ANAHEIM, Calif. - Ninety percent of all residential duct systems have significant loss of airflow, according to recent estimates.
The losses are caused by system leaks, such as poor seals and damage to sheet metal or duct-board ductwork, or damage and restrictions found in flex-duct systems.
While the economic ramifications in terms of wasted energy are significant, the opportunities for HVAC contractors are even bigger, according to Mark Modera, who spoke at a public session during January's winter meeting of the American Society of Heating, Refrigerating and Air-Conditioning Engineers.
"Do your ducts leak?" Modera asked homeowners. "Most of what you have heard (about HVAC systems) is there's a box and there's a building. What about the ducts?"
Modera is a Ph.D. and licensed professional engineer with Carrier Aeroseal in Piedmont, Calif.
"The typical attic or crawl space duct system leaks 30 to 35 percent in the Sun Belt," he said. The energy savings potential runs from 15 percent to 35 percent, Modera estimated.
Forty percent to 60 percent of typical basement ducts leak, he continued, and there is more leakage in panned-joist returns. This results in uneven cooling and heating. Fixing the problem could save 10 percent in energy costs.
All together, Modera estimated that in the Southeast and Southwest U.S., 85 percent of the primarily flex duct or duct board ductwork leaks. In the upper Midwest and New England states, where most homes have sheet metal ductwork, 100 percent of it leaks, he said.
OpportunitiesDuct leakage and its efficiency effects are nothing new to contractors like Fred Seed, president of Arizona Air Balance Co. in Tempe, Ariz. He has been involved in air testing and balancing since 1977.
"We sometimes test for $10 (million) to $15 million homes," he said. "The gist of our work is extensive field measurements. Not many homeowners are willing to pay $500 to $600 for the report alone."
Does that mean the opportunity isn't there for residential airflow testing and balancing? No, Seed said. It just means his company doesn't target that sector, except as part of the specs for those multimillion-dollar homes - and sometimes to provide evidence in lawsuits involving tract homes.
There are similarities between commercial and residential airflow problems, he pointed out. The problems involving ductwork often result from poor installation practices.
"Duct joints are not sealed properly" primarily due to the way they're sealed, more than the product being used, Seed said. "It's more application than material."
Sealant may not be applied thick or thoroughly enough - if it's applied at all.
"This is primarily what we would see in (tract) homes," Seed said.
This agrees with findings of a study by the University of Central Florida's Solar Energy Center. In "Achieving Airtight Ducts in Manufactured Housing," the center cited these as the most common reasons for airflow losses:
- Leaky supply and return plenums
- Misaligned components
- Freehand cutting of holes in duct board and sheet metal
- Insufficient connection area at joints
- Mastic applied to dirty surfaces
- Insufficient mastic coverage
- Mastic not applied to all joints
- Loose strapping on flex-duct connections
- Incomplete tabbing of fittings
- Improperly applied tape
The study's authors recommended:
- Properly apply tapes and sealing joints with mastic
- Accurately cut holes for duct connections
- Fully bend all tabs on collar and boot connections
- Trim and tighten zip ties with a strapping tool
- Provide return air pathways from bedrooms to main living areas.
Of course, these tasks are less costly to perform before the house is completed. However, they can be done as retrofits. That's why the California Energy Commission is mandating airflow measurement and repair as one of its energy options for all residential retrofits in January 2005.
It's one thing to say, "You should seal your ducts," Modera said. "That's nice. You should also call your mother." If it's still true that California leads the country in environmental regulations, look for this one to spread, he said.
In manufactured houses, "Duct-tightness goals can be achieved with minimal added cost," the study concludes. "Reported costs range from $4 to $8 (per house). These costs include in-plant quality control procedures critical to meeting duct-tightness goals."
Checks and balancesThe main difference between commercial and residential airflow testing is when it takes place. Most testing services Seed performs in commercial and industrial projects take place before the building is handed over to the owners, at the commissioning phase. Most residential buildings are not commissioned at all - except, perhaps, for very expensive ones.
"Effective design for leakage means testing for leakage," Modera said.
In California, one study found energy savings increased 15 percent with duct system testing. Without testing - when it was assumed that people had learned what to do - there was a savings of only 4 percent, Modera said.
"You can't fix what you don't measure," he added. "Most duct systems leak."
In order for homeowners to get the efficiency their HVAC unit was designed to produce, they need to be installed by better-quality contractors, according to John Proctor, P.E., who also spoke at the session. Proctor is a principal with the Proctor Engineering Group in San Rafael, Calif.
"Residential and small commercial air-conditioning-rated efficiencies aren't automatic," he said.
Will all contractors be the best? No, he said. Will better-quality contractors cost more? Yes, because they need to maintain a higher profit margin and hire better-quality technicians.
Proctor pointed out that in one study of residential air-conditioning systems, 95 percent of them had problems with leakage, low airflow and refrigerant charges. After conducting 55,462 field tests, low airflow was found to be a widespread problem, he said.
"Efficiency is affected by low airflow," he added. It can reduce furnace efficiency and cause premature heat exchanger and compressor failures.
Commercial rooftop units had low airflow 63 percent of the time, he said.
"Quality assurance is really important," Proctor said. He said assurance could range from technicians' having a jobsite checklist to having someone in the office check technicians' measurements or having a third party check the measurements over the phone.
"Variable-speed equipment is capable of going down to very low airflow rates," said airflow-testing contractor Seed. "Any air-distribution problem is aggravated when the variable-speed system goes into low-airflow operation. For instance, if the home already has hot spots and cold spots, those problems are exacerbated by low-airflow problems. Other potential problems made worse include insufficient fresh-air intake and excess humidity, depending on the climate."
So, when does it make sense for a residential customer to have their leaky ducts repaired? It depends on many factors, including the customer's priorities and living conditions, said Seed.
"Residences have the worst IAQ of any building," he said, due to careless cleaning, extreme amounts of cleaning, cooking fumes, pets, smoking, and relying on open doors and windows for fresh air.
Poor airflow can directly affect comfort levels and energy efficiency, and can indirectly affect occupant health and medical bills. "Thorough testing and balancing will define duct-leakage problems, amount of fresh-air intake, control, unit capacity and IAQ, excluding mold," he said.
(Barbara Checket-Hanks is service/maintenance and trouble-shooting editor for SNIPS' sister publication, The Air Conditioning, Heating and Refrigeration News, where this article originally appeared.)