Ducts and Vents

picture of vent Duct tape is good for fixing everything, including sealing ducts, right? No.

Late in 1998, scientists at the Lawrence Berkeley National Laboratory made a startling discovery -- ever-popular duct tape was useful for hundreds and hundreds of tasks, but holding ducts together wasn't one of them.

Over three months, researchers tested duct tape and 31 other sealants under accelerated laboratory conditions that mimicked long-term use in the home. They heated air to nearly 170 degrees and chilled it to below 55 degrees before blasting it through ducts. They baked ductwork at temperatures up to 187 degrees to simulate the oven-like conditions of a closed attic under a hot summer sun.

Of all the things they tested, only duct tape failed -- and they reported it failed reliably and often quite catastrophically.

Instead of using duct tape, the researchers recommended sealing ducts with mastics, gooey sealants that are painted on and allowed to harden. Metal ducts should be held together with sheet metal screws; flexible duct connections should be secured with metal or plastic bands.


Ducts in Today's Homes

Homes with central heating and air-conditioning systems rely on ductwork to distribute warmed or cooled air throughout the house.

Today's ductwork consists of insulated flexible tubes that snake across the attic floor or under the house. Unfortunately, heating ducts are out of sight and therefore out of mind. Homeowners wouldn't put up with leaking water pipes. But ductwork -- carrying air instead of water -- can leak for years, without anyone knowing it.

picture of duct Ducts can leak for reasons as simple as a protruding nail in the attic that snags and tears the duct when it's being installed. Then, too, joints and junctions where two pieces of duct come together may separate over time -- especially if that pesky duct tape we talked about was used to join them.

Contractors even forget to attach ductwork together or to connect it to the vent in the wall. As a result, an open duct wastefully pumps conditioned air into the attic or under the house, while the room it is supposed to serve never gets comfortable.

Problems also occur when ducts are blocked or kinked. Just as a pinched garden hose cuts down the flow of water, a kinked duct drastically reduces the flow of air. Kinking can happen when ducts are forced into tight places under the floor or in the attic. Make sure ducts are properly supported, don't sag, twist or bend unnecessarily, and they have no gaps or breaks.

Design is important as well. Improperly designed systems may have ducts that are too small for the amount of air they are supposed to carry, or a duct that is too large in one room may siphon off conditioned air that should be going to another part of the house. The air conditioner or heater may be either undersized or too large for the duct system, providing too little or much more pressure than the system was designed to handle.

If its duct system is poorly designed or poorly installed, a house will waste energy, no matter how well insulated it may be, or how efficient its furnace and air conditioner are. That's why it's a good idea to have your duct system examined for leaks, blockages, and just poor design. Air conditioning companies familiar with duct testing can perform the examination, and your local utility may give you a sizable rebate when you have it done. You may be amazed at the monetary savings and the dramatic increase in comfort.


Today's Improved Duct Systems

Across the country, heating and air conditioning accounts for a whopping 44 percent of the energy used in U. S. homes. Thanks to our milder climate, Californians use on average only 30 percent of their energy to heat and cool their homes; but even at that figure, consumers can cut their utility bills considerably by preventing waste. When it comes to the quality of home duct systems, the opportunities for improvement are substantial, and the rewards -- in both comfort and reduced energy bills -- can be great.

Heating and cooling systems have markedly improved in efficiency over the past two decades, in part because of California's increasingly strict building and appliance standards. New products were developed that use less energy. Forced-air heaters offer a perfect example: 20 years ago, natural gas models were 60 percent to 70 percent efficient. Because of energy requirements in the standards, today's designs are as much as 97 percent efficient, producing more heat for much less money.

California's Energy Efficiency Building Regulations now require ductwork to be insulated, just like walls, ceilings and floors. Minimum requirements call for R-4.2 insulation around ducts located in attics and crawl spaces, but the Energy Commission suggests that insulating to a factor of R-8 or higher to significantly increase comfort and energy savings.

Since the California Energy Commission introduced the first Energy Efficiency Building Regulations back in 1977, home construction techniques have also evolved. Today's homes are better insulated, with improved weatherstripping to keep heat inside during the winter. Windows have become increasingly more sophisticated, with high-tech coatings and gases between multiple panes of glass that improve their insulating value. As a result, energy savings can be startling -- providing your duct system isn't squandering the benefits.


It's Your Money

  • By sealing duct leaks, a homeowner can save an average of 10 percent of the energy required to heat and cool a new California house, according to field research by the California Energy Commission.
  • Regularly clean your air filters, supply vents and return grills. Dust and dirt cause your heating equipment to work harder. That means higher energy bills.

There is no doubt that properly working heating and cooling ducts are an important factor in a home's energy efficiency. That's why the 's residential energy efficiency building codes were revised in 1999 to reflect the importance of duct systems. The California Energy Commission now gives energy efficiency credits to California builders who properly design, install, seal and test duct systems.

These energy credits provide builders with added flexibility in design, giving them more of a selection of what energy efficiency features they can provide in new homes. Studies by the building industry show that improving duct systems can be a less expensive way to comply with energy efficiency building standards than some other options that have been available.

The new code revisions were supported by the building industry as a way to improve construction practices, and to help safeguard against potential construction defect litigation.