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Evaporator Coil Issues
Expansion Valve Problems
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Water Leaks
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Airflow Problems
Restaurant HVAC starts with the air balance
Restaurant HVAC is an air balance problem before it is a comfort problem. The hood over your cook line moves a large volume of air out of the building every hour you trade, and what replaces it decides how the dining room feels, whether the hood captures, and how hard the front door is to pull. We design, install and service the whole air side for restaurants, bars and hospitality businesses across Suffolk and Nassau County.
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Almost every complaint in a restaurant starts at the hood
The exhaust fan serving your canopy runs continuously while the line is lit. Whatever it takes out of the building has to be replaced from somewhere, and the only question is whether you chose where it comes from or the building chose for you.
The system built to replace that air is called make-up air. In most restaurants it is a unit on the roof with its own fan, filter section and damper, sometimes with a burner in the airstream, discharging into a plenum at the front edge of the hood. It exists to hand the hood the air it needs so the hood does not have to take that air from your dining room.
When make-up air falls short of the exhaust, the building goes negative. It does not stop needing air. It takes the difference through the front door, the back door, the gap under the dish room door, the seams around a rooftop curb, the dryer vent, and the toilet exhaust duct running backwards. None of that air passes a filter or a coil on the way in, and all of it lands in a room you are paying to condition.
Push it the other way and the failures invert. Too much make-up air, or an exhaust fan that has slowed, and the building goes positive instead, with a different set of symptoms and the same loss of capture.
One item on that list should never be lived with. Where a building still runs a naturally vented gas water heater or boiler, a strongly negative kitchen can pull that flue backwards, which is reason enough to have a balance measured rather than adjusted by feel.
Balanced does not mean equal, and that is the part almost nobody explains. The kitchen is meant to sit slightly negative against the dining room, so air travels from the tables toward the line and out through the hood rather than the other way, while the building as a whole sits close to neutral against outside so no door is fighting a pressure difference. Holding both at once is the design, and the figures behind it come off the survey and the hood manufacturer's data for the canopy you have. The equipment side of the same building sits under commercial HVAC.
What the dining room has to be given
- Air it did not pull in itselfSupply through equipment, not infiltration at the threshold.
- Run time long enough for moistureTemperature and humidity, not temperature alone.
- A still roomNo throw across seated guests, no draft at the door.
- Lower pressure than the kitchenSo odor travels toward the hood and not the tables.
What the kitchen has to be given
- Air at the canopy faceA hood cannot capture what it cannot pull.
- That air at a workable temperatureOr somebody switches the supply off and the balance goes.
- Somewhere for its own heat to goEquipment, refrigeration and people all reject into one aisle.
- An exhaust fan doing what it did newRotation, belt and balance. Noise is not proof of volume.
See what the building does as the balance moves
The hood's exhaust volume is set by the canopy and the equipment under it. Make-up air is the side that gets sized, controlled, and switched off. Move the control and the panel names the symptoms in the words operators actually use.
Scroll the diagram sideways for the dining room end. Schematic, not to scale, and not a measurement of your building. Real figures come from a survey of your hood, your fan and your roof.
Exhaust well ahead of the make-up air
The front door takes a real pull to open and bangs shut behind people. Smoke and steam roll out from under the front edge of the canopy instead of going up it, and by mid service there is a haze that reaches the pass. The dining room is drafty near the entrance all winter and clammy all summer, and cooking smells reach the tables. A canopy needs air at its face to carry the plume up, and a starved kitchen has none to give, so capture falls off with the fan turning perfectly.
Add air, do not add fan. Confirm the make-up air unit is running, that its damper opens when the hood switch is on, and that its filters are not blinded.
A little short on make-up air
The door pulls harder than it should. The canopy holds the plume in the middle and loses it at the ends, usually worse the moment somebody opens the door to the dining room. There is a draft at the entrance that the first two tables feel and nobody else does. A shortfall this size still lets the kitchen work, so it gets lived with for years and shows up on the utility bill rather than in a complaint.
Both sides get measured before anything is changed. A make-up air unit that is running is not the same as one delivering what it was sized for, and a blinded filter, a damper that only part opens or a slipping belt will each leave it short.
Matched, which is the state worth defending
The door opens with normal effort. The canopy holds the plume across its whole length, including at the ends. The dining room sits where the thermostat says without a draft at the entrance, and the kitchen smell stays in the kitchen because the kitchen is held a little below the dining room, not level with it.
Filters on the make-up air unit, a damper that still travels, an exhaust fan belt in condition, and an interlock that has actually been tested rather than assumed.
Make-up air ahead of the exhaust
Cooking smells drift out to the dining room, because the kitchen is now pushing air toward the tables and the odor path has reversed. Doors want to swing open on their own. The hood looks like it is working and still loses the plume at the front edge, which happens when the supply discharges too fast or aims across the canopy face instead of down in front of it.
Confirm the exhaust fan is turning at speed before anyone touches the supply. After that it is a discharge and volume question at the plenum, set against the hood manufacturer's data for that canopy.
Make-up air well ahead of the exhaust
Doors blow open and are hard to close, and conditioned air leaves through every gap you paid to seal. In winter the pass is cold while the cooks are still hot at the range. In summer the whole building feels damp and the dining room air conditioning runs and runs without drying the room out, because a coil sized for a dining room cannot dry a river of humid air arriving from the next room.
Check the exhaust fan first, then the supply. A dead or slowed exhaust fan produces this exact picture, and it is the cheaper of the two answers.
One roof, two climates, and why a single thermostat cannot serve both
A restaurant asks one building to hold two conditions with almost nothing in common: people sitting still out front who notice a small drift and a draft on the neck, and a wall of cooking equipment out back with staff working hard beside it. A thermostat only reports the temperature where it hangs. Hang it in the dining room and the kitchen is on its own; hang it in the kitchen and the dining room gets cooled to keep the cooks comfortable.
What the guest is actually reacting to
Nobody says the dining room is at the wrong relative humidity. They say it feels stuffy, or they keep their coats on, or they order one drink and leave. Most of what a guest reacts to is air movement and moisture rather than the number on the wall.
The entrance does most of the damage. A vestibule, an air curtain, or a door that closes properly is worth more to the first two tables than another ton of cooling, and a door held ajar by building pressure defeats all three.
Moisture is the other half, and on Long Island the summer load is wet as much as it is hot. Equipment sized purely on temperature satisfies the thermostat quickly, shuts off, and never runs long enough to pull water out of the air. The room ends up cool and clammy at once, which shows as condensation on glassware and a smell that will not clear.
What gets looked at in a dining room
- Where the thermostat actually sitsOver a service station, in afternoon sun, or beside the door.
- The return air pathA room given supply with nowhere to return does not circulate.
- Diffuser throw over seated guestsAir landing on necks reads as a cold room even at setpoint.
- The entrance against building pressureClosers and weatherstrip are only as good as what they work against.
- Run time long enough to dehumidifyShort cycles satisfy a thermostat and leave the moisture behind.
Why a bigger unit does not cool a kitchen
A kitchen is not hot because the air conditioning is undersized. It is hot because cooking equipment turns a great deal of energy into heat inside a small space and only part of that heat goes up the hood. Ranges, fryers, griddles, ovens and the dish machine all radiate into the aisle, and every cooler on the line rejects its condenser heat into the same air, which is one reason a badly balanced kitchen shows up first as restaurant refrigeration complaints.
That is also why more cooling is rarely the answer. Cold air delivered into a kitchen is air the hood is entitled to pull straight back out, so a larger unit mostly buys a larger bill. The order that works runs the other way: exhaust and make-up air right first, then the temperature that air arrives at, then cooling where people stand still.
Spot cooling has a real place and a narrow one. A head aimed at the pass or the prep bench cools the person rather than the room, without adding load the hood removes a moment later, and a ductless mini split installation is the usual way it gets done. It is not a substitute for make-up air, and one hung over a fryer battery is money spent on air that leaves through the canopy.
What makes a kitchen unbearable
- Make-up air arriving untemperedA draft in February, humidity in August.
- Cooling aimed where the hood takes itSupply discharged near the canopy is exhausted before anyone stands in it.
- Condenser heat from line refrigerationEvery undercounter unit is a small heater aimed at the aisle.
- Dish machine steam with nowhere to goHeat and moisture in the room least likely to have its own exhaust.
- Radiant heat off the range batteryFelt on the skin, never seen by a thermostat.
Tempered or untempered, and what a Long Island winter does to that choice
Make-up air units come in two broad shapes. An untempered unit is a fan, a filter section and a damper: outside air delivered into the kitchen at whatever the weather is doing. A tempered unit adds heat, usually a direct-fired gas burner in the airstream, and delivers the same volume at a temperature somebody can work beside. Some add cooling for the summer side; plenty of restaurants heat only.
In a mild climate the untempered unit is defensible. Here it is a decision with a season attached. A January morning can put air into a kitchen cold enough that nothing thaws near the discharge, and that air lands on a line where the fryers are already lit. What happens next is predictable. Somebody switches the make-up air unit off to stop the draft, the building goes negative, and every symptom that follows gets reported as an air conditioning problem.
The summer side is quieter and costs more over a year, because untempered air carries Long Island humidity into the kitchen and out through the pass, where it lands on equipment that has to remove it again.
Choosing between them is a survey question rather than a catalog question. It turns on the volume the canopy needs, where the discharge lands relative to where people stand, whether there is gas capacity and a flue route for a direct-fired unit, and what the roof structure will carry. The numbers come off the hood manufacturer's data and the measurements taken on site, which is also where the case for replacing a unit outright gets settled rather than guessed. That work sits under commercial HVAC installation.
One thing worth saying plainly: a make-up air unit that gets switched off is not a make-up air unit. If your kitchen is turning yours off every winter, that is a design or a control problem to solve, not a habit to complain about.
The hood, the fan that serves it, and the switch that ties them together
A canopy hood is a passive part. It has no fan of its own. It is a shape that holds a rising plume long enough for the duct above to take it away, with grease removal filters across the throat. All the work is done by the exhaust fan on the roof, and capture depends on that fan moving what the canopy was designed around.
An interlock is the control that ties the two together, so the make-up air unit starts with the exhaust fan and stops with it. Where one was never fitted, or has since been bypassed, the make-up air unit runs on a switch somebody has to remember, and that switch is the most common reason a properly designed kitchen behaves like a badly designed one. Testing the interlock is a short job on a scheduled visit and it is worth asking for by name when you book commercial HVAC maintenance.
On the exhaust side the checks are ordinary and get skipped anyway: fan rotation and speed, belt condition and tension where the fan is belt driven, whether the hinge kit has been opened since the fan went in, the duct connection at the curb, and where the fan throws its discharge on a roof that has collected equipment over the years.
Exhaust fans, ducted ventilation and general building exhaust across every kind of commercial property are covered under commercial ventilation and exhaust systems, and what a restaurant does to that equipment is the subject here.
Most of the work on a restaurant air balance happens overhead: the canopy, the duct above it, the supply plenum in front of it, and the roof over all three.
What grease-laden air does to everything downstream
Kitchen exhaust is not smoke. It is an aerosol of vaporized fat that condenses on the first cool surface it meets and then collects whatever else is in the airstream. The filters in the canopy take the bulk of it out, and the duct above them is built the way it is because of what gets past.
None of that grease stays where it is wanted. What the filters miss coats the inside of the duct and the fan housing, and a fan wheel carrying an uneven film runs out of balance, wears its bearings and loses the volume the canopy was designed around. Capture falls off with nothing visibly wrong. On the roof, a fan discharging near another unit's outside air intake sends the same aerosol into that unit, where it lands on a filter, then a coil, then a blower wheel, which is an unglamorous reason for a rooftop unit repair on a restaurant that has never needed one before.
Inside the building the same air is what everything else breathes. Return grilles build a film that holds dust, and the duct behind them does the same, which is why commercial duct cleaning comes round faster in a restaurant than in an office of the same age and size.
Washing the grease removal filters on a schedule is the cheapest item on this list and it protects everything after them. Cleaning the grease duct itself is specialist work with its own certification, carried out by a hood cleaning contractor. What we look after is the air side: the fan, the make-up air, the balance between them, and the equipment downstream that the grease reaches.
What brings a restaurant to the phone, and how the work fits around service
Beyond the balance symptoms already covered, three calls come in again and again, and none of the three announces itself early.
Something new went under the hood
A fryer battery or a char grill added to the line, under the same canopy and the same fan. What captured fine last year does not now.
The make-up air unit is off
A tripped breaker, a failed damper motor, or a switch turned off in February that nobody turned back on.
Humidity that will not clear
A clammy room, wet glassware, a smell that stays. Short run time, unconditioned infiltration, or both.
Diagnosis on the air side has one awkward property: a balance problem only shows itself with the kitchen running. A hood that captures beautifully at ten in the morning tells a technician nothing, so the visit that finds the fault is often booked during a service, with somebody on the roof and somebody in the kitchen while the line works.
The repair then goes where it does least damage. Filter and belt changes, damper checks and interlock testing fit between services or before open. Anything that shuts the hood down shuts the kitchen down, so a fan or make-up air unit replacement is scheduled for a closed day or overnight, and rooftop changes bring a crane, a permit and a lift plan built around your trading week.
Emergency work does not wait for a window. Heating and cooling calls are answered around the clock, every day of the year, and the typical on-site response across Suffolk and Nassau County is inside 90 minutes. If the kitchen cannot open, it is an emergency HVAC repair and it goes out now. Scheduled work is booked Monday to Friday, 8am to 5pm.
Restaurant HVAC questions we get asked most
Our kitchen is unbearable in summer. Can you just fit a bigger air conditioner?
It can be done and it usually disappoints. Cooling a kitchen is the last of the three steps and never the first, and a unit sized to out-run a hood raises the bill more than it lowers the temperature. If all three are right and the room is still hot, capacity is the honest answer, and by then you know it rather than hope it.
The front door is hard to open. Is that really an HVAC problem?
Yes. A door that heavy is held by a pressure difference across it, so changing the closer treats the one symptom you can reach and leaves what is causing it. That pull is the cheapest reading you will ever take of your building's balance.
Our make-up air unit gets switched off every winter. What can be done about that?
Find out why first, because the kitchen is not wrong to switch it off. Either the unit is untempered, or it is tempered and the burner, gas valve or discharge control has failed, or the discharge is aimed at a person instead of in front of the canopy. Those are three different repairs, and once the air arrives at a temperature people can work beside, an interlock takes the decision away from the switch.
What does a survey involve, and does it interrupt service?
Time on the roof with the fans and units, time in the kitchen with the hood running, and time in the dining room with the doors doing what they normally do. The measurements that matter are taken with the line lit, so part of it happens while you trade. Nothing comes apart, and you get the findings in plain terms before anything is quoted.
Tell us what the room and the line are doing
Describe the door, the hood and the dining room and you will hear what it most likely is before a truck moves. Working in Long Island kitchens since 1999, with more than 6,000 completed commercial and residential projects behind us.
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