The addition of energy causes evaporation. Cooling causes condensation. And only the droplets that are formed as a result can be mechanically separated. <\/strong><\/p>\n<\/blockquote>\n\n\n\n This very process also plays an important role in commercial kitchens. There, it\u2019s not just water that evaporates. During frying, grilling, baking, and deep-frying, components of oils and fats also partially transition into the gas phase. The rising cooking fumes therefore contain visible aerosols as well as invisible gaseous components. <\/p>\n\n\n\n Evaporated liquids in kitchen ventilation systems<\/strong> therefore pose a particular challenge. As long as they remain in gaseous form, a mechanical aerosol separator cannot capture them in the same way it captures liquid droplets. The exhaust air carries them further, and they can later condense again in air ducts, fans, heat recovery systems, or HVAC units. <\/p>\n\n\n\n Our in-depth technical article on this topic has now been published on the cci Knowledge Portal:<\/p>\n\n\n\n \ud83d\udc49 Vaporized Liquids: The Invisible Danger in Commercial Kitchen Ventilation<\/a><\/strong><\/em><\/p>\n\n\n\n Mnemonic:<\/strong> Water vapor in its gaseous state is invisible. A visible white cloud consists of condensed water droplets and is therefore an aerosol. <\/p>\n<\/blockquote>\n\n\n\n When it comes to kitchen ventilation, we often talk about aerosols. That\u2019s true, because grease and water droplets contaminate the kitchen exhaust air. But aerosols are only part of the overall contamination. <\/p>\n\n\n\n Aerosols consist of solid or liquid particles suspended in the air. These include, for example: <\/p>\n\n\n\n These particles and droplets have a measurable size. A suitable aerosol separator can therefore remove them from the air stream. <\/p>\n\n\n\n In the scientific sense, however, \u201cvapor\u201d refers to the gaseous state of a substance. A gaseous substance consists of individual molecules. These molecules are significantly smaller than an aerosol droplet. For this reason, gaseous components initially pass through a mechanical aerosol separator largely unimpeded. <\/p>\n\n\n\n This means that a range hood can effectively filter out visible grease droplets while still allowing gaseous organic compounds to be carried away with the exhaust air.<\/p>\n\n\n\n We’re familiar with a simple example from the gas station. We can smell gasoline even though we normally can’t see fuel droplets in the air. <\/p>\n\n\n\n The reason is simple: Volatile components of the fuel evaporate. They exist in gaseous form and therefore reach our noses. Nevertheless, a particle measurement in this range may still indicate only a low aerosol concentration. <\/p>\n\n\n\n So the air appears to contain few particles. Nevertheless, it contains gaseous substances. <\/p>\n\n\n\n The same basic principle applies to vaporized liquids in kitchen ventilation systems. A low particle concentration does not automatically prove that the exhaust air is uncontaminated. This is because, in addition to measurable aerosols, gaseous organic compounds may be present. <\/p>\n\n\n\n An aerosol separator that appears clean is often taken as evidence that the exhaust air has been properly cleaned. However, this impression can be misleading. <\/p>\n\n\n\n If a large portion of the contaminants is in gaseous form, it flows past the mechanical aerosol separator. The separator can therefore remain relatively dry and clean. However, this does not mean that the contaminants have disappeared. <\/p>\n\n\n\n The gaseous components are carried by the exhaust air into the downstream system. There, they flow through: <\/p>\n\n\n\n As it travels along this path, the exhaust gas cools down. And that is precisely what triggers the reverse process we see in the cover image. The gaseous components turn back into liquid droplets. <\/p>\n\n\n\n When the temperature of the kitchen exhaust air drops, components that were previously in gaseous form can condense. This results in water films, oily residues, and grease deposits. <\/p>\n\n\n\n Condensation often does not occur in an easily accessible location. It can form anywhere in the downstream exhaust air system\u2014for example, on a cool duct wall, in a duct elbow, or on a heat exchanger. <\/p>\n\n\n\n This can lead to several problems:<\/p>\n\n\n\n The pollution was invisible inside the range hood. It later becomes visible and noticeable in the exhaust duct. So the problem wasn’t solved\u2014it was merely shifted elsewhere. <\/p>\n\n\n\n This relationship is particularly important when exhaust air travels long distances. The longer the exhaust air flows through the system, the more time it has to cool down. And the more it cools down, the greater the likelihood of condensation. <\/p>\n\n\n\n Particle counters are important for evaluating kitchen ventilation. They show how many aerosols are present in the air. In addition, suitable devices can detect particles of different sizes. However, a particle counter cannot detect individual gas molecules. <\/p>\n\n\n\n That is why a particle measurement answers only some of the questions:<\/p>\n\n\n\n However, it does not answer the question of how many additional gaseous organic compounds are present in the exhaust air. A flame ionization detector can be used for this purpose. The abbreviation is FID. Such a device detects gaseous organic compounds and often reports a total carbon (C) value. <\/p>\n\n\n\n It is important to clarify one point: A FID does not simply measure every type of \u201cvapor,\u201d nor does it measure water vapor. Rather, it provides information about organic compounds in the gas phase. This may also include gaseous components derived from heated oils and fats. <\/p>\n\n\n\n Therefore, only the combination of several measurement methods provides a more realistic picture:<\/p>\n\n\n\n Particle measurement<\/strong> indicates aerosol contamination. If you measure only aerosols, you are seeing only part of the kitchen exhaust air. Exhaust air may appear to contain few particles but still contain gaseous organic compounds. <\/p>\n\n\n\n <\/p>\n\n\n\n Odors are often considered merely a comfort issue. However, they can also indicate the presence of gaseous substances in the exhaust air. An exhaust ventilation system may show no abnormalities in a particle measurement and still emit a distinct odor. This is not a contradiction, as many odor-causing substances exist in gaseous form. <\/p>\n\n\n\n Downstream systems such as activated carbon, UV systems, or other odor-control methods may be useful. However, they are no substitute for effective capture and efficient aerosol separation at the source. <\/p>\n\n\n\n In addition, the exhaust air must be pretreated as thoroughly as possible before odor treatment. If water, oils, or fats condense before reaching an activated carbon filter, they can clog its pores and surfaces. This can reduce the filter\u2019s effectiveness while increasing maintenance and cleaning requirements. <\/p>\n\n\n\n Odor treatment should therefore not be used as a last-resort solution for inadequately treated kitchen exhaust air. It must be part of a coordinated overall system. <\/p>\n\n\n\n A range hood doesn’t work well simply because it has a certain exhaust airflow rate. How the air flows is also crucial. Cooking fumes rise due to thermal convection above the cooktop. However, various factors can alter this thermal convection current: <\/p>\n\n\n\n Different flow zones can also form inside the hood. Directional flows, vortices, areas with low flow, and dead zones may develop. <\/p>\n\n\n\n That is why we must clearly distinguish between three processes:<\/p>\n\n\n\n Those are three different steps.<\/strong><\/p>\n\n\n\n A range hood can initially capture cooking fumes. However, the contaminated air has not yet automatically reached the aerosol separator. It can swirl around inside the hood, or it can flow past the separation stage. <\/p>\n\n\n\n Increasing the airflow does not automatically solve this problem. An improperly directed flow can increase turbulence and even worsen the detection. That is why it is not just the flow rate that matters. The quality of the flow direction is just as important. <\/p>\n\n\n\n A look back at our joint cci\/REVEN webinar also shows just how much turbulence and disruptions affect actual data collection:<\/p>\n\n\n\n \ud83d\udc49 Turbulence, vortices, effects\u2014what really happens in a flow<\/em><\/strong><\/a><\/p>\n\n\n\n Condensation isn’t necessarily a bad thing. What matters is where it occurs. Condensation in a hard-to-reach exhaust duct is usually undesirable, because it leads to buildup that is difficult to monitor and clean. <\/p>\n\n\n\n Condensation in the accessible area of a kitchen hood, on the other hand, can be technically beneficial. There, a suitable collection device can capture the newly formed droplets. This is precisely where the principle of controlled or forced condensation comes into play. <\/p>\n\n\n\n An induction hood directs an additional airflow specifically into the interior of the hood. This induction airflow is generally cooler than the rising thermal current. <\/p>\n\n\n\n When the two air streams mix, the temperature of the contaminated air drops. Under suitable conditions, gaseous components may condense as a result, either before reaching the aerosol separator or within it. <\/p>\n\n\n\n Small liquid droplets form again from the gas phase. And only then can a mechanical aerosol separator remove these substances. <\/p>\n\n\n\n The key advantage lies in the location of the condensation. It should take place, as much as possible, where the system is designed for separation, drainage, cleaning, and maintenance. <\/p>\n\n\n\n So the question is not just:<\/p>\n\n\n\n Is condensation occurring?<\/strong><\/p>\n\n\n\n The more important question is:<\/p>\n\n\n\n Where does it take place? In a controlled manner within the kitchen hood, or in an uncontrolled manner in the downstream exhaust system? <\/strong><\/p>\n\n\n\n The technical approach, therefore, is not to prevent all condensation. It is to redirect the condensation to a suitable and controllable location. <\/p>\n\n\n\n An induction hood doesn’t work well simply because it blows air into the hood. The design must direct the airflow in a targeted manner. That’s why several factors must work together: <\/p>\n\n\n\n An incorrectly configured induction current can cause turbulence. It can adversely affect the cooking vapor and impair detection. <\/p>\n\n\n\n That is why the manufacturer must investigate the specific flow effects. CFD simulations can help with this, as they reveal vortices, dead zones, and flow paths. However, a CFD visualization alone does not prove that the design will function properly. <\/p>\n\n\n\n Effective product development therefore combines several methods:<\/p>\n\n\n\n Only the combined effect of these processes reveals whether a specific range hood actually stabilizes cooking fumes, directs them to the separator, and achieves the desired cooling effect.<\/p>\n\n\n\n We have summarized the current expert discussion on induction hoods, airflow rates, room supply air, airflow patterns, and condensation in detail in a separate blog post:<\/p>\n\n\n\n \ud83d\udc49 Criticism of Induction Range Hoods: Facts, Measurements, and Unanswered Questions<\/em><\/strong><\/a><\/p>\n\n\n\n Our position is clear: Criticism of induction hoods is important and legitimate. However, it must take into account the specific design. Furthermore, it must explain how the initial pollution caused by gaseous water, oil, and grease components should be treated as an alternative. <\/p>\n\n\n\n After all, the fumes don’t just disappear simply because you reject a particular technical solution.<\/p>\n\n\n\n A modern kitchen ventilation system must do more than simply move a certain volume of air. It must capture, transport, treat, and remove the pollutants from the system in as controlled a manner as possible. <\/p>\n\n\n\n Planners, plant builders, and operators should therefore answer the following questions:<\/p>\n\n\n\n The sooner these questions are addressed during the planning phase, the lower the risk that the damage will only become apparent later in a hard-to-reach area.<\/p>\n\n\n\n The illustrations in this blog post are taken from our reference book:<\/p>\n\n\n\n “Misconceptions in Ventilation Technology and Air Quality Control”<\/strong><\/p>\n\n\n\n The book explains common misconceptions about aerosols, gases, vapors, odors, flow, separation, and measurement techniques. It uses many simple examples and clear illustrations. <\/p>\n\n\n\n For more information, see our blog post:<\/p>\n\n\n\n\n
Aerosols and vapors are not the same thing<\/h2>\n\n\n\n\n
![\"Mechanical](\"https:\/\/www.reven.de\/wp-content\/uploads\/2026\/08\/REVEN_Buch-Abbildungen.001-1080x608.jpeg\")
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Exhaust air can be low in particles but still contaminated<\/h2>\n\n\n\n![\"Gaseous](\"https:\/\/www.reven.de\/wp-content\/uploads\/2026\/08\/REVEN_Buch-Abbildungen.002-1080x608.jpeg\")
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The aerosol separator can remain clean<\/h2>\n\n\n\n\n
The buildup is visible in the exhaust duct<\/h2>\n\n\n\n\n
![\"Condensation](\"https:\/\/www.reven.de\/wp-content\/uploads\/2026\/08\/REVEN_Buch-Abbildungen.003-en-GB-1080x608.jpeg\")
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Why Particle Measurement Alone Is Not Enough<\/h2>\n\n\n\n\n
FID measurement<\/strong> indicates gaseous organic contamination.
Temperature measurement<\/strong> indicates potential condensation areas.
Flow measurement<\/strong> indicates where the contaminated air actually goes.<\/p>\n\n\n\n![\"REVEN](\"https:\/\/www.reven.de\/wp-content\/uploads\/2026\/08\/REVEN_Buch-Abbildungen.004-en-GB-1080x608.jpeg\")
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Odors are an important warning sign<\/h2>\n\n\n\n
Flow Determines the Effect<\/h2>\n\n\n\n\n
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![\"simple](\"https:\/\/www.reven.de\/wp-content\/uploads\/2026\/08\/REVEN_Buch-Abbildungen.006-en-GB-1080x608.jpeg\")
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Redirecting Condensation to the Right Place<\/h2>\n\n\n\n![\"induction](\"https:\/\/www.reven.de\/wp-content\/uploads\/2026\/08\/REVEN_Buch-Abbildungen.005-en-GB-1080x608.jpeg\")
An induction range hood isn’t necessarily a good choice<\/h2>\n\n\n\n\n
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Planners and operators should ask these questions<\/h2>\n\n\n\n\n
Learn More in the REVEN Reference Book<\/h2>\n\n\n\n