, post guards around the openings, or line their ducts with barbed wire and broken glass. It even appears near the top of the Evil Overlord List.
This is practically a Discredited Trope by now, and requires some effort to justify if it's to be used seriously. Despite that, it does happen once in a while in real life. Frank Morris and his accomplices escaped from Alcatraz using the large ventilation duct that led them to the roof. And that leads to knowing that large industrial, commercial and construction complexes need to have enough air flow to manage their needs (like hot equipment or extremely deep locations for personnel use), which often requires a large ventilation system. It's not practical in general use though, still, as grates bolted in place still block your entrance and getting towards office space will shrink the vents.
Some large universities (MIT and Caltech in particular) have longstanding "steam tunnel spelunkers" clubs, who often use air ducts (among other things) for exploring, getting around campus quickly, or pulling pranks. Readers of this trope should be advised that this is extremely dangerous, not to mention illegal steam tunnels are usually hot, cramped, and frequently criss-crossed by scalding-hot piping, and explorers face trespassing charges and possible academic sanctions if they're discovered withinnote . Disney, meanwhile, has taken the concept of utility tunnels and turned them into the Utilidor system used at their parks, which allows staff to quickly move from one area to another without ever needing to break the suspension of disbelief by wandering about in their uniform on the surface.
Most Real Life attempts to sneak in or out via air duct aren't very successful, since people tend to be fairly large and ducts tend to be fairly small, plus the fact that air can bend at ninety degree angles and fit through grates much more readily. There have been numerous cases where enterprising criminals have attempted to rob a store by sneaking through the ducts and end up getting stuck. The usual ending is the embarrassed criminal being either pulled or cut out of the duct by the fire department and then promptly handed over to the authorities. That is if they don't crash through the ceiling when the vent gives way under their weight.
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- Happy Heroes: In episode 8, Big M. and Little M. crawl through an air vent to reach the heroes and make them sick with their cold.
- Lampshaded in the Big Finish Doctor Who audio adventure "The Apocalypse Element".
Evelyn: There must be some other way. An inspection hatch, or even, God help us, a ventilation shaft!
- Played straight in the BBC Radio 4 adaptation of the Raffles story "The Gift of the Emperor". Raffles uses the cruise ship's ventilation system to sneak between rooms. The book (which was written in the nineteenth century) employs a more era-appropriate chimney-drop.
- Scarecrow escaped Arkham Asylum this way. Justified in that this villain has always been a skinny britches. And it's Arkham Asylum.
- Used again in the 1980s Frank Miller envisioning of Batman. True, this time it was an arranged "escape" — with both Batman and Commissioner Gordon in on the act of breaking a villain out of an ordinary holding cell. However, this time the prisoner is the hulking Mutant leader, a man built enough to take on Batman in hand-to-hand combat. (The breakout was so that Batman could have a rematch, after also arranging for the entire Mutant gang to be on hand to watch their leader get taught a lesson in messing with the Batman.)
- In Robin Series Damain worked his way to the heart of the Batcave using the air vents when he was trying to escape from his grandfather. He wasn't able to enter the vents until he'd already made it into the cave and past layers of security, and it wasn't sneaky at all as Tim was well aware of his location and waiting for him when he exited.
- Used in a Bash Street Kids strip in The Beano which saw Fatty, Plug and Smiffy crawl into a vent in an attempt to steal a key off Teacher.
- Discussed by Catwoman, who explains that extra and unnecessarily large vents and crawlspaces are common in Gotham as a result of the widespread corruption that allows contractors to get paid for extra construction on municipal buildings, then further cautions that most of these are undependable and poorly made because they're just there to justify extra budget allocations and the contractors weren't concerned with their use and upkeep.
- Played with in Diabolik: Some houses may have or have not vents sufficiently large, resulting in Diabolik and Eva (extremely agile people) either climbing in themselves or using a remote-controlled robot to reach the safe or vault.
- The series being what it is, one of Diabolik's targets put together a Diabolik-proof vault, whose security measures included vents too small for Diabolik and Eva and an always active jammer in case someone tried with a remote-controlled robot. Thus you can understand how surprised were Diabolik and Ginko when someone still stole from the vault... At least until Diabolik found out it had been the owner's daughter, a very intelligent child who wanted her father's attention.
- Kei tries this in The Dirty Pair series Biohazard. But she gets stuck when her full, child-bearing hips won't fit. Mmmm. It's a Shout-Out to one of the TV episodes. Also contains Yuri's wonderful 4th-wall-leaning/Lampshade Hanging from her outside POV: "Been hitting the cheesecake a little too hard, hmm?"
- In Dreamkeepers, Namah and Mace (and Whip) are both partial to this trope.
- Reed Richards of the Fantastic Four does this now and again as well. Justified in that his powers are to stretch his body to any length, and width.
- In Flare, Raven Gold the party crasher uses one to sneak into Max Krueger's office toward the bottom of this page.
- Subverted in the IDW continuation of G.I. Joe: A Real American Hero. Bombstrike is captured by the Red Shadows and imprisoned in their research facility in Olliestan. When the guards notice through the vision panel in the door that her cell appears to be empty, they throw in a flash-bang grenade before entering (in case she's hiding just out of view from the peephole), only to find the cell is empty and the grate over the air vent is dislodged. The guards do question how she fit through there, but run off to raise the alert, leaving the cell door wide open. Once it's all clear, Bombstrike emerges from above the ceiling tiles in the cell and makes her way out through the corridor.
- In the fourth issue of Gotham City Garage, Supergirl, Nightwing and Catwoman crawl into a vent to break into a secret facility belonging to Lex Luthor.
- Green Lantern: The Lost Army: B'dg crawls through the light pirate's prison's ventilation system to locate the Lanterns' stolen rings and destroy the electronics needed to keep the force field doors up.
- Mickey Mouse Comic Universe:
- In Mickey Mouse and the Chirikawa Necklace, Mickey and Atomo Bleep-Bleep escape a deathtrap through an air vent. May be justified in that they are very small, especially compared to the dogfaces that inhabit the Elaborate Underground Base.
- Mercilessly parodied in an Italian story: in a show they're acting in, Mickey, Goofy and O'Hara infiltrate the starship of the villain this way and encounter a hero going in the opposite direction to save a princess, two monsters, and the President of the United States ("He was just passing through").
- Ms. Tree makes this escape as part of her "Die Hard" on an X plot in the "New Year's Evil" story.
- Subverted in "Earthquake", an issue of Paperinik New Adventures: Paperinik must get around a closed door. Being Genre Savvy, he tries to go into an airvent, remarking: "This always works in the movies!" Being a Pint-Sized Powerhouse, he can crawl in, but his large shield gets stuck.
- An example of a villain using this trope is found in Marvel's 1990s series Sleepwalker, when Serial Killer Jeremy Roscoe, after freeing himself from his restraints, climbs into the ducts to escape the prison hospital where he was being held. Probably not as bad as some of the other examples, since by that time the alarms were already activated and Roscoe's only concern was getting out by the fastest route possible.
- Spider-Man does this every now and again. In an interesting variation, however, he usually does it when he's breaking into a place, rather than trying to escape.
- Averted in Y: The Last Man when Agent 355 and Yorick are breaking into a hotel in Sydney (surrounded by barbed wire and armed security due to the increase in drug-related crime After the End).
Agent 355: You said we'd be able to use the air conditioning vents. They're six inches by four inches.
Yorick: Yeah, well, I overestimated the amount of... air this place might need...
- In a Dilbert strip, Alice tells naive intern Asok, "You must climb through the Jeffries tubes to reach the furnace before it fries us all!" He gets stuck half-way in, but that was her plan: "Today, Asok learns that life is not like Star Trek." With Asok's lower body hanging out of the vent, Alice puts up a sign that reads "Spank the Intern $.50".
- Similarly, the boss has to hide in the ducts when his security clearance is revoked. He gets stuck and is presumed dead, resulting in the construction of a 'totally cool device to increase the duct pressure and propel his carcass into the stratosphere'.
- In a series of Get Fuzzy strips, Bucky tried this tactic to reach the ferret in the next apartment. While he fit fine (because he's a cat) he ended up getting lost and having to call for help... and Satchel mistook the voice coming out of the walls for God. Hilarity Ensues.
- All Dogs Go to Heaven has Charlie Barkin sneak around Carface's casino by moving through the air vents. Charlie succeeds in fishing The Woobie Anne Marie out of her compartment through these vents. Justified, because Charlie is a dog moving around in human-built ductwork, and Anne Marie is a child.
- Subverted in Ed, Edd n Eddy's "Big Picture Show". Taking refuge in Eddy's Brother's room, the Eds try to get out the window. It's bricked in, as shown in a previous episode. ("My brother's a whiz at laying bricks.") While Edd tries to find another way out, he trips over a rug, revealing a heating duct. Eddy quickly pries open the grate, jumps in, and... more bricks. Then Ed finds the "In Case Of Movie Break Glass" case.
- Lilo & Stitch: This is how Stitch escapes from the prisoner bay after breaking out of his cell. Justified because he's small and fast, and all the guards know he's there, they just couldn't shoot him in time.
- The Secret of NIMH carries this over from the book it's based on. The rats make it out fine, however all but two of the mice are blown away to their deaths.
- In Sky Blue, Shua flees Ecoban through the air vents after going through the Absurdly Spacious Sewer system.
- Done by Trig in Starship Troopers: Invasion, where she has to strip out of her power armor to get into the vent. She also mentions that Bugspray would never fit when he wants to go with her.
- Lampshaded near the start of Titan A.E. when Korso tells Cale to head for the vents. Cale responds sarcastically that no one would think to look for them there.
- Toy Story and Toy Story 2. Naturally, ducts are much more convenient when you're eight inches tall.
- Wallace & Gromit's The Wrong Trousers has air ducts to a museum big enough to stand in. They were realistically loud though, insofar as a pair of remote-controlled, vacuum-soled robotic trousers can be realistic.
- Episode 1 of The Orbiting Human Circus (of the Air) opens with protagonist Julian the Janitor's personal Interactive Narrator describing Julian having managed to get backstage by holing up in a heating duct, preparing to sneak into the eponymous radio show's ballroom studio for the third time in a week.
- Used to escape a dead-end in Survival of the Fittest by John Sheppard, Vera Lang and Kyrie Joseph, as killer Harry Tsai was hot on their heels and it was the only way out of the building they had run inside.
- Shelton and Ridgeway successfully do this in Darwin's Soldiers: Schrodinger's Prisoners. It's also subverted in the third RP when Hans suggests this as a way to get into Pelvanida and James points out how that wouldn't work.
- Buck Rogers XXV (in the 25th Century) adventure XXVCA3 Deimos Mandate. When the pirates attack the RAM meeting, Mortimer tells the PCs to enter two air vent ducts and move around using them in order to ambush the pirates.
- Dune: Chronicles of the Imperium main rules, adventure "Instrument of Kanly". The agents of House D'murjzin enter and exit the 35th floor of the Adici Enterprises corporate headquarters through an air vent.
- Dungeons & Dragons, Dungeon magazine adventure "Granite Mountain Prison". One way for the Player Characters to enter the title jail is to climb down the main ventilation shaft and pass through the air ducts in the facility until they can get to the cell of the prisoner they're trying to break out.
- Chaosium's ElfQuest RPG main rules, adventure "The Dying River". The elf PCs can get inside the troll tunnels by finding one of the airholes that the trolls use as a ventilation system.
- Encounter Critical supplement Asteroid 1618. Small creatures can pass through The Vanishing Pyramid's ventilation system, but they must roll well or either get lost and exit in the wrong room or have to fight off packs of Raider Rats. If they survive they can scout out the contents of 2-8 rooms before having to roll again.
- Necromunda has this as a territory which gives the option of starting behind your opponent. Jutified as Imperial hive cities can have ventilation shafts kilometers wide.
- Paranoia 1E supplement Acute Paranoia, adventure "Outland-ISH". When the Troubleshooters are trying to get to ISH sector their High Programmer opponent tries to stop them by putting a convoy of vehicles across their path. They can get around this by finding and using an air vent passage.
- Shadowrun supplement State of the Art 2063. HVAC (Heating, Ventilation and Air Conditioning) systems have ductwork that can be used by shadowrunners to infiltrate corporate buildings. Knight Errant Security recommends that the ducts be made too small to allow entry by intruders.
- FASA's Classic supplement Action Aboard: Adventures on the King Richard. A paragraph details how the air ducts can be used to move around the ship.
- Challenge magazine #32 adventure "A World On Its Own''. One way for the PCs to get into the starport is to go through the service ducts for air circulation and electronics lines. The only problems are that most of the ducts are barely large enough for human beings and the chance of getting lost.
- Apollo Justice: Ace Attorney:
- The only reason the title character's client in the third case is accused of the murder is that it's a Locked Room Mystery and he's the only one small enough to fit through the vents (where they found his fingerprints). He did escape the crime scene through the vents, but didn't commit the murder.
- Also, the air vents were used by Lamiroir to get from one side the stage to the other quickly for her part in the magic act in the middle of her song. They are stated to be large enough for her to walk, albeit hunched over and there was staff waiting at either end to help her.
- Phoenix Wright: Ace Attorney Dual Destinies gives us a variant - Apollo suggests that someone walked through an air vent, but investigating the thing later shows that while it was possible, it was certainly not done and he has to come up with another defense.
- The Hard Times: "Evil Villain Ensures Lair's Air Vents Extra Wide", large enough to accommodate one adult man or a pair of sexy lady ninjas. The same villain also installs a Laser Hallway.
- Played straight in Magical Girl Hunters when sneaking into the Mashihaishi Ultra building. The confusing layout is lampshaded with Yoi asking directions of other people traveling through the same vent system.
- SCP Foundation
- SCP-932 ("Night Feeder"). During the containment breach described in Incident Report 932-02 SCP-932-06 escaped, apparently by somehow getting into Site-09's air ducts. While in the air ducts it reproduced, creating SCP-932-07 and SCP-932-08.
- SCP-1341 ("JUNGLE IN A JAR"). Doctor Boyd, the lead researcher on SCP-1341, wrote an account on the outbreak that led to the site being overrun with jungle plants. The last entry is his statement that he's going to commit suicide.
- SCP-2978 ("Motherburg"). The SCP-2978-B entities being held in Site 17 change a wireless modem into a flying vehicle and start to explore. Three minutes later the vehicle enters a ventilation duct and visual contact with the vehicle is lost.
- Tech Infantry has a sequence where a space station is captured by rebels, and they lock Xinjao O'Reilly, the chief engineer on one of the space docks, in a tool storage closet with his engineering crew. They hang a lampshade on what a stupid move this is, grab a bunch of tools, and escape into the maintenance passageways between bulkheads. They make life very difficult for the rebels controlling the station for a while.
- Kai tries to use one of these in the first episode of the Chronicles of Syntax to get out of the school. It doesn't quite work out how he expected.
Kai: Okay, this thing is definitely getting smaller. I might just hyperventilate myself into a coma down here. They'll find me years later, turning to dust in the fetal position. Can I even get into the fetal position? I don't care. Just keep moving. Just keep moving forward...
- Duct Hunt, a parody of the Metal Gear series made by Rocket Jump, deconstructs almost every aspect of this trope, including the way some players tend to use it in Metal Gear.
- Mercs has this done by Varisa and Creed to sneak around the ship during the "Hijack" episode. At one point, one of the mooks tracks Varisa by the banging noises in the ductwork and ambushes her when she comes out.
- To this day, criminals will attempt this trope at any number of buildings where they can find a suitable opening. The difficulty they will encounter is that ducts don't stay the same size or shape all that often. The added difficulty of straight up-and-down ducts will see many criminals slipping and falling to become wedged or even killed by the fall. Even worse for some criminals is they may attempt this on holidays or weekends to avoid being heard clambering through the ventilation. When they become trapped, they must wait days without food or water in extremely uncomfortable positions for somebody to discover them. Given that some buildings are closed for months at a time (if not permanently), it's not surprising that several unlucky burglars have ended up dying of thirst or exposure before being found when people finally return and notice a smell, or sometimes aren't discovered at all until the building undergoes maintenance or is demolished.
- This rather dim female convenience store thief in Edmonton attempted this trope. While the RCMP was busy wrestling her boyfriend and partner in crime, she found an opportunity to sneak into the back room and then clamber into an air vent exhausting air from the space above the ceiling. While she managed to pick a vent large enough to fit through, she forgot the fact that tiled ceilings aren't designed to take any weight, and took quite a brutal fall (headfirst!) onto a metal shelving unit underneath. With this obviously catching the attention of the officers who had just finished subduing her accomplice, the woman wisely gave herself up.
- In Real Life, small animals tend to be more successful at this trope than humans (they're small enough to get inside easily, they're light enough that the ducts can support their weight and they don't make as thunderous a noise while they move around). Depending on the animal, they can still be very loud as claws or nails make a racket running on metal.
- During and around The Dung Ages, a popular way to infiltrate a stronghold was to climb through the privy chute. This had varying outcomes; either they made it, and incidentally killed Edmund II by puncturing his arse, or they got stuck and died in there, or they suffocated and then died in there. After such sieges, those chutes had to be cleaned elaborately and swept through because of all the stuck-up cadavers.
- This is how the castle of Chateau Gaillard was defeated when the new owner of the castle, John, (yes that Prince John brother of Richard the Lionhearted) added a new latrine to the fortress near the front giving the once impregnable castle a massive new entrance to be exploited (the new chute was 2 meters square at the base and was outside the castle's moat). The original castle only having small chutes positioned where entering them would be foolhardy. All because John was too lazy to use the latrine at the middle or back of the castle.
- According to some sources, this was how Finnish Cudgel War leader Jaakko Ilkka escaped from his imprisonment in the Turku Castle.
- This was attempted in 1994 by Cleveland Indians pitcher Jason Grimsley to try to switch out teammate Albert Belle's corked bat before the umpire could find out he was cheating. Going through 10 feet of ducts and a false ceiling, he might have even gotten away with it if he hadn't replaced it with an autographed bat.
- Defied in Sensitive Compartmented Information Facilities, a.k.a. SCIFs, where top-secret intelligence information is handled in the United States have a list of regulations on construction of air vents, including grates to prevent entry and deliberate metal disconnects to avoid sound transfer.
- Successfully done by serial killer Ted Bundy. While in prison awaiting trial on one of many murders he was suspected in, he climbed through the roof of his cell (he had dieted and lost enough weight to make this possible), crawled across the floorboards into the adjoining warden's apartment (the warden and his wife were out at a New Year's Eve party), and simply walked out of the apartment into freedom. He was caught several weeks later, but not before adding several more victims to his list.
- When Kingsley Ofosu and 8 other Ghanians stowed away on a Europe-bound cargo ship, he escaped from the ship's murderous crew (the other stowaways were not so lucky), by shimmying up one of these.
- Quawntay Adams managed to escape from a jail by going into the subceiling and out through a vent. It was harder than it sounds; after getting a hacksaw blade to get through the ceiling, he had to both time the guards, evade the cameras-including the one in his cell-and get to his accomplice outside. His grand total of freedom? Seven hours.
- On a G4 special one of the famed Bioware doctors mentioned how as a child his teacher locked him in the closet for misbehaving, he climbed from the closet into the drop ceiling Breakfast Club style. After crawling back into his classroom he positioned himself over where the teacher was standing and dropped a lugie on them.
- Attempted unsuccessfully by Jamie Minor. She tried sneaking into her workplace by the air ducts but got trapped, and was found dead over a month later.
- Russian President Boris Yeltsin was thought to have done this once during a stay in Washington D.C. in order to evade security (the security aimed at protecting him) so that he could go out for a night on the town unburdened by bodyguards. In reality the president only unscrewed the vent as a decoy and or prank then used an unlocked window to "escape".
- Inverted — if only just — in real life basements containing an "egress window". This is intended to assist folks in their escape in the event of a house fire or emergency, but many folks often leave it open to get some air circulation going. Furthermore, many people are too large to make proper use of them.
- Freddy Swanson, an inmate in Monterey County, California, successfully pulled off this trope in December of 2014.
- In 1992, convicted murderer Richard Lee McNair and two other inmates escaped from North Dakota State Penitentiary by crawling through an air vent in an education room and making their way to the roof of the building. After crossing several more rooftops, they dropped 15 feet to the ground outside the main wall and escaped. The other two inmates were apprehended within hours, but McNair remained free for 10 months before being re-arrested.
- Attempted by a pair of students in the US to steal an exam paper in the middle of the night. The air duct bit worked, but the tutor was working late.
- A number of people have discovered to their dismay that air ducts and suspended ceiling grids are intended to support air and suspended ceiling tiles respectively, both of which are much lighter than human beings. Whether this discovery led to injury/death, imprisonment, or just embarrassment depends on where they fell through at.
- Theatres not infrequently have "hidden passages" installed over the "house" (audience seating area) for maintenance and adjustment of lighting or sound equipment that would be difficult or awkward to reach in any other way. However, these generally don't "go" anywhere and you usually have to exit back out the same way you came in (A really enterprising person might rappel down from a catwalk, but anyone doing so would almost certainly be in full view of the audience and draw more attention than they would have had they just walked in the main door quietly.)