Humidity in air duct insulation resulting in it corroding

Air ducts are one of the essential components of your heating, ventilation, and air conditioning (HVAC) system. They circulate the heated or cooled air throughout the building, helping keep your living space comfortable at all times of the year. 

Despite this, they rarely get the attention they deserve because they are hidden from view, making them easy to overlook. 

However, air ducts that were poorly designed or installed can cause many problems with your air distribution system. Even when the design and installation are done relatively well, a lack of proper air duct insulation can lead to a host of unexpected issues.

Insulating your ducts is never a bad idea, but it is imperative if the air ducts pass through an unconditioned part of your house. For instance, if your air ducts are located in an unconditioned attic, they must be insulated. 

Properly-insulated ducts will help you minimize energy consumption, lower your utility bills, and increase the longevity of your HVAC system. Moreover, well-insulated ducts will also make your living space more comfortable. Click here to learn more about the air duct insulation process for homes.

If your HVAC system isn’t performing as well as it used to, or if you’ve recently noticed a significant variation in the temperature of different rooms, you should consider having your air ducts checked by a professional. Proper insulation of the ducts can help eliminate many of these problems. 

Listed below are some of the problems that proper air duct insulation can fix and factors you should keep in mind when insulating the ductwork. 

Keep an Eye Out for Leakage and Energy Wastage

The leakage of conditioned air through the ducts – and changes in temperature during transit – is a significant factor that can inflate your energy bills and reduce the efficiency of your HVAC system. Click here to learn more about air leakage from ducts.

Heated and cooled air travels through the ductwork to reach different parts of your home. If the ducts pass through an unconditioned part of your house, such as the attic, the external temperature will be significantly different from the temperature inside the house. 

If the ductwork is not insulated correctly, the air passing through the ducts in the attic would automatically become hotter or colder, depending on the temperature in the attic. 

During winter, the conditioned air would lose heat when traveling through the cold attic. Conversely, during summer, the chilled air would become hotter when passing through the sweltering attic that is not cooled by the AC. 

As a result, uninsulated (or improperly insulated) ductwork could cause you to lose up to 30 percent of the energy used for heating or cooling your home. 

Air duct insulation will help ensure that the air circulating throughout your house remains at the desired temperature.

You will need to seal any holes or gaps in your ductwork before insulating it properly. As a result, duct insulation also saves energy by preventing the leakage of conditioned air.  

If in doubt, you can quickly determine whether or not your ductwork requires additional insulation by placing your hand close to the supply register. If the air feels lukewarm – and is not at the temperature that you would expect it to be – then you can be sure that your ducts need insulating. 

Click here for more fool-proof ways to check for air duct leakage. 

Uninsulated ducts could put a significant amount of extra load on your HVAC system. 

For instance, cooling a 3,500-square-foot house with insufficiently insulated ducts could put up to half a ton of extra cooling load on your air conditioner, depending on where you live.

Naturally, this would cause the AC to work overtime, reducing its lifespan and increasing your energy bills, with no improvement in comfort. 

Moisture Buildup Could Cause Mold and Mildew Growth

Condensation – and the resultant growth of mold and mildew in your ductwork – is one of the significant problems you will have to deal with if your ducts are not adequately insulated. 

During summer, your unconditioned attic will inevitably become very hot. When the cool, conditioned air passes through the ducts in the attic, the external heat will cause condensation to appear on the ductwork. 

Over time, such condensation will lead to moisture buildup in the ducts. The moisture buildup will, in turn, lead to the growth of mold and mildew. 

Humidity in air duct insulation resulting in it corroding

The presence of mold and mildew in the ducts could result in many problems.

To begin with, it will fill your living space with unpleasant odors. Secondly, if you (or one of your family members) are prone to allergies, mold growth in the ducts could lead to severe reactions. 

If you’ve been noticing any of these problems or a general decline in your indoor air quality, you should arrange for an HVAC inspection to pinpoint the issue. 

High-quality duct insulation can effectively prevent the appearance of condensation and the resultant buildup of moisture in your ductwork.  

Insufficient Thermal Resistance (R-Value) Might Make for an Uncomfortable Home

You must stay on the lookout for this problem, even when you’re having your ducts insulated. 

The R-value of a material – also known as its thermal resistance – simply measures its resistance to conductive heat flow. In other words, the higher the R-value of your insulated ducts, the more effectively they will be able to keep the conditioned air at the desired temperature. 

Duct insulation can be of various types, and its thermal resistance can vary depending on the thickness, density, and quality of the insulating material. Usually, the thicker the layer of insulation is, the higher its R-value will be, making for more effective insulation. 

Different states require different levels of duct insulation. For instance, Alabama and Mississippi require R-4.2 and R-6 insulation for ducts, respectively.

In Georgia, the current state code requires a minimum of R-8 duct insulation if the ducts are located in an unconditioned attic. In addition, the thermal resistance must be at least R-6 if the ducts pass through any other type of unconditioned space in the house. 

The temperature difference across the different surfaces of a house can be quite significant, depending on your location and the time of year. For instance, on an Atlanta summer day, the temperature in an unconditioned attic might be as high as 120°F, while the conditioned air inside the ducts would be about 58°F.

Therefore, if your ducts pass through an unconditioned attic, the temperature discrepancy would be 62° F. Clearly, you would need a high R-value insulating material to offset this massive temperature difference to minimize the risk of condensation and energy loss. 

On the other hand, if your ducts only pass through the air-conditioned areas of your house, the duct insulation’s required R-value would be much lower. Choosing the wrong R-value for your air duct insulation could cause numerous problems down the line. 

Choose the Right Material for the Type of Ducts You Have

Essentially, three different types of insulating material can be used on your ducts. Bear in mind the required shape, rigidity, and thermal resistance that will help keep your HVAC system performing optimally.  

In order of popularity, the best materials for air duct insulation are:

Fiberglass Insulation

This material is most commonly used for air duct insulation in residential properties. Typically, the R-values of fiberglass insulation are between R-4 and R-11, ensuring that the material is versatile and effective for a wide range of climates.

Depending on the ducts you have, you can choose either rigid or flexible fiberglass for duct insulation. 

  • Rigid fiberglass insulation is typically used for rectangular ducts. These insulating boards are held against the ductwork with the help of various clasps and clamps. The thickness can range from 1 to 2.5 inches, with the R-value increasing by R-4 with every additional inch of thickness. 
  • On the other hand, flexible fiberglass insulation is wrapped around the ductwork with industrial-strength tape. The outer part of the fiberglass material is backed by foil, which offers an additional layer of insulation. The flexible fiberglass material comes in rolls and can easily be installed on rectangular and round air ducts. 
An end view of a piece air duct that uses fiberglass air duct insulation

Polyethylene Bubbles

The second most common material used for air duct insulation is polyethylene bubbles. If installed correctly, this material can provide insulation of up to R-6 at a relatively low price. 

Generally, polyethylene bubbles are placed between two radiant barriers. The radiant barriers look like simple foils with reflective surfaces. The easiest way to visualize this type of insulating material is to imagine an ordinary bubble wrap (the ones used for packaging) with a layer of reflective foil on each side.  

While not as effective at thermal resistance as fiberglass, polyethylene bubbles are cheap and easy to install. To make the most of this insulating material, you must leave a two-inch gap between the foil and the duct. Installation can be challenging to accomplish on your own, so it would be best to contact an experienced technician unless you’ve worked with this material before. 

Foil-Backed Self-Adhesive Foam

This type of insulation is best for irregular ductwork, as it is incredibly flexible, durable, and easy to install. Because it’s relatively thin, it can therefore be wrapped around irregular ducts quite easily. It can also be used in combination with other types of insulation to maximize temperature regulation. 

Foil-backed self-adhesive foam insulation also improves acoustics since it can effectively dampen loud noises coming from the air-conditioning ducts. In addition, it offers excellent thermal resistance and can be taped securely in place with relatively little effort. 

The closed-cell structure of the foil-backed foam prevents condensation and water-vapor transmission, which in turn minimizes mold growth and corrosion. This material comes in a flexible sheet with self-adhesive backing – perfect for insulating cylindrical and rectangular air ducts.  

The only drawback of this insulating material is foam products can be flammable and toxic. Hence, you must ensure that the foil-backed, self-adhesive foam was specially designed for duct insulation. The material will usually have a smooth surface that is aesthetically appealing and easy to clean. 

The Insulation Process

As you can see, improper (or non-existent) air duct insulation can cause a host of unnecessary problems in your living space.

Therefore, you should take the time to do some research and find out what type of insulation will be best for your ducts, depending on their shape, location, age, and other relevant factors. 

Once you’ve found a choice material, you’ll need to find and seal all the leaks in your ductwork, clean and dry the surface, carefully measure the insulating material, and install it securely on your ducts. While it might require a bit of time and money upfront, this process will help you save a lot of energy in the long term.  

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