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Duct Sealing for Efficiency, Health, Durability and Safety
2007 National Weatherization Training Conference
Orlando, Florida
Building Performance & Comfort, Inc.
• Doug Garrett, CEM, CDSM• Assoc. of Energy Engineers, Certified
Energy Manager• ACCA Certif. Instructor, Manual J, D, S• IECC Energy Code trainer for 4 years• Several IAQ/Mold Certifications• Former contractor• Consulting, diagnosing performance
problems in homes and commercial buildings, training
How Much Does Air Weigh?
• Standard air weighs 0.075 lbs./ft3 or 1.2 ounces
• Standard Air (70° F, 50% RH, Sea Level)
• A 5 ton A/C unit moves 2,000 cfm
How Much Does Air Weigh?
5 TON A/C UNIT:
2,000 CFM X 0.075 lbs/ft3 = 150 lbs/min.
150 lbs/min x 60 min = 9,000 lbs/hr
4.5 TONS/HR
How Does Air Move?
• All natural air motion is due to a difference in pressure, air moves from points of high pressure to points of low pressure
• Another answer would be that based on the duct designs and installation I’ve seen I can’t believe that it does move as well as it does in most homes!
Leaky Supply Ducts and Panned Stud Bays/Floor Joists. Don’t worry, this is only a $2 Million dollar home!
Air Tight Ducts• Amount of Duct Leakage • Impacts of Duct Leakage on EER
and Capacity• Impacts of Duct Leakage on
Moisture and IAQ• Safety Concerns Related to Duct
Leakage
How Much Do Ducts Leak?
• Studies by utilities, cities and universities found leakage averaging 30% of rated airflow!
• U.S. Dept. of Energy research found the same leakage across the nation.
• This costs us all a fortune, as in Billions of dollars each year!
What Types of Ducts Leak?
• All ducts were found to leak about the same amount.
• Flex duct and metal ducts leak at connections.
• Duct board can leak at any unsealed seam.• All building chases used as ducts leak like
cheese cloth!
What Are the Impacts of Duct Leakage?
• Forces contractor to increase tonnage to compensate for unknown loss of capacity.
• Slashes efficiency of equipment!• Costs builders, home owners billions.• Increases peak demand for electricity.• Worst impacts when conditions outside
are worst!• Back Drafting of Combustion
Appliances!
Duct Sealing• UL-181-A for metal ducts and duct board.
• UL-181-B for flex ducts.
• Tapes and mastics are both listed and available. Much better performance than “duct tape.”
• Cloth Duct Tape is illegal!
HVAC System:
• In a 3 Month Accelerated Aging Test simulating 30 Years in the field, U.S. DOE found Failure in:• Cloth Duct Tape = 7 Days• UL-181B-FX Tape = 10 Days• UL-181 B-FX Foil Tape = 10 days• UL-181-A and B Mastic = No
Failures!!
Where and How to Seal Ducts:
• Seal the fitting to the plenum or drywall with UL181 mastic.
• Seal the inner liner to the fitting with UL 181 mastic and a tie strap.
• Seal all connections, fittings, seams, joins and the air handler with mastic.
• Never ever use a building chase as a duct!
Duct Leaks
• Seal all connections, start collars, boots etc with latex water based mastic like RCD #6
• Seal all sides of the return with sheetrock, and then paint mastic on all cracks, seams, joints, etc.
• On Up flow return platforms seal the platform from underneath or inside.
• Are you Pooky challenged?Contributed by: Tom Turner
• Last week I went on an inspection at 9:30 am and in the process managed to smear pooky (mastic) over two legs and the seat of my jeans. As I work for the City and live in Cedar Park (too far away to go homeand change), I just worked the rest of the day letting the mastic set up figuring I had ruined a pair of pants.
That evening at about eight o'clock I put thepants in a full tub of washing machine water and let them soak about 45 minutes. I then added a sample packet (one wash load) of Oxyclean and ran the pants through one wash cycle. Immediately after the wash cycle ended and drained (no rinse) I then ran the washer full of water again and added my normal detergent. The washer went through the normal wash and rinse cycles and the pants came out clean. I tried this a second time and it worked on a second pair of old pants. This may be a help to those who install on a daily basis in saving some money replacing pants and shirts.