Why is my AC Unit Sweating Inside?

If you’ve ever noticed beads of water collecting around an air conditioner system or pipes, or seen water slowly dripping from your AC unit then you’ve likely experienced the dreaded 'air conditioner sweat'. While a small amount of condensation on an ac system is normal, dozens of droplets or water drips certainly is not - and can often indicate a bigger problem with your system. If you've noticed some droplets on your unit and are curious as to whether this is normal or problematic - read on to learn more.

What is air con sweat?

Air conditioner sweat is condensation that occurs when warm, moist air comes into contact with the cold surface of an AC duct. Air conditioner sweat happens when the air temperature is below the dew point temperature. The dew point temperature is the temperature at which water vapour will start to form.

The excess moisture - or air conditioner sweat - created can also lead to damage to your walls, termites and mould.

When should I worry about condensation on air conditioning ducts?

Firstly, the question that needs to be asked is why is your air conditioner in contact with warm, moist air when the room should be cooled by the air conditioner?

The answer can be a variety of reasons. Often, air conditioner sweat can be harmless and could be something as simple as a window left cracked open, letting in outside air. But, sometimes air conditioner swear can be a symptom of something more serious issue in your HVAC system.

To help you identify what’s causing your air conditioner to sweat and to figure out how to rectify the problem, read through the points below.

Reasons why your air conditioning system may be sweating.

Humid Air

Though you may not be aware of them, if your air conditioner duct is sweating there may be a chance that there is a small space or cracks in the room where outside air can creep in. This is especially true if you live in a humid area.

If you’re experiencing AC sweat, then a good place to start is by checking for small gaps where outside air can enter. When the hot, humid air mixes with the cold air of the AC unit, condensation forms.

If the condensation is caused by outside air getting in, then the fix is relatively simple - obstruct the outside air from entering. If you’re unable to seal up the gaps you can try placing a fan in the room, this will circulate air flow around to keep it cooler.

Low Temperature Setting

To understand how temperature can affect condensation, you must first understand what relative humidity is. Put simply, relative humidity is a figure that says how much water vapor is in the air, compared to how much it could hold at that temperature. You’ve probably seen this on a weather channel when the percentage of humidity in the forecast is shown.

For each relative humidity percentage, there is a value below that figure where condensation will start. So, if you live in a humid area and set your ducted air conditioner unit to a low degree, it’s likely to form condensation - or AC sweat. This type of AC sweat isn’t a problem but can cause damage to walls when it drips.

Restricted Air flow

There are a number of ways in which air flow can be restricted, these include a blocked duct, a backed-up condensation line, dirty filters or frozen evaporator coils. When airflow is reduced, the temperature of the air goes below the dew point and causes sweating.

In this case, the AC sweating is a symptom of another problem with your unit. It’s best to get an air conditioning technician in to find exactly what is wrong with the system so that it can be fixed and your AC can be restored to its full potential.


When an aircon duct is installed without the correct amount of insulation, it can be the cause of the air conditioning sweat. Insulation can help to prevent sweating because it reduces the temperature of the vents and ducts.

Without insulation, the vents and ducts can become very cold when the AC unit is running and will cause the surrounding air to collect in the ducts and cause condensation.

Alternatively, too much roof insulation can cause a room to become too warm, which can also cause sweating.

A good technician will be able to advise you about how thick the insulation should be for the area you’d like to install a duct.

Plugged Drain Line

A plugged drain line can have a devastating effect on a house and in extreme cases, even cause the roof to cave in.

Air conditioners have a drip tray that catches condensation from the humid outside air and drains the water droplets down through condensation lines and out of your room. A drain line can become plugged for a variety of reasons, like getting debris, dust, hair or grime caught in the line, which can block the water from draining out.

When this happens water can build up in the ceiling. In minor cases, homeowners will just experience a small drip. However, if your ceiling is dripping near an aircon vent it’s important to take this as a warning sign and call an HVAC technician. If too much water builds up, then the weight and pressure can cause the ceiling to collapse.


While we've touched on some common possible causes for AC sweat, there are many more problems that can be the reasons for condensation in your ducted air conditioner. While some condensation can be harmless and is to be expected, sometimes it can indicate an imminent problem.

Much like when a unit is blowing out hot air or frozen over, sweat on an air conditioner unit can be a symptom of something bigger. If your unit is dripping water out of it, then the sooner you call a technician to come and check it out, you'll likely save a lot of money. If you wait too long the problem may get bigger and end up costing a lot more in the long run.


Is it normal for an air conditioner to sweat?

Mild condensation on an AC unit shouldn’t be too much of a cause for concern. In fact, a small amount of condensation on a running air conditioner is completely normal.

However, if the sweating is very obvious then it could well be a sign that there’s a problem with your system. So, to be safe, if you notice any condensation on your unit, it’s a good idea to get it checked out by a professional.

How much water condensation from AC is normal?

As outlined in the information above, in a healthy air conditioning unit, the amount of condensation can directly be correlated to the humidity of your environment. If the air is more humid, more condensation can be expected.

Even in a non-humid environment, small beads of sweat on your air conditioner are normal. But, if your AC unit is dripping any water down walls and/or onto the floor, then this is a sign of a problem and can signify that it’s time to call a professional.

Time to call the experts?

If you are still having issues - it's time to call in the experts. Our Brisbane-based air conditioning repairs team are on hand to give you the assistance you need. Call us on 07 3283 5566 or fill out a quick quote to get your air con back up and running!

Experiencing other air conditioner issues?

Check out our other guides on common problems below:

My air conditioner heat mode is not working

My air conditioner will not turn off

My air conditioner is making a loud buzzing noise

My air conditioner is not turning on

My air conditioner is icing up

My air conditioner is blowing hot air

My air conditioner is leaking water

My air conditioner smells bad

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