https://vedard.com/blog/common-faults-and-solutions-for-smoke-exhaust-fans/
Source: https://vedard.com/blog/common-faults-and-solutions-for-smoke-exhaust-fans/
Date: 2025/12/01
https://vedard.com/blog/common-faults-and-solutions-for-smoke-exhaust-fans/
First, clarify: what exactly is the function of a fire exhaust fan?
Don’t think that installing a fan solves everything. You need to know what problems it can solve before you understand why you need to keep an eye on it and fix it as soon as it breaks down.
1. Remove toxic fumes to preserve the “safe air” we breathe.
When a fire breaks out, whether it’s wood, plastic, or electrical appliances, it releases lots of toxic gases—carbon monoxide with colorless and odorless, and can cause dizziness and unconsciousness. Hydrogen sulfide smells like rotten eggs and is highly toxic; and there’s hydrogen cyanide, even a tiny amount can be fatal. These gases are lighter than air and rise, ending up at breathing height. If they can’t be expelled, a person inside won’t last more than 3-5 minutes before losing consciousness. The primary function of a smoke extraction fan is to quickly remove these toxic fumes.
2. Blow away the thick smoke to make escape routes visible.
The biggest problem with thick smoke, besides being toxic, is that it obstructs vision—visibility at a fire scene is often less than 1 meter. Even if you walk the same road every day, you can still bump into walls, slip and fall in the dark, or even run into the fire instead of heading for the safety exit.
With the ventilation system activated, the smoke concentration decreased, and visibility increased to 5-10 meters. People could clearly see the green lights indicating safety exits, and firefighters no longer needed to grope around in the smoke to find the source of the fire and rescue people. Previously, a fire broke out on the third floor of a shopping mall. The ventilation system was activated in time, and the smoke quickly dissipated, allowing all customers to evacuate within 10 minutes. In contrast, the adjacent warehouse, which did not have ventilation systems, was completely blocked by smoke. Firefighters searched for trapped people for more than 20 minutes, and those who were rescued suffered lung injuries from smoke inhalation.
3. Remove the hot smoke to slow the spread of the fire.
The temperature of smoke in a fire can reach 500-800℃. Fans remove the high-temperature smoke, lowering the fire temperature by 100-200℃. This makes combustibles less easily ignited, slowing the spread of the fire. For example, in a factory fire, with fans running, the fire can be contained around the ignition point, giving firefighters 15-20 minutes to extinguish it; without fans, the fire could spread throughout the entire factory in 5 minutes, doubling the losses.
II. Six common faults of smoke exhaust fans, and step-by-step instructions on how to troubleshoot and resolve them.
When a fan malfunctions, you don’t need to call a repairman right away. Many minor problems can be solved by checking them yourself step by step in just a few minutes. The key is to find the root cause of the problem.
1. If the fan won’t start even when the manual button is pressed on-site—first check the “gear setting” and “electrical” settings.
This is the most common problem; 90% of the time it’s not a faulty fan, but a minor issue with settings or power supply. Check these 4 steps:
Step 1: First, check the “gear” on the fan control cabinet. The control cabinet usually has two gears: “manual” and “automatic”. If it’s set to “automatic”, the manual button won’t work. Switch it back to “manual” and try pressing the button again.
Step 2: Check if the control cabinet has power. There is a power indicator light on the control cabinet. If it is not lit, it means there is no power. Turn on the main switch. If the light is on but it still doesn’t start, use a multimeter to check if there is power on the three phases (live wire). It is likely that the wire connection is loose. Tighten it again.
Step 3: Check the “small parts” in the control cabinet. Open the control cabinet door and check if the circuit breaker (air switch) has tripped. If it has, reset it. Then check the contactor (the small square with wires). If the contacts are burnt black, the contactor is broken. Replace it with the same model. It usually only costs a few tens of yuan.
Step 4: Finally, check the “motor”. If everything else is fine, listen for a “humming” sound from the motor when you press the button. If there is a sound, it means the motor is stuck (for example, the impeller is tangled with debris). Disassemble the fan and clean it. If there is no sound, the motor is burnt out. You need to find a professional to repair it. Don’t try to disassemble it yourself.
2. Fire control room cannot be remotely started – focus on checking the wiring and unlocking mechanisms.
If you press the button in the control room and the fan doesn’t respond, it’s either a problem with the remote system or a conflict with the on-site speed setting. Follow these 5 steps:
Step 1: First check the “remote line”. There is a dedicated line from the control room to the fan control cabinet. It may have been chewed through by rats, or the connector may be loose. Use a multimeter to check if the line is continuous. If it is broken, connect it; if it is loose, tighten it.
Step 2: Check the “multi-line control panel” in the control room. The control panel has “manual disable” and “manual enable”. If the “disable” light is on, press the unlock button to change it to “enable”. Then check if the button is pressed down and does not spring back, or if the button is broken. Try replacing the button.
Step 3: Check the “Switching Module”. The control panel and the fan rely on the switching module to transmit signals. If the module’s wiring is loose or the module itself is faulty, it will not be able to transmit signals. Replace the module or tighten the module’s wiring again.
Step 4: Check the “gear” of the field control cabinet. Remote control requires the control cabinet to be in “automatic” mode. If it is in “manual” mode, remote control is useless. Go to the field, switch the gear to “automatic” mode, and then go back to the control room to test it.
Step 5: Finally, check the fan itself. If everything else is fine, then the problem lies with the fan or control cabinet. Check the motor and contactor using the same method as for the first fault.
3. If the ventilation fan does not start automatically during a fire – first check if the “automatic start” setting is on.
Automatic activation relies on the linkage of the fire alarm system. If it fails to activate, it’s most likely due to incorrect system settings. Check these 6 steps:
Step 1: Check the “status” of the fire alarm control panel. The control panel has “automatic prohibition” and “automatic permission”. If it is on “prohibition”, simply switch it to “permission”. This is the easiest step to forget.
Step 2: Check the “interlocking lines”. Check the wires from the controller to the fan control module for breaks or looseness. Use a multimeter to test for continuity. Repair the wires if there are any problems.
Step 3: Check the “control module”. If the module is faulty, the signal cannot be transmitted. Replace it with a new module, or unplug and replug the module’s power supply. Sometimes the module may have crashed.
Step 4: Check if the “linkage formula” is correct. For example, if the fan should only start when both the smoke detector and the heat detector alarm simultaneously, but the formula is written as “smoke detector or heat detector”, or the fan module is not included in the formula, you need to find a fire protection maintenance person to rewrite the formula. Don’t try to change it yourself.
Step 5: Check the on-site control cabinet settings. The same issue remains: it must be in “automatic” mode. Manual mode with automatic linkage won’t work. Go to the site and adjust the settings accordingly.
Step 6: Check for fan and control cabinet malfunctions. If everything else is fine, then the equipment is broken. Repair the motor and contactor using the method described in Step 1.
4. If the fan vibrates excessively when running, it’s most likely a problem with the impeller or bearings.
Excessive vibration is not only noisy, but it can also loosen fan screws, dislodge air ducts, and even damage the motor. The reasons are mainly in these 5 areas:
Impeller deformation/imbalance: If the fan has been stored for a long time, the impeller may be deformed by impact, or too much dust and oil may have accumulated on the blades, making one side heavier than the other, causing it to shake when rotating. Solution: Disassemble the casing and check if the impeller is bent. If it is bent, replace it. If it is dusty, clean it with a brush. After brushing, rotate it by hand to check if it rotates evenly. If it is uneven, use a balancer to adjust it.
Bearing wear/loosening: Over time, the bearings in the motor wear down, the balls wear out, and the clearance increases, causing the motor to wobble. Solution: Remove the motor end cover and check the bearing for rust or debris. If it’s damaged, replace it with the same model. When replacing, add a spoonful of grease (don’t add too much, as it will cause overheating).
The fan shaft and motor shaft are not concentric: They were not aligned during installation, and the two shafts are not on the same line, causing them to wobble and vibrate when rotating. Solution: Loosen the motor’s fixing screws and move the motor in the direction of alignment, measuring with a ruler as you move it, until the two shafts are aligned, then tighten the screws.
Loose screws: The positioning screws of the impeller, the clamp screws, or the foundation bolts of the fan base may be loose, causing the fan to wobble when turned. Solution: Use a wrench to tighten all the screws, especially the foundation bolts, until they are completely tightened and cannot be wobbled by hand.
The blades are faulty: if one side of the blade is thicker than the other, or if one blade is worn, it will be unbalanced. Solution: Replace the worn blade, or clean the debris off the blade and then rebalance it.
5. The fan is making a lot of noise when it’s running – first check for “friction” and “bearings”.
Loud noise not only disturbs neighbors, but it can also be a sign that equipment is about to break down. There are three common causes, which are easy to solve:
Impeller and casing friction: A deformed impeller, loose screws, or a misaligned casing can cause the impeller to rub against the casing when it rotates, producing a “squeaking” friction sound. Solution: Check if the impeller is bent; replace it if it is; tighten loose screws; adjust the casing position to ensure a uniform gap between the impeller and the casing (generally 3-5 mm) to prevent rubbing.
Bearing wear/large clearance: A damaged bearing will make a “humming” noise when it rotates; the larger the clearance, the louder the noise. Solution: Replace the bearing. When replacing it, add grease, but don’t add too much.
Too high a speed: If the fan speed exceeds the rated value, it will also be noisy. Solution: Check if the motor speed matches the fan speed. If the motor is running too fast, replace it with a low-speed motor, or have an electrician adjust the frequency converter (this requires a professional).
6. The fan is running, but the smoke extraction effect is poor—either it’s “too small” or there’s “air leakage.”
The most troublesome thing is that the fan is running, but the smoke can’t be expelled, or it’s expelled very slowly. The reasons are mostly in these 5 areas:
The fan was undersized: The initial smoke extraction capacity was miscalculated. For example, a 500-square-meter garage should have had a 30,000 m3 /h fan, but a 20,000 m3 /h fan was chosen instead , resulting in insufficient suction power. Solution: The only solution is to replace the fan and recalculate based on “smoke extraction capacity = area × unit smoke extraction capacity”. For underground garages and shopping malls, calculate at 60 m3 /h per square meter; for offices , calculate at 40 m3 /h per square meter; and for kitchens, calculate at 80 m3 /h per square meter.
Air leakage in the duct: If the duct joints are not properly sealed or have cracks, the smoke drawn by the fan will leak out through the gaps, reducing the actual smoke extraction volume. Solution: Seal all joints and cracks in the duct with fire-retardant sealant; also seal the holes in each floor slab of the vertical duct (connecting to the roof) with fire-retardant material to prevent smoke from spreading to other floors.
Too many bends or too narrow ducts: If the duct has several right-angle bends or the pipe diameter is too small, the air resistance is high, and the smoke cannot be expelled properly. Solution: Try to make the duct straight, and use rounded elbows for bends; if the pipe diameter is not large enough, replace it with a larger one, for example, replace the original 300mm pipe with a 400mm pipe.
Inadequate smoke control measures: Smoke curtains are not installed in smoke control zones (e.g., glass smoke curtains are not installed in shopping malls), allowing smoke to escape to other areas, causing smoke to escape from one area while smoke from another is being released. Solution: Install smoke curtains according to regulations, at least 50 centimeters high, to block the smoke and prevent it from spreading.
The smoke exhaust/air supply vent is in the wrong location: the smoke exhaust vent is facing a wall or blocked by something, preventing smoke from being drawn in; the air supply vent is not open, or is open too small, preventing fresh air from entering and smoke from being expelled. Solution: Clear away any debris in front of the smoke exhaust vent and position it facing an open area; open the air supply vent to a sufficient size to allow fresh air to enter and create convection.