It might seem like magic!

Unfortunately, it’s not because we shrunk a wizard and put them in your roof-cavity to make your home less humid.

So does ventilation reduce humidity? The short version is that bringing fresh, dryer air inside effectively dilutes the old, moist air inside your home. 

The longer explanation for why ventilation makes your home less humid is a little more complex and boils down to physics. Let’s take a look at how humidity works. To get started, we need to know that there are multiple ways to measure humidity.

• Relative humidity (RH) refers to how full of moisture the air is as a % (much like how full a cup is) and is how you ‘feel’ humidity.
• Absolute humidity (AH) simply refers to the amount of moisture in the air (a bit like how many ml are in a cup), measured in g/m3.
• Air temperature also contributes to humidity, as it influences how much moisture the air can hold (it changes the size of the cup).

Imagine your air is a set of cups;

Humidity is represented by how full they are. On a hot humid NZ summer day, two cups are 80% full (80% RH). Cup one is at 25°C (your inside temperature), and cup two is 20°C (your outside temperature). Cup two is smaller, due to the temperature difference, and even though both are 80% full cup two is holding less water (AH). Bringing fresh air into your home is like pouring the water from cup two back into a 25°C cup (cup three). If you did this, you would see that cup three would only be 58% full (RH). This is because it only contains 11.69g/m3 of water (AH), compared to cup one which contains 15.97g/m3 of water.

How does this relate to ventilation?

Essentially, the air’s capacity for moisture increased without increasing the amount of moisture inside, thus lowering the relative humidity. By bringing in fresh 20°C air to your 25°C home, you would be able to reduce your indoor humidity by a staggering 22%. But what does this look like? You could open a window, however sometimes there are very valid reasons to want to keep your doors and windows shut. Fortunately, home ventilation systems are here to help provide fresh air to your homes, without the noise and bugs of summer.

So how does ventilation reduce humidity? By harnessing the magic of physics (cool air being drier than warm air) you can bring in cooler drier air over summer. A SmartVent system with a summer feature add-on does this all for you by sensing when the temperature outside is cooler than inside, so you automatically get to enjoy a more comfortable and less humid home this summer.

Want to make your home less humid over summer? Book a free home consultation now!

Side note: Ventilation wizardry works in winter as well! Look out for our next blog post where you can learn about dew point and condensation.