Q. Why is sealing the ductwork important?
A. Leaky ductwork often accounts for 10 to 30 percent of total heating and cooling costs. For an average home, leaky ducts can waste hundreds of dollars each year. While the increase in energy cost is significant, protecting health and safety is the most important reason to seal ducts. Ducts are usually located in the attic, crawl space or basement. If the return ducts leak, they draw air from these areas directly into the home. This air can be contaminated with dust, mold, mildew, excess humidity, and potential toxins such as pesticides for termite treatment, combustion gases, and radon. When supply ducts leak, they can create a lower pressure inside the house which draws in contaminates, too.
Q. How do duct leaks affect heating and cooling equipment?
A. If the duct leakage is 20% of the total air flow, the efficiency of the cooling system can drop by 50%. Heating efficiency is similarly affected. Duct leakage also lowers the heating and cooling capacity and can lessen equipment life. Many comfort complaints in homes are due to poor ductwork.

Q. How do I know if a system has duct leaks?
A. Start with a visual inspection of the system. Energy codes require that all joints in the ductwork be sealed. However, many leaks are not readily visible. To determine if you have serious leakage, a pressure test of the ducts with a special fan is required. The test involves temporarily taping over the registers, then blowing air into the ducts with the fan to determine the amount of leakage as well as the location of the leaks. The test takes about an hour. Some contractors conduct the test for a nominal fee or include it as part of a bid to seal leaky ductwork.
Q. Why is duct leakage so common?
A. Most connections are simply not sealed. There is also a problem with poor quality materials being used to seal ducts. Duct tapes do not provide a permanent seal. Their adhesive dries out. Experts recommend duct-sealing mastic. Mastic is a thick paste which can be used on all duct materials and provides a permanent seal. Mastic comes in tubs and tubes. For new construction, the cost of material and labor to seal all the joints with mastic should be about the same as for a quality job sealed with tape.

Q. What are the most important areas to seal?
A. Seal in this order:

• Disconnected Components
• All Air Handling Unit Connections and Seams 
• Plenums,  Takeoffs, and  Boots
• Joints between sections of branch ductwork
• Longitudinal seams in round metal ductwork

Q. Do building and energy codes address duct leakage?
A. Yes, all building and energy codes require the sealing of air ducts. “Duct tape” is no longer permitted as a sealant on any duct.
Q. Why use RCD Mastics?
A. Studies have shown tapes are not a permanent seal and will eventually fail. RCD Corporation® Mastics are specifically formulated to permanently seal all types of ductwork. 

Q. If the ducts are insulated, do they need to be sealed?
A. Yes. Insulation does not stop air leaks. Look for dirt streaks in duct insulation, they’re a sign that air has been leaking from the ducts.
Q. Are certain types of ducts more airtight?
A. Studies show that all types of ductwork can have problems with air leakage. Mastic works to seal metal, flexible, and fibrous ductwork. Try to avoid using framing (such as panned returns) for ductwork. These create areas that are hard to seal.

Q. Where is the best location for ductwork?
A. The problems due to leaky ducts can be reduced or eliminated by bringing the ducts inside the conditioned space. If that is not possible, the crawlspace or basement is usually preferred over the attic due to summertime heat buildup in the attic. Exterior walls are bad locations for ducts because they displace wall insulation, which can lead to moisture problems.