Ductwork Expectations vs Reality from TV and Cinema.
Hollywood has a big secret. Hollywood is in the HVAC business, and business is booming.
We’re not talking about equipment sales or building designs; we’re talking about good old-fashioned film sets created for crawling in the ductwork. Crawling in ducts has become a critical storytelling trope used by Hollywood writers. Action thrillers use ductwork as a major piece of espionage, where characters use duct to hide or as a means of escape. When in doubt, if there is no possible way out of a sticky situation, just climb into the air ducts. Millions, if not billions of dollars have been made in Hollywood by the vast array of movies that have used crawling in air ducts to make their plots work. There is only one problem. The ductwork portrayed in movies is highly inaccurate and includes components that are totally unrealistic, impractical, dangerous, and downright stupid. It may not be surprising to you that Hollywood would embellish something like this, but people seem to believe that crawling in ducts is a realistic option. Just ask these guys:
Growing up with a father in the HVAC business, no family action movie night was complete without a few comments about how inaccurate the ductwork crawling scenes were. After I entered the world of HVAC myself, I finally get it, and now I care too.
1. You’re trapped in a room. You have no way out…but wait. You see the air vent.
You see the vent - Video Clip First, you must get the “vent” open. There are many types of “vents.” In the HVAC world we call them air terminals, or RGDs, an abbreviation for registers, grilles, and diffusers.
R - Registers are typically rectangular or square metal frames that attach to the ductwork and have adjustable fins or louvers that allow you to direct the flow of air. They are commonly found on walls, floors, or ceilings and can be opened or closed to adjust the amount of air flowing into a room. These are standard in many residential applications.
G - Grilles are like registers, but instead of adjustable fins, they have horizontal or vertical bars that create a pattern on the surface. Grilles are typically used for return and exhaust air applications, and their primary function is to protect the ductwork from debris and maintain an aesthetic appearance. They are used in all kinds of commercial buildings. These are usually the vents used to escape in movies, as they are often located lower to the floor, are typically larger in size and would be the easiest option to gain access inside ductwork.
D - Diffusers are designed to supply air to a room and disperse the airflow evenly across a room. They have a curved or angled face with a series of small slots or holes that direct the air in multiple directions, creating a uniform air distribution pattern and, as a result, a more comfortable environment. Diffusers are typically installed in ceilings often used in commercial or industrial applications where occupant comfort is a top priority.
2. Time to open the vent and crawl in.
Crawl on in - Video Clip
One of the first things to point out is that these vents (RGDs) are fastened to the wall or ceiling. Lay-in diffusers for example sit in ceiling grids and would be impossible to crawl into. The only grilles that make sense to open are return or exhaust grilles. If you don’t have tools, you better hope the grille in the room is hinged. Hinged grilles often have an area for a filter in the face of the grille for easy replacement of filters within the room. I hope you found a screwdriver.
Figure 1 Lay-in Supply Diffuser Figure 2 Filter Return Grille
3. You’re in the duct.
In the ducts - Video Clip
Size The most obvious inaccuracy of Hollywood ductwork is the size. Most ductwork is much smaller than you might think if your only basis is watching movies. Ductwork in areas around occupied rooms is often around a foot in diameter, plus or minus a few inches. Ductwork entering the air terminals will usually be less than a foot. This is because the size of the ductwork changes based on where the duct is and how much air is passing through it. Ducts must be sized proportional to the amount of air that needs to be moved through it and its size is determined from the air velocity and pressure.
For example, a room needing 150 cubic feet per minute (CFM) of air will have low pressure ductwork entering and leaving the room sized at about 600 feet per minute (FPM) that’s only an 8-inch round duct or an 8”x6” rectangular duct. Even a room that needs 2000 CFM of air to cool the room will only be roughly a 22”x14 duct sized at 0.08” w.c. entering the room, not to mention it likely splits in size into smaller ducts that serve multiple grilles or diffusers in the room. Only near mechanical rooms, shafts, roofs, etc. is where you will find ductwork big enough to crawl in. It would quickly become cramped, and that’s ignoring all the tight bends you would have to wiggle through. Let’s say we have 20,000 ft2 of floor area served by a single air handling unit at 50,000 CFM at 2500 FPM That’s a big 4’x5’ duct to start, but then it splits in half evenly to 3’x4’ before it splits again to four 2’x3’ ducts serving the four quarters of the floor area, and only gets smaller as you continue. Doesn’t sound so comfortable now does it.
And let’s not forget that air ducts have other components in them that would obstruct your path. HVAC duct systems use dampers, fans, and other terminal equipment to control airflow. Fixed dampers, for instance, balance the air to maintain different airflows to various rooms, while variable control damper devices such as VAVs and venturi valves modulate the airflow to each room. These devices typically have set sizes for inlets ranging from 4”Ø to 20”Ø in diameter.
Figure 4 Not too bad for TV, but that duct is a little clean. (Duffer, M., & Duffer, R. (2019, July 4). E Pluribus Unum. Stranger Things, Season 3, Episode 6. Netflix.) Dustin stuck clip
Figure 5 Not as tight but not the worst, but how is that lighter still lit with all that air moving in there? Its literally a wind tunnel! (McTiernan, J. (1988). Die Hard. Twentieth Century Fox.)
Another inaccuracy is the cleanliness of the ductwork. In movies, the inside of ductwork is often portrayed as a clean and shiny metal surface, free of any dirt or debris. However, ductwork will often become dirty and clogged over time, especially if it is not properly maintained. This can reduce the efficiency of the HVAC system and even lead to health problems for occupants of the building. We routinely request duct cleaning on our renovation projects to ensure good performance for our replacement equipment.
Figure 6 What real ductwork looks like. Look at some of those screws on the right. Ouch. (JCL Air, 2020, https://jlcair.com/air-duct-cleaning/)
Figure 7 Winston looking relaxed in this nice clean ductwork. (Meriwether, E. (2012, October 23). Models. New Girl, Season 2, Episode 5. 20th Century Fox Home Entertainment.)
The noise level of ductwork is also often inaccurately portrayed in movies. In movies, ductwork is often portrayed as a silent system, allowing characters to communicate in whispers while hiding inside the ducts. Air in the ductwork can cause quite a bit of noise. The noise will fluctuate in volume based on static pressure and velocity of the air moving through the ductwork. In situations where the duct is near to the source of the air moving equipment, you would have noise issues with fan sound. Engineers need to consider the noise during design and situations often require sound attenuation at various points of the air stream.
I would also like to note that people in the rooms would obviously hear people talking and moving around in the ductwork, especially in situations where the duct grille is open to the room directly, as it is shown in most movies. Characters in ducts are often able to listen in on conversations or even record them by placing a device inside the ductwork. This would be a terrible way to eavesdrop on conversations. The sound of the HVAC system is likely to drown out anything you are trying to hear. Just keep this in mind: ductwork is literally a wind tunnel.
Figure 8 J.B. using a walkie talkie. Note that his hair isn’t blowing in the wind. (Lynch, L. (2006). Tenacious D in the Pick of Destiny. Red Hour Films.)
Weight At this point you may be wondering about weight. Could it at least support a person? Good question. Probably not.
Ductwork is typically installed in the ceiling or exposed at the top of the room, and is supported by hangers, rods, or other supports that are attached to the building's structural elements. The hangers are designed to support the weight of the ductwork and insulation only. They are not designed to hold weight beyond this.
Figure 9: Paul Blart falling after hiding in a duct. (Car,S., Carr, Wachtel,W., Smalley, S.S., Dilbeck, M., (2009) PAUL BLART: MALL COP. USA.)
Construction Besides the fact the duct hanging methods probably could not support your weight, crawling through ductwork is unsafe for several other reasons, including the screws used to hold the ducts together. Ductwork screws are typically designed to hold the ducts together and prevent air leakage, but they are not designed to support the weight of a person. Attempting to crawl through ductwork can cause the screws to loosen or break, which can cause the ductwork to collapse or detach from its supports. These screws would also likely cause a serious cut or snag any clothing and you wouldn’t have much room to avoid them even if the duct is big enough to fit a person.
Temperature Have you ever thought of why these characters look so cozy? Some of the temperatures in these ducts would not be pleasant. Ducts typically run air at around 55F for cooling and can get up to around 90F in heating. Not especially comfortable, especially with wind chill.
One of my biggest pet peeves is what HVAC-related props are used in these scenes. My favorite prop is its name’s sake, the propeller fan (prop fan) which is typically located in the ductwork, with the blades moving so slow you can see the outline of each blade. Prop fans are never used in these applications and are typically used in walls or roofs of rooms such as electric and mechanical rooms to move hot air out of the room. In the movies these fans are conveniently located in-line of huge ductwork with minimal blades and are accompanied by a disconnect or junction box within the ductwork. This would never happen as the fans could never build the static pressure needed to move that amount of air. Also, how are you going to get access to that junction box again after install? Just hop in the duct!
I'm a Nerd - Video Clip
Figure 10: Dustin going at the junction box. Huge duct, talking, clean, and a prop fan. Hits all the boxes. Then he rips out the wires without getting electrocuted. (Stanger Things Season 3 Episode 6 - 2019)
Figure 11: Prop Fans and running wires inside duct? What the heck is a light doing inside the ductwork? (Håfström, M. (2013). Escape Plan. Summit Entertainment.)
In conclusion, the portrayal of ductwork in movies is often highly inaccurate. From its size to its cleanliness, the movies often get it all wrong. While ductwork may make for a great plot device, it is important to remember that it is not designed for the purposes often portrayed in movies. If you want to learn more about the real-life functions and limitations of ductwork, it is best to consult with a qualified HVAC professional. If anyone reading this is in Hollywood, give us a call and F&T can set you straight.
For some encouragement, not all movies are completely unrealistic…
Figure 12: Lasseter,J. (1995). Toy Story. Buena Vista Pictures.
Here is a short list of some popular movies and TV shows featuring ductwork:
Die Hard, Die Hard 2
Paul Blart Mall Cop
Lethal Weapon 2
Enemy of the State
The Walking Dead
Ocean's 11, Oceans 12
The Italian Job
The Bourne Identity
The Silence of the Lambs
It’s Always Sunny in Philadelphia
Mr. and Mrs. Smith
Men in Black II
The Boondock Saints
Toy Story 2
Lilo & Stitch
Batman Arkham Series
Mechanical Design Engineer