'DuctFair' Boosts Installation Skills
Herritage had better get himself an assistant or two and spare himself in the future. The first-ever duct joining/forming/sealing round-robin seminar was a tremendous hit. Herritage put it together for the South Carolina Association of Heating and Air Conditioning Contractors (SCAHACC).
HVAC contractors, installers, servicers, and even building inspectors turned out in large numbers for the event at both locations. There were enough requests for the event to be held again next year for Herritage to at least consider it. (Some people wanted it again as early as this autumn, but the group's fall training is already planned.)
In Heat Pump Country
Here in the heart of heat pump country, contractors, their employees, and building inspectors need to know about proper ventilation and airflow through ductwork. It has tremendous impact on heat pump operation and customer comfort.Leaks in certain areas (crawlspaces or attics) "can draw in outdoor air to the airstream, reducing the amount of heat exchange available" and thus degrade system efficiency, he explained. In cold weather, leaks can also contribute to "cold blow" problems that occur when the system starts supplying heated air.
Duct leakage due to improper seals, failed seals, rips, poor joints, sags, etc., can affect all other ducted comfort systems (i.e., central air conditioning and gas, oil, or electric heating). It can also lead to moisture incursion into the building, depending on where the leak is and what type of climate the building is in.
"This program was developed after talking with equipment suppliers and wholesalers, all of whom said their biggest concern was in-warranty returns for equipment that had nothing wrong with it," said Herritage (CEM and president of Energy Auditors, Inc., Mt. Pleasant, S.C.). He asserted that when reviewing the causes of system failures where the heat pump itself wasn't at fault, the biggest problem that came out, over and over, was airflow.
Next Stop - Ductland
The DuctFair concept is elegantly simple. Set up a number of learning stations (in this case, nine) where a limited number of participants can learn about one essential aspect of flex, sheet metal, or ductboard ductwork, in a large, empty facility. (In Myrtle Beach it was an empty tobacco warehouse.) Limit the teaching time to a reasonable amount to cover that one essential aspect of duct fabrication or installation (20 minutes). At the end of 20 minutes, every group moves to the next station.That first morning in Myrtle Beach, 74 HVAC technicians attended. Approximately the same number was present for the afternoon repeat session. The building inspectors showed up more prominently at the Columbia event.
Station 1
The first station at the DuctFair was manned by Tammy Thompson and Keith Shull of Shurtape Technologies. They covered proper use of tapes to reduce duct leakage, specifically:
Station 2
At the second station, David Harrison of Knauf Insulation demonstrated how to wrap insulation on sheet metal ductwork to maintain its R-value and minimize the chance of condensation on the metal and outer foil covering. "The out-of-package R-value is higher than installed," pointed out Harrison. This is due to stretch-out and compression. Always use a duct knife to cut insulation, he said, and cut it twice, like a carpenter.For sealing, "Don't use mastics on tape," Harrison said. "The seal needs to be mastic-gauze-mastic or tape." Any time you staple, seal it with tape, he said.
Make sure you factor stretch-out compression when you select an R-value.
Station 3
Station 3 looked like it was the most fun. Dan West from RCD taught duct sealing methods using mastics, and he brought enough supplies for all the participants to take a shot at doing it themselves. While they applied mastic, then gauze, then mastic again to repair a split piece of duct, West gave them a lot of practical information.For instance, to prepare the duct surface before making a repair, make sure it's clean. "Spray it, wipe it, but do something," West said. "No way tape is gonna hold if you do nothing."
To apply mastic (RCD mastic #6), West had the technicians brush it on in a 3-inch-wide strip.
"That's what code says. Lay the mesh on there. If you can see an edge, that's not good enough."
When sealing around any round cuts, "Cut into the mesh and seal it," West said. "Or, seal it with silicone-latex sealant," which stays malleable for about six weeks and is practical for new construction work, he said.
When do you want to use fiberglass mesh? "When you want to pass the code," he said, noting the product has to hold after being underwater 24 hours.
Station 4
At the fourth station, Chris Baird from Hart and Cooley and Joey Henderson from Carrier S.C. demonstrated some flex duct do's and don'ts. Duct hanger must be at least 1-1/2 inches wide, they pointed out, with a maximum sag of 2-1/2 inches. The duct must be pulled tight so that friction loss is much lower. "Bends greatly increase friction loss," Henderson pointed out."Pull the inner core tight, as well as the outer core," he said. "Support it every five feet - some support every other joist, which is three feet. Don't bend it to go up, either; it needs to be a gradual upward slope."
Then, peel it back and roll it up on the boot. Come next year, Henderson stated, UL will require an interior bead at the fitting.
Flex duct needs UL-181 tape, which is stronger and lasts longer, he said. This is not metal-type tape, though some brands may be silver or black.
"Ductwork is like your veins," he said. "If it's not working properly, the system won't, either."
Station 5
At Station 5, "Cut, make, and move on!" was the rallying cry of Bob Place of Owens-Corning Technical Services. He offered tips on field fabrication of plenums, installation of take-offs that remain airtight, and proper support of duct board, pointing out that doing things quickly doesn't mean you cut out necessary steps.He also discussed common misconceptions about the safety of fiberglass. "It actually breaks down in your lungs like common household dust," he said. Asbestos, on the other hand, takes 200 years to break down.
"Fiberglass is still labeled as a carcinogen in the U.S., but that warning was dropped in Europe," he pointed out.
Fiberglass can get under your skin. If that's the case, shower with cold water to remove it, he said. It also can become embedded in clothing. "Don't wash your wife's underwear with your work clothes," he quipped. "She won't love you."
Station 6
The next stop featured Frank Clark of Tru Air, discussing how to properly size return grills and supply registers. "Is 20 by 20 right for a 2-ton system?" he asked.For problem jobs, he advised that technicians measure face velocity. "Eight out of every 10 problem jobs I have seen have had to do with airflow," he said. "Get into the habit of checking face velocity every 10th job."
Static pressure is another "snake in the grass," he said. "Some manufacturers have furnaces that create tremendous static pressure because there are no internal baffles."
He advised the following:
Station 7
At the seventh station, Atco's Ralph Koerber and Joe Smith of Coastline Supply demonstrated how to splice two pieces of flex. "Done right, it's a money-saver for the contractor," Koerber said.The method they demonstrated is the one required by the Air Diffusion Council, which Koerber also represented. It uses a mechanical fastener on the core and "code tape" (UL-181) on the outer layer.
The inner core requires an air seal and a mechanical seal, they said. Nonmetallic clamps are UL-181 listed. Use a tension tool to tighten it. That way, "You've got a good seal and a good mechanical lock," Koerber said.
It may be easier said than done, but give it two wraps of tape to get a good seal. When sealing with tape on the outside, don't compress the duct down tight; this would affect the R-value.
"It's about durability, not airflow," said Koerber, although airflow can be affected by durability. Check your work by doing a tug test, he said.
Station 8
Station 8 had some nifty tools, and at least one technician was overheard stating, "Oh look! We've got some nice toys!"John Moffett from Malco tools demonstrated how to cut a clean, precise hole in sheet metal duct. He used a metal hole cutter, an attachment that can go onto any type of drill, Moffett said.
"Allow the drill to do the cutting," he said. What he wound up with, time after time, was "a perfect six-inch hole." Using the drill attachment is easier and more accurate than shears, he said. Tim Duncan from ALCO Manufacturing then demonstrated how to attach a collar to the 6-inch hole.
Station 9
Station 9's Jerry Britt demonstrated how to connect plenums to air handlers so that they stay secure and tight. He also emphasized the importance of making tapered take-offs rather than straight.With most IAQ issues, "It's really common sense things," he said. For instance, check the airflow on the return and supply sides.
"I don't think any air handlers are ready to go in unconditioned spaces," Britt commented. "The air handler is the weak link [in the HVAC system's airtightness]. Try to avoid putting these in unconditioned spaces.
"I don't see a lot of duct leaks in straight runs," he continued. "It's where the connections are." Connections at the air handler are extremely critical, he said. "Look at the bottom connection; 25 to 50 percent have no insulation at the bottom of the connection." Mechanical "pop ups" can be set inside the pan, he said, raising the air handler up so the contractor can apply tape underneath.
"When there are leaks at the air handler in a 140 degree attic, that gets into the duct system," he pointed out. "It cuts down on cooling capacity." In crawlspace installations it can draw in moisture, odors, unconditioned air, and mold.
Publication date: 05/17/2004
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