Does Proper Ductwork Affect Energy Efficiency?

Central heating and air conditioning rely on a system of ducts to distribute conditioned air throughout your home. This often neglected part of an HVAC system plays a critical role in achieving the desired efficiency. This guide will help you understand ducts, how they affect energy efficiency, what creates an effective system, and how to get more from your system.

Ductwork 101

Most people recognize the function that ducts play in transporting conditioned air throughout your home. However, they also play a critical role in bringing air back to the HVAC system to create a cycle of airflow through your house.

Most residential ducts consist of sheet metal or flex ducting. Sheet metal is typically either galvanized steel or aluminum. Flex ducting is a flexible metal wire wrapped in a flexible plastic and covered in insulation. Flex ducting is typically installed when space is an issue or there is extra exposure to unconditioned air, such as in attics and crawl spaces.

Energy Efficiency Meets the Ducts

Your home’s HVAC system depends on its ability to circulate air to achieve the rated efficiency. Beyond delivering conditioned air through different rooms of your home, ducts also help the system circulate the air and evenly distribute it around your home.

The circulating fan creates positive air pressure at the supply vents as it runs. Conversely, it creates negative air pressure at the return vents by drawing air into the system. According to Pascal’s Principle, pressure will equalize in a container, such as your house. By creating negative and positive pressures throughout your home, you draw the conditioned air that comes out as positive pressure to the areas of negative pressure. When your system is balanced properly, this helps keep your home’s temperature consistent.

Ductwork Design for Efficiency

There’s a science to how ducts work, and it’s more than simply running a few tubes to and from your HVAC system. Rather, there’s a balance between supply and return ducting, insulation, and the size and layout of your ductwork.

Supply Versus Return Ducting

Supply ducting delivers conditioned air throughout your home while return vents bring ambient air back to the system for heating or cooling. The size of your home determines how much air needs to circulate. Keep in mind that the amount of air out is directly related to the amount of air in. This doesn’t mean that you need the same number of supply and return vents. Rather, you need the same volume of air flowing in as what you have coming out.

It’s common to have fewer return vents and ducts in a home than supply vents. What you’ll notice is that the return vents may be larger than the supply vents. Systems are designed this way to allow the return ducts to draw the same amount of air that’s coming out from the supply vents, usually measured in cubic feet per minute (CFM).

Importance of Insulation

Metal is a great thermal conductor, so one of the problems with sheet metal ducts is transferring heat to and from the conditioned air as it travels through the system. This is especially true when the ducts travel through unconditioned parts of the house such as the attic or a crawl space. Cold or hot ducts can change the temperature of the air arriving at the supply vents, reducing your system’s heating and cooling efficiency. This is why insulating exposed ducts is critical to ensure that you’re achieving the highest efficiency possible.

Size and Layout Considerations

Your ducts have to be large enough to allow the air from the circulating fan to flow through. Supply ducts that are too small increase the pressure in the system, increase system strain, reduce HVAC efficiency and may cause unusual HVAC noises. Conversely, supply ducts that are too large do not build the proper pressure, reduce airflow from the vents and deliver too little conditioned air. Return vents matter just as much, with inadequately sized ducts and vents choking the system of the air it needs.

Duct design is also important for effectively and efficiently heating and cooling your home. For instance, too many vents on the same duct run can leave the farthest rooms with too little conditioned air arriving. The pressure from the circulating fan decreases over distance, so it’s also best to run ducts as directly as possible to your supply and return vents.

When Ducts Drive Up Energy Costs

Without the proper attention over the life of your HVAC system, ducts can drive up your heating and cooling costs. Ducts will wear over time and need proper maintenance at the right times to keep them working effectively.

Age and Wear

Ducts will wear as they age, especially those constructed of sheet metal. Duct joints and fastener contact points are the common places to wear. The ducts may vibrate over time, which may contribute to this wear. Further, moisture can build up on the metal and cause corrosion. Industry estimates suggest the average lifespan for metal ducts is 20 to 25 years at the high end, with some repair needed starting between 10 and 15 years.

Improper Sealing

Ducts are usually sealed during initial installation. Mastic sealant is considered the best and may last as long as your ducts. However, new leaks may develop over time due to wear. Industry experts recommend having your ducts inspected every three to five years unless you have symptoms of leaks. If your technician finds leaks, have them professionally seal them to extend your duct’s life.

Dirty Ducts

Ducts are also notorious for getting dirty, which can restrict airflow and reduce your system’s efficiency. The most common source of duct contaminants is the system’s supply vents. Dirt, toys, dander, and many other contaminants can fall into the vents, and work their way further into the ducts. This results in restricted airflow through the duct and reduced system efficiency. To counteract this, industry experts recommend having your ducts cleaned every three to five years, or more often if you have household hobbies or activities that generate a lot of dust. Further, you should include duct cleaning as the final part of major household projects that produce any kind of fine particles.

The Forgotten Part of Ducts: Air Filters

Air filters are commonly mentioned as part of HVAC maintenance because of their importance, but they reside in the return ducts. These must be changed regularly to keep the system operating efficiently. Plan to check your filter every month, knowing that you’ll need to replace 1- or 2-inch filters every 30 to 90 days. Larger filters may last longer depending on the filter’s construction, your home’s air quality and how you use the system.

Advanced Ductwork: Zoning

You can significantly improve your HVAC system’s efficiency by adding zoning. Traditional systems heat or cool your whole home all the time. Zoned systems improve your system’s efficiency by focusing on just those areas that need conditioned air. These systems use a system of dampers in the ducts that open and close automatically when a thermostat signals an area of your home needs heating or cooling. Having return ducts in every zone can help prevent static pressure from building, especially if any individual room is its own zone.

Property owners around Charlotte have trusted the experts at Integrity Heating & Cooling for more than 35 years. Our team provides ductwork installation, inspection and sealing together with indoor air quality solutions and AC and heating installation, maintenance and repair.

Call Integrity Heating & Cooling today to schedule a duct inspection with one of our NATE-certified technicians.