Home / Duct Cleaning / Guide
Duct cleaning - diagnosis
Condensation forming on or around an extraction system, and the damp it causes, is a sign worth reading - because it points to warm, moist air meeting cold surfaces where it should not, which usually means an insulation, airflow or design issue. Left alone, the damp can cause its own problems. Here is what condensation and damp around extraction means, and why it is worth diagnosing.
The short answer
Condensation and damp around an extraction system mean that warm, moist air is meeting a cold surface and condensing - the water vapour in the air turning to liquid where the air is chilled below its dew point. Kitchen extract air is warm and laden with moisture (steam from cooking), so where that air, or the ductwork carrying it, meets a cold surface - a cold duct running through an unheated space, a poorly insulated section, a cold spot - condensation forms. It usually points to one of a few underlying issues: inadequate insulation (letting the duct or air get cold enough to condense), airflow problems (air moving too slowly or cooling too much), or a design issue (ductwork routed through cold spaces without proper provision). The damp it produces is worth addressing because it can cause corrosion of the ductwork, drips and water damage, and encourage mould and hygiene problems. So condensation and damp around extraction is a sign to diagnose - reading it back to the underlying insulation, airflow or design cause, and fixing that, rather than just wiping up the water.
What condensation is telling you
Condensation forms when warm, moist air meets a surface cold enough to chill it below its dew point - the temperature at which the water vapour the air holds turns to liquid. Warm air can hold a lot of moisture; when it is cooled, it can hold less, and the excess condenses out as liquid water on the cold surface. This is the same process as condensation on a cold window in a warm room. So wherever condensation appears, it is telling you that warm, moist air is meeting a surface cold enough to condense the moisture out of it - that is the basic message of any condensation.
Around an extraction system, this has a particular relevance because kitchen extract air is both warm and very moist - it carries the heat and the steam from cooking, so it is laden with water vapour. This warm, moist air is exactly the kind that readily forms condensation when it meets a cold surface. So condensation around extraction is telling you that this warm, moist extract air, or the ductwork carrying it, is meeting a cold surface somewhere and condensing. The question the condensation raises is where and why the cold surface is - because in a well-designed, well-insulated system, the extract air and ductwork should not be meeting surfaces cold enough to condense significantly. So the condensation is a sign that something is letting the air or duct get too cold - which points to an underlying issue worth diagnosing. Reading the condensation means asking what is providing the cold surface it is forming on.
What it usually points to
Condensation and damp around extraction usually point to one of a few underlying issues, all to do with the extract air or ductwork getting colder than it should. The most common is inadequate insulation. Ductwork carrying warm, moist air through a cold space - an unheated void, a cold roof space, outside - needs insulation to keep the duct surface from getting cold; without adequate insulation, the duct gets cold, and the warm moist air inside condenses on the cold duct wall, or the cold outer surface condenses moisture from the surrounding air. So condensation often points to insulation that is missing, inadequate or damaged where the duct runs through a cold space.
Other causes relate to airflow and design. Airflow problems can contribute: air moving too slowly, or a system not running when it should, can let the air and duct cool more than they would with proper airflow, promoting condensation. And design issues can be at the root: ductwork routed through cold spaces without proper insulation or provision, cold bridges, or a design that lets warm moist air reach cold surfaces, builds condensation in from the start. So the condensation, read as a sign, points back to one of these - inadequate insulation (most commonly), airflow problems, or a design issue - as the reason the extract air or duct is getting cold enough to condense. Diagnosing which is the underlying cause is the key to fixing it, rather than just dealing with the water. The condensation is the symptom; the insulation, airflow or design issue is the thing to find and address.
Why the damp matters
The damp that condensation produces is worth addressing, not ignoring, because it can cause a series of problems as it accumulates. Corrosion is one: persistent water on and in the ductwork can corrode the metal over time, degrading the ductwork and shortening its life - a system that is constantly damp inside or out will deteriorate faster than a dry one. Water damage is another: condensation can drip from the ductwork onto surfaces, equipment or the fabric of the building below, causing staining, damage and the nuisance of dripping water where it should be dry. So the damp is not just an aesthetic issue but can physically damage the ductwork and its surroundings.
And condensation and damp encourage mould and hygiene problems: persistent moisture supports mould growth on and around the ductwork and the surfaces it dampens, which is a hygiene concern - particularly around a kitchen or food area - as well as unsightly and potentially affecting air quality. So the damp from condensation brings corrosion, water damage and mould, all of which are reasons to address it rather than tolerate it. These consequences are why condensation around extraction is worth taking seriously as a sign: it is not just water to wipe up, but a symptom of an underlying issue that is also causing ongoing damage and hygiene problems. Left unaddressed, the condensation continues, and the corrosion, damage and mould continue with it. So the damp matters both as a sign to diagnose and as an active problem to stop - which points to fixing the underlying cause, so the condensation stops forming in the first place.
Diagnosing and fixing it
The right response to condensation and damp around extraction is to diagnose and fix the underlying cause, rather than just repeatedly dealing with the water. Since the condensation points to warm moist air meeting a cold surface, the diagnosis is to find where and why that is happening - which cold surface the air is condensing on, and why it is cold. Most often this leads to inadequate insulation on ductwork running through a cold space, which is addressed by insulating the duct properly so its surface no longer gets cold enough to condense. Where the cause is an airflow or design issue, the fix addresses that - correcting the airflow, or the routing or provision that lets the air reach cold surfaces.
Fixing the underlying cause is what actually stops the condensation, because it removes the cold surface (or the exposure of warm moist air to it) that the condensation depends on. Just wiping up the water, or dealing with the damp symptoms, leaves the cause in place, so the condensation keeps forming and the corrosion, damage and mould keep developing. So the sensible approach is to read the condensation as the sign it is - warm moist air meeting a cold surface, pointing to insulation, airflow or design - and to diagnose and correct that cause. This connects to the system's design and maintenance: proper insulation and sound design prevent condensation, and keeping the system running and maintained supports the airflow that helps avoid it. So condensation and damp around extraction is a sign worth diagnosing properly - it points to a fixable underlying issue, and fixing that stops both the condensation and the damage it causes, rather than leaving you endlessly mopping up a symptom.
The takeaway
Condensation and damp around an extraction system mean warm, moist air is meeting a cold surface and condensing - the water vapour turning to liquid where the air is chilled below its dew point. Kitchen extract air is warm and laden with moisture, so where it or its ductwork meets a cold surface, condensation forms. It usually points to one of a few underlying issues: inadequate insulation (most commonly, letting the duct get cold where it runs through a cold space), airflow problems (air cooling too much), or a design issue (ductwork routed through cold spaces without proper provision). The condensation is a symptom; one of these is the cause.
The damp it produces is worth addressing because it can corrode the ductwork, cause drips and water damage, and encourage mould and hygiene problems - ongoing damage that continues while the condensation does. So the right response is to diagnose and fix the underlying cause, rather than just wiping up the water: find where and why the cold surface is, and correct it - most often by insulating the ductwork properly, or by addressing the airflow or design issue at the root. Fixing the cause stops the condensation, and the corrosion, damage and mould with it. So read condensation and damp around extraction as the sign it is - warm moist air meeting a cold surface, pointing to a fixable insulation, airflow or design issue - and address the cause, not just the symptom.
Questions
That warm, moist air is meeting a cold surface and condensing - the water vapour in the air turning to liquid where the air is chilled below its dew point. Kitchen extract air is warm and laden with moisture from cooking, so where it or its ductwork meets a cold surface, condensation forms. It is telling you something is letting the air or duct get cold enough to condense.
One of a few underlying issues: inadequate insulation (most commonly - ductwork running through a cold space without enough insulation gets cold, so the warm moist air condenses on it); airflow problems (air cooling too much, or the system not running when it should); or a design issue (ductwork routed through cold spaces without proper provision). Diagnosing which is the cause is key to fixing it.
Because it can cause several problems as it accumulates: corrosion of the ductwork (persistent water degrades the metal over time), water damage (condensation dripping onto surfaces, equipment or the building fabric), and mould and hygiene problems (persistent moisture supports mould growth, a concern especially around a food area). So the damp is not just water to wipe up but an active problem worth stopping.
No - that leaves the underlying cause in place, so the condensation keeps forming and the corrosion, damage and mould keep developing. The right response is to diagnose and fix the cause: find where and why the cold surface is that the air is condensing on, and correct it - most often by insulating the ductwork properly, or by addressing the airflow or design issue at the root. Fixing the cause stops the condensation.
By proper insulation and sound design - ductwork carrying warm moist air through cold spaces needs adequate insulation to keep its surface from getting cold enough to condense, and the routing and design should avoid exposing the warm moist air to cold surfaces. Keeping the system running and maintained supports the airflow that also helps avoid condensation. So prevention is mainly insulation and design, supported by good airflow.
Yes - persistent water on and in the ductwork can corrode the metal over time, degrading the ductwork and shortening its life; a system constantly damp will deteriorate faster than a dry one. This is one reason to address condensation rather than tolerate it - beyond the drips and mould, it is physically damaging the ductwork, so stopping it protects the system as well as the surroundings.
Condensation and damp point to insulation, airflow or design issues - and the damp can corrode ductwork and grow mould. We clean and inspect ductwork, helping identify the issues behind the damp.
