Metal ducts also provide superior air flow, due to their smooth interior walls that reduce turbulence and air resistance. This promotes energy-efficiency of your overall HVAC system, especially if the ducts are regularly cleaned and professionally sealed.
Rigid ducts are made from galvanized steel or aluminum. They can be either rectangular or cylindrical in shape. Rigid ducts are more durable than flexible ducts and can withstand extreme temperatures.
One of the major disadvantages of flex duct is that it lacks any form of structural support. Because of its soft, bendable make-up, flex duct can easily sag or compress over time due to its own weight. This lack of structural support can lead to reduced air flow and ineffective HVAC performance.
Rigid metal ducts offer lower airflow resistance, which means less wasted energy. With more efficiency, you can reduce your power bill while saving money in the long run.
Understanding the three types of ducting – flexible, rigid, and semi-rigid – is essential when selecting the appropriate ducting for your residential HVAC system. Factors such as space requirements, system pressure, indoor air quality, energy efficiency, and maintenance should guide your decision-making process.
An HVAC system needs ductwork and one type of ductwork used is called a flex duct, which is short for flexible duct. It moves air from the HVAC system to different areas of a building. Flex ducts are made of plastic. They are known for being very adaptable and easy to install.
Though there are different types of ductwork available in the market today, Sheet metal is most recommended as this type of air duct is non-porous in nature and thus does not allow mold or bacteria to breed in the air ducts. Sheet metal ductwork also helps you prevent the potential health risks of fiberglass air ducts.
Friction is the enemy of airflow. Unlike rigid ducts, which are cut to length within a tolerance of 1 inch or less, it's easy to cut a length of flexible duct that's several feet longer than is needed to get from point A to point B. That creates slack in the duct, which reduces airflow for two reasons.
Flex ducts are more affordable, ranging from $1 to $4 per linear foot versus $7 to $13 per linear foot for metal. Since they have a simpler installation process, the cost to install or replace flexible ducts is also lower than for rigid ducts.
The longevity of HVAC flex ductwork hinges on several key factors, including material quality, installation, and maintenance. Typically, well-installed and properly maintained flex ductwork can endure for 15 to 25 years.
Steel duct systems are the easiest to clean and will not rip or tear in the process, as polyester flexible ductwork would.
The air now has to re-pressurize to regain its turbulent flow so it can continue to push its way down the duct. It requires about 24′ or two feet to do this. This is the 'Two-Foot Rule?. Ideally, you should allow at least 24′ between takeoffs and at the end of any duct run.
603.6. 1 Flexible air ducts.
Despite the higher cost, sheet metal has numerous advantages over the other types of ductwork that typically make it the best option. Sheet metal ducts are extremely durable, as the metal used to build the ducts is fairly thick. This makes sheet metal ducts less prone to damage and leaks compared to the other options.
However, the IAPMO passed a ruling stating that flexible piping should be no longer than five feet for residential properties. After review, it was extended to six feet, but it could still cause issues with a project if you can't use flexible ducts.
Duct Replacement Cost by Home Size
Larger homes require more materials and labor to replace the entire duct system. On average, the cost ranges from $2,000 to $5,000 for a small to medium-sized home. However, duct replacement can run as low as $1,400 for smaller homes and as high as $9,000 for larger homes.
Sheet metal ductwork, often considered the most energy-efficient ductwork, is a type of duct system made from durable materials like galvanized steel or aluminum. Its benefits include exceptional durability, resistance to damage from pests, and smooth surfaces that reduce air resistance, enhancing airflow efficiency.
Insulation is not a requirement on every instance that flex ducting is used, however, it is highly recommended. The purpose for insulating flex ducting is to maintain a steady, optimum temperature within the ducting.
ATCO Rubber Products is the worldwide leader in flex duct systems. With a complete line for residential and light-commercial heating, ventilation and AC applications, ATCO builds products that are built to last.
USING THE CFM/FPM CHART
Referring to the chart, a 4" pipe will convey 395 CFM at 4500 FPM.
Sheet metal, especially when insulated, is often considered the "gold standard" type of ductwork. Usually made from aluminum or galvanized steel, sheet metal ducts are available in rectangular or tubal shapes. They're sturdy and smooth, allowing for the free flow of air through them.
Gage-It Right
The thinnest acceptable sheet metal for ductwork used in a single dwelling is 28 gage or 0.013 and 0.018 inches for galvanized and aluminum, respectively. This measurement is for around duct smaller than 12 inches in diameter and a rectangular section no bigger than 8 inches.
Ducts that leak heated air into unheated spaces can add hundreds of dollars a year to your heating and cooling bills, but you can reduce that loss by sealing and insulating your ducts. Insulating ducts in unconditioned spaces is usually very cost-effective.