Ductwork

Ductwork leaks in a forced-air heating and cooling systems are the biggest energy waste in a building. Such leaks can account for 10 to 30 percent of total heating and cooling costs. If the duct leakage is 20% of the total air flow, the efficiency of the cooling system can drop by 50%.

Duct leakage can also be a health hazard. 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, excess humidity, and potential toxins such as pesticides for termites. Many comfort complaints in homes are due to poor ductwork.

Start with a visual inspection of the system and pressure test of the ducts with a special fan. Do not use duct tape, since the adhesive will deteriorate after time. Use sealing Mastic to get a strong and durable bond. Some prefer the paste, while others use tape. The paste takes a little more experience.

Some older homes still use panned returns for ductwork, but it makes ductwork hard to seal.

When planning your ductwork, bring the ducts inside the conditioned space. If that is not possible, the crawlspace or basement is usually preferred over the attic due to the summertime heat buildup in the attic.
Exterior walls are bad locations for ducts because they displace wall insulation and can cause condensation problems.

Most important areas to seal:
Ductwork Ductwork leaks in a forced-air heating and cooling systems are the biggest energy waste in a building. Such leaks can account for 10 to 30 percent of total heating and cooling costs. If the duct leakage is 20% of the total air flow, the efficiency of the cooling system can drop by 50%. Duct leakage can also be a health hazard. 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, excess humidity, and potential toxins such as pesticides for termites. Many comfort complaints in homes are due to poor ductwork. Start with a visual inspection of the system and pressure test of the ducts with a special fan. Do not use duct tape, since the adhesive will deteriorate after time. Use sealing Mastic to get a strong and durable bond. Some prefer the paste, while others use tape. The paste takes a little more experience. Some older homes still use panned returns for ductwork, but it makes ductwork hard to seal. When planning your ductwork, bring the ducts inside the conditioned space. If that is not possible, the crawlspace or basement is usually preferred over the attic due to the summertime heat buildup in the attic. Exterior walls are bad locations for ducts because they displace wall insulation and can cause condensation problems. Most important areas to seal:
• Disconnected components
• Connections between air handling unit and the plenums
• All seams in the air handling unit, plenums and rectangular ductwork, especially in hard-to-reach places
• Return takeoffs, boots, and other connections, especially site-built items
• Joints between sections of branch ductwork
• Longitudinal seams in round metal ductwork

More information about duct systems or Blower-door test.