4 Signs of Bad Ductwork Installation & What to Look For

Bad ductwork installation can impact homes old and new, decreasing quality of life and decimating the efficiency of your HVAC system.

What are the signs of bad air duct installation? How can you address potential HVAC problems resulting from poor duct installation or the resulting damage? Our experts are here to help.

High energy bills, poor indoor air quality (IAQ), uneven distribution of cooled or heated air flow, and mold and mildew issues can all indicate a potential ductwork problem. But, when it comes to mitigation, you might have to call in reinforcements and consider professional attic services. 

#1 High Energy Bills

One of the most telling signs of bad ductwork is a high energy bill. 

If you’ve recently installed new ductwork or replaced your whole HVAC unit, you should expect reduced energy costs—new HVAC equipment generally promises increased energy efficiency and, thus, lower power bills. 

But, if your electric bill is still through the roof after an HVAC replacement, bad ductwork could be the culprit, causing:

  • Duct leakage, increasing the demand on your HVAC equipment to reach your desired temperature
  • Poor circulation of conditioned air—some rooms might be ice cold, while others stay warm even if the thermostat is set at a low temperature
  • Inefficient air intake at the return vents

All of these can make your HVAC system work harder to maintain your home’s temperature, increasing your energy demand and your costs. 

#2 Poor Indoor Air Quality (IAQ)

Indoor air quality (IAQ) describes the condition of the air both inside and around your home, particularly regarding your health and safety.1 

HVAC ductwork provides mechanical ventilation, replacing indoor air with outdoor air at an appropriate air exchange rate. But, if your existing ductwork is leaking or isn’t properly vented to the outside, your air exchange rate may decrease, reducing your IAQ as indoor pollutants become trapped inside. 

While you may think the primary role of an HVAC system is to condition your indoor air, it also plays a crucial role in maintaining IAQ, impacting the levels of pollutants like:

  • Excess moisture
  • Pollen or other biological pollutants
  • Pesticides
  • Fumes from household cleaning products
  • Dust

If you feel like your home would benefit from an additional air filtration device, your existing ductwork may not be up to snuff. 

#3 Air Distribution Issues

A functional HVAC system should disperse conditioned air evenly throughout your home via well-sealed ducts. 

But, a common sign of a bad duct system is uneven conditioned air distribution, which can look like:

  • “Hotspots” in specific areas of a room
  • Rooms that don’t seem to get to or stay at the desired temperature
  • Ineffective “zoning” functions promised by the manufacturer or installer

As briefly mentioned above, this issue places additional demand on your HVAC equipment, increasing your energy use and, therefore, your electricity costs. So if you notice a combination of both uneven distribution and increased costs, your ductwork might be the cause. 

#4 Mold and Mildew Odors

If your ducts are leaking or the attic vapor barrier isn’t well-sealed on the outside, condensation in the attic could build up on your ducts—especially in hot or humid climates.2 

While duct condensation might not be immediately noticeable (unless you see it happening in your attic), it can lead to moisture collection and increased humidity in your attic space, both of which can lead to mold or mildew growth. 

The following might be signs of mold or mildew issues in your attic:

  • Unpleasant odors
  • Spore growth on ceilings or walls
  • Persistent indoor humidity
  • “Thick” indoor air (or low IAQ)

If you’re experiencing mold or mildew odors in your house, it could be due to improperly installed insulation, which can lead to more negative effects. If you find yourself wondering, “can insulation make you sick,” read up on the topic to ensure you can prevent these risks with an experienced insulation installation expert.

You should take steps to eradicate mold or mildew growth as soon as you notice it—use a bleach solution when duct cleaning to kill the spores and prevent new sprouting. But you should also determine the source as an additional prevention method. So, make sure to check for leaks in your attic space and condensation on or in ducts. 

Benefits of High-Quality Ductwork Installation

When ductwork repair or installation is done right, you’ll reap benefits like:

  • Peak system efficiency, which can reduce your energy costs and your carbon footprint
  • Increased IAQ, a major element of your quality of life (especially for those with allergies)
  • Evenly and effectively cooled spaces without any hot or cold spots
  • Decreased likelihood of mold and mildew growth that can decimate your IAQ

But if you notice signs of bad ductwork installation, it’s important to take action as soon as possible. Take the following steps if you encounter a problem:

  • Contact the original installer to see if your ducts are still under warranty.
  • Contact the duct manufacturer to check for recalls or known performance issues.
  • Reach out to a qualified attic services provider in your area for further assessment and professional mitigation.

Manage your Ductwork with Attic Construction

Bad ductwork installation can wreak havoc on your energy efficiency, IAQ, and HVAC system’s operation as a whole—all of which can significantly impact your quality of life. 

If you suspect a ductwork problem, it’s time to call in reinforcements. Attic Construction has been helping California homeowners tackle their most pressing attic concerns for over a decade, and we’re committed to quality work and customer service. 

In addition to ductwork services, we offer insulation installation and removal, rodent proofing, and attic-cleaning in Orange County, San Diego, and Phoenix —the services that keep your attic functional and safe.

Contact us for professional, timely, and high-quality attic services. 



  1. US Environmental Protection Agency. Introduction to Indoor Air Quality. https://www.epa.gov/indoor-air-quality-iaq/introduction-indoor-air-quality 
  2. US Department of Energy. Minimizing Energy Losses in Ducts. https://www.energy.gov/energysaver/minimizing-energy-losses-ducts