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  • Writer's pictureAdam Clark

How Dirty HVAC Ducts Can Contribute To Mold Growth.

Indoor air quality is often referred to as a “mold city” because of the potential for mold growth in homes and businesses with poor ventilation. Home humidity levels, temperature, moisture content of the building materials, and pollutants from outside sources can all contribute to mold growth. That being said, while mold can grow in many places other than crowded living rooms and basements, it is less likely to do so in a duct system than you might think. While it is true that moisture condenses on the exterior of a humidifier and leads to condensation inside the humidifier chamber, this does not indicate that mold grows in damp areas or that heat from a furnace or air conditioner will increase the risk of mold growth in homes. The moisture evaporates quickly out of the humidifier and into vents where it should be thinned out by other household appliances.

How Dirty HVAC Ducts Can Contribute To Mold Growth

Similarly, while carbon monoxide from a faulty furnace may build up as CO2 in damp spaces or as CO in ventilated areas, CO does not grow much when released outside through windows and doors as CO gas. On top of all this, when walls are constructed without primary air flow passages (e.g., attics), moisture passes directly through them into dryer cavities where forced-air heating or cooling systems are installed. In other words: Dryer ducts only add moisture to what is already there; they have little impact on indoor air quality without good ventilation.

What to look out for when inspecting homes with HVAC systems.

Inspecting homes with HVAC systems can be challenging due to their complexity and the amount of moving parts inside. It can be difficult to tell at first glance whether something is working properly or not. In addition, the differential pressure between a humidifier and its housing can be difficult to detect, especially if the humidifier is on a stand or is located in a room with low humidity. Opt for the most accurate humidity level detectors on the market. Choose digital controllers with large graphic displays that are easy to read and understand. Be sure to check manufacturer warranties against competitors’ products to ensure high-quality equipment. Humidity sensors are often mounted in a humidifier to help avoid false readings and measurement uncertainty due to moisture from humidifier emissions. Another thing to look for is direct current (DC) equipment. Some humidifiers use an electrical current to keep the water moist, but most use a combination of DC and gas to maintain moisture. Make sure the humidifier is DC/gas or AC/DC. Additionally, pay particular attention to humidifier filter instructions. Some humidifiers use smaller, cheap-o filters that can lead to water damage and a build-up of harmful contaminants.

How to detect mold growth in your home

Most humidifier sensors are programmable and can be set to turn on the humidifier when humidity reaches a certain level. This is a good thing since most people have different WIPA preferences and levels of comfort while living in a home. However, if you are not comfortable turning on the humidifier for long periods of time, you can always set the humidifier to “low” exhausting yourself with the high setting. However, keep in mind that high humidifier settings can be problematic as they can lead to mold growth in areas with high humidity. You can also use a hygrometer to test for humidity. A hygrometer measures air temperature, moisture content, and relative humidity to help you know when to open the humidifier. A hygrometer is usually a cheap-o device that can be found at hardware stores. You can also use an online hygrometer to help with indoor air quality monitoring.

Why mold growth is uncommon in homes with good ventilation

There are many factors that contribute to mold growth in homes. While some causes are similar in all homes, others are specific to certain types of homes and areas. For example, areas with high moisture content, a damp basement, and an air circulation system that cannot move air out of the room easily are more likely to experience mold growth. Mold growth is more likely to occur in rooms with poor ventilation. That said, poor ventilation without visible signs of mold is also a sign that something is wrong and needs to be repaired. Unfortunately, inspecting homes with HVAC systems is often difficult without a specialized mold growth test kit available. These allow you to detect a wide variety of mold growth issues such as water damage, mildew, and more. Because of this, it is important to have an understanding of the different types of mold and how they grow.

Common indoor pollutants that can increase the risk of mold growth

While most toxic air pollutants build up in the air we breathe, sometimes carbon monoxide and other gases from the surrounding environment can build up in homes as well. These include exhaust fumes from cars and heating and cooling systems, pesticides and other agricultural chemicals, and even substances released by computers and other electronics. When these gases get too high in a room, they can mix with humidifier mist and form dangerous chemicals such as carbon monoxide. Additionally, indoor pollutants such as ammonia, formaldehyde, and benzene can also cause mildew and can be more harmful since they are hard on the nose and throat.

How ducts affect indoor air quality

HVAC Ducts collect moisture from the air, hold it in vented areas where it can evaporate, and transport it where it is needed for cooling or heating. This is where the impact of indoor air quality (IAQ) ducts on indoor air quality are concrete. Ducts can trap moisture from the air which can lead to indoor mold growth. In areas with poorly designed walls and poorly ventilated areas, moisture from the air can accumulate in the walls and form pockets of water that are thickened with mold. Areas with a humidifier also tend to have higher levels of relative humidity since water in the humidifier helps to keep relative humidity at the desired level.


Mold grows in places where conditions are right for it to grow, such as damp areas and humidifiers. The type of mold that grows in damp areas depends on a number of factors, including moisture level, seasonality, pollutants in the air, and the type of mold present in the first place. While you should always cleanse and deodorize your drains and toilets, it is important to keep in mind that certain types of mold growth can be prevented. In areas where mold is a concern, it is important to test for mold and keep track of how often you clean. This will help you identify areas of potential problem and take the necessary steps to prevent further growth. To prevent mold from growing in your home, you can either choose to maintain a hygrometer or choose the most accurate indoor air quality sensor on the market. Be sure to choose a humidifier that uses a combination of DC and gas. High moisture areas also require better air movement. The best humidifier will help to remove moisture from the air while simultaneously cleaning the air.

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