HVAC
Air curtain and door heater field guide for commercial HVAC
Match the unit to the door width, mount it tight to the header, aim it slightly outward, wire the door switch, and prove the stream reaches the floor.
Direct answer
An air curtain is a unit mounted over a doorway that blows a controlled high-velocity stream of air down across the opening, forming an invisible barrier that separates inside from outside while the door is open. It holds conditioned air in and keeps infiltration, insects, dust, and fumes out. The stream has to reach the floor to work.
Key takeaways
- An air curtain blows a high-velocity air stream down across an open doorway, forming a barrier that holds conditioned air in and keeps infiltration, insects, dust, and fumes out.
- An air curtain only works if the stream reaches the floor with usable velocity; the bottom of the opening, farthest from the unit, is always the weak point.
- Pick a unit whose rated throw exceeds door height by 10 to 20 percent, span the full door width with no gap, and confirm against manufacturer data.
- Wire the curtain to a door switch so it runs only when the door is open; running behind a closed door wastes energy and pulls air the wrong way.
- AMCA 220 certification lets a curtain replace a code-required vestibule under ASHRAE 90.1-2019 and IECC, needing about 6.6 ft/s (400 ft/min) near the sill, aimed 20 degrees outward.
What is an air curtain?
An air curtain, also called an air door, is a unit mounted over a doorway that blows a controlled, high-velocity stream of air down across the opening. That moving sheet of air forms an invisible barrier between inside and outside. While the door stands open, the barrier holds the conditioned air in and keeps the outside air, along with the insects, dust, and fumes it carries, from pouring through the gap.
The whole device is simple. A fan pulls room air into an intake, an internal housing speeds it up, and a long narrow nozzle directs it straight down the face of the opening. The air strikes the floor, splits, and most of it rolls back toward the intake to be used again. That recirculation is what lets a curtain run on a fraction of the air a door-sized opening would otherwise leak.
It does not seal the door. Nothing about a moving air stream is a gasket. What it does is cut the free exchange of air through an open door from a flood to a trickle, which is enough to hold a temperature difference, a pressure relationship, or an insect line that an open door would erase. The barrier only exists while the unit is running and only works if the stream actually makes it to the floor.
Why a building puts a unit over the door
Three problems push an owner toward an air curtain, and they rarely show up alone. The first is energy. An open door at a busy retail entry or a loading dock dumps conditioned air outside and drags unconditioned air in, and the heating or cooling plant chases that loss all day. Cut the exchange and the plant stops fighting the door.
The second is comfort. Stand near an open entrance in January and you feel the cold draft rolling across the floor. A heated curtain tempers the stream so the air falling across the entry is warm instead of raw, and the cold sheet that used to spill into the lobby stops at the door. Customers and staff working the front feel the difference even when they do not know why.
The third is exclusion, and this is the one that turns a nicety into a requirement. Flies and other insects cannot push through a strong air stream, which is why food service leans on curtains at back doors and dock doors that have to stay open. Dust and exhaust fumes get held out of clean spaces the same way. The pressure side of this, holding a space slightly negative or positive to its neighbor, is the same balance the building's exhaust and makeup air sets, and the commercial exhaust ventilation guide works through that relationship in detail. An air curtain helps hold a pressure line at an opening that would otherwise blow it apart.
How does an air curtain work?
An air curtain works by turning fan energy into a coherent jet of air aimed across the opening. The fan, usually a line of cross-flow or centrifugal blowers, draws room air in through a filtered or louvered intake. The housing accelerates that air and feeds it to a discharge nozzle that runs the full length of the unit. The nozzle shapes the air into a flat, fast, fairly straight stream and sends it down the door face.
The stream stays organized for a distance, then it strikes the floor and breaks. Most of it, on the order of 80 percent, deflects back toward the inside and rises to the intake to be drawn through again. The rest spills to the outside. That split is the mechanism. Because the bulk of the air recirculates inside the building, the curtain separates the two environments without continuously pumping conditioned air out the door.
The single thing that makes or breaks the whole arrangement is whether the stream reaches the floor with enough speed left to deflect instead of dissipate. A jet that runs out of energy halfway down leaves the bottom of the doorway wide open, which is exactly where infiltration and crawling insects come through. Velocity at the nozzle is easy. Velocity at the floor is the number that counts, and it is the one people forget to check.
The stream has to reach the floor
Say it plainly: a curtain that does not reach the floor with usable velocity is not doing its job, no matter how much air it moves at the nozzle. The barrier is only as good as its weakest point, and the weak point is always the bottom, farthest from the unit, where the jet has spread and slowed.
Two things set whether the stream gets there. One is the velocity and air volume the unit produces. The other is the mounting height, because the higher the nozzle sits above the floor, the more distance the jet has to hold together before it lands. Manufacturers rate each unit for a maximum mounting height, and that rating is the throw the unit can actually deliver, not a hopeful number. A common rule of thumb is to pick a unit whose rated throw exceeds the door height by 10 to 20 percent so there is margin at the sill, but confirm the figure against the manufacturer's data for the specific model.
This is where a tall door punishes a unit chosen by door width alone. A cross-flow unit that performs beautifully over a 7 ft storefront can fall apart over a 12 ft door, because the jet simply cannot carry that far. For the tall opening you move to a centrifugal or industrial unit built for the height. Pick on width and you may cover the opening side to side while leaving the bottom third uncontrolled. The fix is to verify reach, by the rating before install and by feeling the stream at the floor after.
Unheated versus heated air curtains
The first fork in selection is whether the unit heats the air or only moves it. An unheated, or ambient, air curtain provides separation alone. It blows room-temperature air across the opening to hold the barrier, and that is all it does. For insect control, dust exclusion, and holding a cooled space, separation is often all you need, and an ambient unit is the simpler, cheaper machine.
A heated air curtain adds a coil or element so the stream comes off the nozzle tempered. That buys two things: it kills the cold draft at the entry for comfort, and it keeps the falling air from chilling the floor and the people near the door in winter. The heat is a comfort and condensation tool, not a substitute for the separation, so a heated unit still has to be sized and aimed to reach the floor like any other.
Heated units split by how they make the heat, and the choice usually follows whatever the building already has. Electric is the simplest to install because it needs only power, but it draws real current and the feeder has to carry it. Hot-water and steam coils tap the building's existing heating plant, which is efficient where that loop already runs past the door. Indirect gas-fired units show up on big warehouse and industrial doors where gas or propane is the cheap heat. Match the heat source to the building, then size the curtain for separation first and heat second.
| Type | How it heats | Where it fits |
|---|---|---|
| Unheated (ambient) | No heat, separation only | Insect and dust control, cold-space holding, mild climates |
| Electric | Resistance elements, needs power only | Retail entries, smaller doors, no heating loop nearby |
| Hot water or steam | Coil fed from the building heating loop | Buildings with a loop already at the door |
| Indirect gas-fired | Gas or propane burner, separated combustion | Large warehouse, dock, and industrial doors |
Horizontal overhead versus vertical side mount
Most curtains mount horizontally, hung tight to the header above the door with the nozzle blowing straight down. Overhead mounting is the default because the air works with gravity and a single unit covers the opening. For the ordinary storefront, restaurant door, or dock door, horizontal overhead is what you spec and what you will see installed almost everywhere.
Vertical side mounting puts the unit alongside the opening, blowing horizontally across it. You reach for vertical when the door is too tall for an overhead unit to throw down, too wide to cover from the top, or when there is no header room to hang a unit. Drive-through windows, very high warehouse doors, and some hangar and equipment openings get side-mounted units, sometimes one on each jamb blowing toward the middle.
Vertical units fight gravity, so they need more velocity to hold a coherent stream across the gap, and a wide opening may need a pair. The orientation does not change the rule that matters: the stream still has to cross the full opening with usable velocity at the far side, top to bottom or jamb to jamb. Mount it where it can do that, not where it is easiest to hang.
Where air curtains earn their keep
Air curtains land in a handful of spots, and the reason differs at each. At a retail or commercial entry the job is energy and comfort: hold the conditioned air, kill the draft, and keep the front of the store sellable in the worst weather. The door has to stay welcoming and open, so the curtain does the closing.
Restaurant and commercial kitchen doors are mostly about flies and the health code, covered in its own section below. Loading docks and warehouses run their doors open for hours, so the curtain there fights a constant, large air exchange and often a temperature swing on top of it. Cold storage and freezers use a curtain to hold the cold and stop the frost and condensation a warm-air intrusion creates. Drive-throughs use side-mounted units at the service window.
The pattern across all of them is an opening that has to stay open while still separating two environments. Pick the type by what the opening is fighting. An insect line wants velocity and full coverage. A winter entry wants heat plus reach. A freezer wants velocity tuned to resist warm, humid air rolling in at the sill. The deeper applications get their own sections next.
| Application | Main job | Note |
|---|---|---|
| Retail or commercial entry | Energy and comfort | Heated unit in cold climates to kill the entry draft |
| Restaurant and kitchen | Fly and insect exclusion | Food-establishment certification often expected |
| Loading dock and warehouse | Large air-exchange control | Doors open for hours, often big temperature swing |
| Cold storage and freezer | Hold cold, stop frost and condensation | Velocity at the sill resists warm, humid infiltration |
| Drive-through window | Comfort and insect control | Usually vertical side mount at the window |
Fly and insect control in food service
A strong, full-width air stream is one of the few things that reliably keeps flying insects out of a doorway that has to stay open. Insects cannot make headway against the jet, so the open back door or dock door stops being an invitation. This is why food service is the largest single use for air curtains, and why the unit is often there to satisfy a code, not just to make the kitchen pleasant.
The FDA Food Code recognizes air curtains, also called air doors, among the acceptable means of controlling insects when an outer opening is kept open for ventilation or operations. Local jurisdictions adopt and amend the Food Code on their own schedule, so the exact provision and how an inspector applies it vary, and you confirm the adopted edition with the authority having jurisdiction. NSF/ANSI 37 is the certification standard written specifically for air curtains used at entranceways in food and food service establishments, and a health inspector who wants a certified unit usually wants that listing.
The detail that fails inspections is coverage and velocity at the floor. A curtain narrower than the door, or one mounted so high the stream is spent before it lands, leaves a gap at the bottom that flies walk right under. For insect control the stream has to span the full opening and still be moving at the sill, which is where the bugs actually cross. A unit that looks like it is running and a unit that is actually holding the line are two different things, and only the floor reading tells them apart.
Cold storage and freezer doors
On a cooler or freezer door, the curtain holds the cold in and, just as important, holds warm humid air out. Every time warm air rolls into a freezer it carries moisture that turns to frost on the coils, the product, and the floor, and to fog and condensation in the doorway. That frost drives up defrost cycles and energy use, and the wet floor at a freezer threshold becomes a slip hazard and an ice problem fast.
The cold-room case is harder than a comfort entry because the temperature difference is large and the cold, dense air inside wants to spill out across the sill while warm air pushes in above it. A unit picked for a storefront will not hold a freezer line. You want a unit rated for cold-storage service and enough velocity at the sill to resist the warm, humid intrusion, with one source citing roughly 2.5 m/s at the sill as a working target. Treat any such figure as a starting point and confirm the selection against the manufacturer's cold-storage data for the actual temperature difference.
Curtains on freezers are usually a supplement, not the only barrier. They pair with strip curtains or fast-acting doors and earn their place by cutting the frost and fog during the seconds the door is actually open and traffic is moving through. Run the unit only while the door is open, or it will pull a steady stream of warm room air into the cold space and work against itself.
Loading docks, drive-throughs, and facility entries
Loading docks are the hardest duty a curtain sees. The door is large, it stays open while the trailer is worked, and the opening faces weather and traffic. These get the high-output centrifugal or industrial units, often indirect gas-fired in a cold climate, and they have to be sized for both the width and the full height of an overhead door. Undersize a dock unit and it is decoration.
Drive-throughs are the opposite scale. The service window is small but it cycles constantly, and the staff lives right in the draft. Vertical side-mounted units at the window hold comfort for the worker and keep insects out of the food-handling zone without blasting the customer. Aim and velocity matter more than raw size at a window.
Facility and equipment entries, including data centers and clean industrial spaces, use curtains to hold a pressure relationship and keep dust and outside air out of a controlled environment at man doors and equipment openings that have to stay usable. The thermal management those spaces depend on, and how the room's design pressure and ventilation fit together, is the territory of the HVAC system types overview and the building's exhaust and makeup-air design. The curtain is one piece of holding that boundary at the opening, not the whole strategy.
How do you size an air curtain?
Sizing starts with two measurements: the door width and the door height. The unit, or a continuous line of units, has to span the full width with no gap, because any uncovered section of the opening leaks as if there were no curtain at all. A 10 ft door needs 10 ft of nozzle, whether that is one long unit or several butted together with the discharge kept continuous.
Height drives the harder half of the selection. The unit has to throw far enough that the stream still has usable velocity at the floor, so the rated mounting height has to meet or beat the actual door height. Then you match the air volume and velocity to the environment: a comfort entry asks less of the stream than a freezer door or a windy dock facing a large temperature difference. Manufacturers publish the velocity, air volume in CFM, and maximum mounting height per model, and an AMCA-certified rating is the trustworthy version of those numbers. Size to the manufacturer's data and the AMCA rating, not to a catalog photo.
The two errors that show up most are picking on width while ignoring height, which leaves the bottom of a tall door uncontrolled, and picking a unit one notch too small for the duty so it covers the opening but cannot hold the line against real wind or a real temperature difference. When the application is demanding, size up. The cost difference between adjacent models is small next to the cost of a curtain that does not actually separate the two environments.
Controls: the door switch, the thermostat, two speeds
The control that matters most is the door switch. The curtain should run only when the door is open, and it knows the door is open from a microswitch, a magnetic contact, or a signal off the automatic door operator. Open the door, the unit comes on. Close it, the unit shuts off or drops to a setback. A curtain wired to run continuously, or one with the door switch never installed, wastes energy and, on a cold-storage or pressurized space, actively works against the building by moving room air the wrong way while the door is shut.
Heated units add a thermostat so the heat modulates or cycles to a setpoint while the separation keeps running, plus high-limit and freeze protection on water and steam coils per the manufacturer. Many units also offer two-speed or variable fan control, which lets you run a lower, quieter, lower-energy speed in mild conditions and the full output when the weather or the traffic demands it.
Wire the interlock the way the manufacturer specifies, and prove it on commissioning. Open the door and confirm the unit starts; close it and confirm it stops or steps back. It is a five-minute check that catches the most common operating waste there is, a curtain running flat out behind a closed door because nobody verified the switch.
AMCA 220 and certified performance
AMCA 220 is the test standard for air curtains, titled Laboratory Methods of Testing Air Curtain Units for Aerodynamic Performance Rating. It defines how a unit's velocity, air volume, throw, and uniformity get measured so the numbers from one manufacturer mean the same thing as the numbers from another. A unit certified to AMCA 220 has had those ratings verified to a common method, which is the difference between a catalog claim and a number you can build a code submission on.
The reason this matters beyond comfort is that the energy-code path for using a curtain in place of a vestibule leans on the AMCA-certified rating. The criterion commonly cited for that substitution is a jet that still delivers a defined minimum velocity near the floor, on the order of 6.6 ft per second, about 400 ft per minute, measured close to the sill, aimed at least 20 degrees toward the opening. Treat those specific figures as the AMCA and code numbers to verify against the adopted edition and the certified rating, not as something to take from a guide.
When a job actually depends on the curtain's performance, an energy-code submission, a freezer line, a health inspection, specify a unit with a published AMCA-certified rating and keep that rating in the submittal. An uncertified unit may move plenty of air and still not have the documented floor velocity the code or the inspector wants to see.
Can an air curtain replace a vestibule?
Yes, in many cases an AMCA-certified air curtain can stand in for a code-required vestibule, but the path runs through the energy code and the certified rating, not the contractor's preference. ASHRAE 90.1, in its 2019 edition, added air curtains as an allowed alternative to vestibules at building entrances, and the IECC and the green-construction overlay code opened that door earlier. The result is that on many commercial buildings a properly certified and installed curtain satisfies the same intent as the vestibule the code would otherwise require.
The qualifier is real. The substitution generally requires a unit tested and certified to AMCA 220, delivering the specified floor velocity, installed per the manufacturer's instructions, and the allowance comes with conditions on building type and size in the standard. Reported studies put a certified curtain at parity with or better than a vestibule for energy on buildings above a few thousand square feet, which is the evidence the code change rested on. Whether it applies to a given project depends on the adopted code edition, local amendments, and the building's occupancy and area.
So the honest answer to the owner who wants to skip the vestibule and save the floor space is: often yes, if you use a certified unit and document it. Pull the adopted energy code, confirm the air-curtain exception and its conditions, specify a unit whose AMCA-certified rating meets the floor-velocity criterion, and keep the rating and the installation details in the record. Do that and the curtain is a defensible substitution. Skip the certification and it is a guess the inspector can reject.
Installing an air curtain
Mount the unit tight to the header, directly over the opening, with the discharge nozzle as close to the plane of the door as the structure allows. A gap between the unit and the wall above the door lets room air short-circuit into the intake and weakens the stream, and setting the unit back from the door face lets the jet wander off the opening. Tight and aligned is the whole game on placement.
Cover the full width. If one unit is not long enough, line up multiple units with the discharge kept continuous so there is no dead gap between them where the opening leaks. Confirm the structure and the mounting hardware actually carry the weight, because these units are heavier than they look, especially the gas and coil models, and they hang over a doorway people walk under.
Make the connections to suit the type. Electric units need a circuit sized for the heater load, which is not trivial on a large heated unit, so the feeder and breaker get sized to the nameplate. Water and steam units need supply, return, control valve, and a way to handle condensate or freeze risk. Gas-fired units need gas piping, combustion venting per the listing, and clearances. And run the door-switch wiring while the unit is open and accessible, because retrofitting the interlock later is the job everyone postpones and never finishes.
Aiming the nozzle slightly outward
Aim the stream slightly toward the outside, not straight down. The reason is the wind and pressure pushing in from outside: a stream angled a little into that pressure holds the line at the sill, while a stream aimed dead vertical gets bent inward by the incoming air and gives up the bottom of the opening. The common target is a modest outward tilt, with code-related vestibule work citing at least 20 degrees toward the opening, but the exact angle is set to the conditions and the manufacturer's guidance.
Most units have an adjustable nozzle or louver for exactly this. On commissioning, set the aim, then check it by feeling the stream at the floor across the full width of the door with the door open and any normal wind present. The goal is a stream that lands at or just outside the threshold and stays strong at the sill, not one that has fizzled to a breeze by the time it gets there.
Re-aim if the conditions change. A unit dialed in on a calm day can be wrong for a windy exposure, and a freezer or a pressurized space may want a different angle than a comfort entry. The aim is not set-and-forget. It is the cheapest adjustment that turns a marginal install into one that actually holds.
Maintenance
An air curtain is mostly a fan, so the upkeep is mostly about keeping the air moving cleanly. Pull and clean or replace the intake filter on the units that have one, and clear dust and grease off the intake and the blower wheels on the ones that do not. A loaded intake or a fouled wheel quietly drops the air volume, and a curtain that has lost a third of its output may still look like it is running while the stream no longer reaches the floor. Kitchen units load with grease faster than anyone expects.
On heated units, service the heat side too. Check electric elements and their contactors, the coil and valve on water and steam units, and the burner, venting, and safeties on gas-fired units per the manufacturer's schedule. The high-limit and freeze protection are there to keep a failure from becoming a fire or a burst coil, so they get tested, not assumed.
Check the bearings and listen for the fan going noisy or out of balance, and reconfirm the door switch still trips so the unit is not running behind a closed door. The performance loss on a curtain is usually gradual and silent, which is why a quick airflow-at-the-floor check belongs on the maintenance visit, not just an eyeball that the unit powers on.
Why isn't my air curtain working?
When a curtain is installed but the door still leaks, draft, or lets flies in, the cause is almost always one of a short list, and they are easy to check in order. Most start with a stream that never reaches the floor.
Undersized or mounted too high is the most common. The unit cannot throw the door height, so the bottom of the opening is uncontrolled and everything you were trying to stop comes through there. Next is no door switch, or a switch that failed, so the unit either runs behind a closed door wasting energy or does not come on when the door opens. Then there is coverage: a unit narrower than the door, or units left with a gap between them, leaks at the uncovered section. And there is aim: a nozzle pointed straight down, or even tilted inward, that gets folded back by the incoming air and abandons the sill.
Wrong type for the duty hides behind all of these. A comfort-entry unit hung on a freezer or a windy dock can be sized to the width, switched correctly, and aimed right and still fail, because it does not have the velocity to hold that temperature difference or that wind. And a neglected unit with a clogged filter or a greased-up wheel fails slowly as its output drops. Check reach at the floor first. The floor reading tells you which of these you have faster than any other test.
What to document
The record on an air curtain is what lets the next person confirm it was selected right and prove it to an inspector. The key items are the unit make and model with its AMCA-certified rating, the door width and height it serves, the type and heat source, how it is controlled, and the velocity actually measured at the floor on commissioning.
On a vestibule substitution or a health-code install, the rating and the floor reading are the whole case. Keep the AMCA certification, the manufacturer's installation data, the code provision relied on, and the measured floor velocity together, because that package is what answers the inspector and the question that surfaces a year later when someone asks why the building has no vestibule.
| Field to record | Why it matters |
|---|---|
| Make, model, AMCA rating | Ties performance to a verified, certified number |
| Door width and height | Confirms the unit spans the width and throws the height |
| Type and heat source | Drives the connections and the maintenance plan |
| Control method | Proves the door switch and setback are in place |
| Measured floor velocity | The reading that shows the stream actually reaches the floor |
| Code provision relied on | Backs a vestibule substitution or food-code install |
Common mistakes
- Undersized or mounted too high, so the stream loses velocity and never reaches the floor.
- No door switch, or a failed one, so the unit runs behind a closed door and wastes energy.
- Unit narrower than the door, or a gap left between paired units, leaking at the uncovered section.
- Nozzle aimed straight down or tilted inward instead of slightly outward toward the opening.
- Wrong type for the environment, such as a comfort-entry unit on a freezer or a windy dock.
- Neglected intake filter or fouled blower wheel quietly cutting the air volume over time.
- Specifying an uncertified unit where an AMCA-certified rating is needed for the code path.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
AMCA 220, Laboratory Methods of Testing Air Curtain Units for Aerodynamic Performance Rating, is the standard that governs how a unit's performance is measured, and an AMCA-certified rating is the credible source for velocity, air volume, throw, and mounting height. When a job depends on the curtain holding a line, that certified rating is what you specify against and keep in the record.
The manufacturer's published data controls the specific numbers for any model: the velocity, the CFM, the maximum mounting height and throw, and the connection and clearance requirements. Treat any general velocity or air-volume figure, including the floor-velocity targets for cold storage or a vestibule substitution, as a value to confirm against that data and the certified rating, not as a fixed rule.
The energy code is where the vestibule question lives. ASHRAE 90.1, in its 2019 edition, and the IECC allow an AMCA-certified air curtain as an alternative to a required vestibule under stated conditions, so verify the adopted code edition, local amendments, and the building type and area against the actual standard before relying on it. For food service, the FDA Food Code recognizes air curtains among acceptable insect-control measures, with the adopted edition and the authority having jurisdiction controlling, and NSF/ANSI 37 is the certification standard for air curtains at food-establishment entranceways. Across all of it, the field facts that decide whether the unit works are the same three: the stream reaches the floor, the door switch runs it only when the door is open, and the unit covers the full door width.
Units, terms, and conversions
Air curtain specs come in a mix of names and units, so the same idea reads differently across a cut sheet, a spec, and a code section. The terms below are the ones that matter on selection and commissioning.
An air curtain is also called an air door, and the two terms are interchangeable. Velocity is given in feet per minute (ft/min) or meters per second (m/s); roughly, 400 ft/min is about 2.0 m/s. Air volume is in cubic feet per minute (CFM) or cubic meters per hour. Throw, or projection, is the distance the stream stays coherent, and it is the figure that has to beat the door height. Mounting height is the height of the nozzle above the floor, which is what the throw has to cover.
- Air curtain / air door
- A unit over an opening that blows a high-velocity stream across it to separate inside from outside
- Velocity
- Speed of the air stream, at the nozzle and, more importantly, at the floor, in ft/min or m/s
- Throw / projection
- Distance the stream stays coherent; it must meet or beat the door height
- Mounting height
- Height of the discharge nozzle above the floor, the distance the throw has to cover
- Deflection
- The split where the stream hits the floor; most rolls back inside, the rest spills out
- AMCA 220
- The test standard for air curtain aerodynamic performance; a certified rating is the credible number
FAQ
What is an air curtain?
An air curtain, also called an air door, is a unit mounted over a doorway that blows a high-velocity stream of air down across the opening. That moving sheet of air forms a barrier separating inside from outside while the door is open, holding conditioned air in and keeping infiltration, insects, dust, and fumes out.
Do air curtains save energy?
Yes. By cutting the air exchange through an open door, an air curtain holds conditioned air inside and reduces the infiltration the heating or cooling plant has to fight. Reported infiltration reduction commonly runs around 60 to 80 percent. Actual savings depend on the door, the climate, the unit, and whether the stream truly reaches the floor.
Can an air curtain replace a vestibule?
Often yes. ASHRAE 90.1-2019 and the IECC allow an AMCA-certified air curtain as an alternative to a required vestibule under stated conditions. The unit must be tested to AMCA 220, meet the floor-velocity criterion, and be installed per the manufacturer. Verify the adopted code edition, local amendments, and building type before relying on it.
How do you size an air curtain?
Match the unit length to the full door width so there is no gap, then pick a unit whose rated mounting height and throw meet or beat the door height. Match the velocity and CFM to the environment, harder for freezers and docks. Size to the manufacturer's data and the AMCA-certified rating, not a catalog photo.
Heated or unheated air curtain: which do I need?
Use unheated, or ambient, when separation alone is the goal, such as insect control, dust exclusion, or holding a cooled space. Choose heated to kill the cold draft at an entry and prevent condensation in winter. Heat is a comfort tool, so a heated unit still has to be sized and aimed to reach the floor.
Do air curtains keep flies out?
A strong, full-width stream that reaches the floor keeps flying insects from pushing through an open door, which is why food service relies on them. The FDA Food Code recognizes air curtains among acceptable insect-control means, and NSF/ANSI 37 certifies units for food entranceways. The gap that lets flies in is usually a stream that does not reach the sill.
Why isn't my air curtain stopping the draft?
Most often the stream is not reaching the floor because the unit is undersized or mounted too high, so the bottom of the opening stays uncontrolled. Check coverage across the full width, confirm the nozzle is aimed slightly outward, and verify the door switch. Wrong unit type for a freezer or windy dock is the hidden cause.
Should an air curtain run all the time?
No. Wire it to a door switch so it runs only when the door is open and stops or drops to setback when closed. A unit running behind a closed door wastes energy and, on a cold-storage or pressurized space, pulls air the wrong way. Prove the switch on commissioning by opening and closing the door.
How do air curtains help on freezer and cold-storage doors?
They hold the cold in and keep warm, humid air out, which cuts the frost on coils and product and the condensation and ice at the threshold. Cold rooms need a unit rated for that service with enough velocity at the sill to resist the warm intrusion. Curtains usually supplement strip curtains or fast doors, not replace them.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.