Originally Published: November 22, 2013 6 a.m.
Question: Why do heating and cooling ducts impact energy costs so much, and why do I regularly see advertisements in the Courier for duct maintenance and cleaning services?
Houses with forced-air heating and cooling systems use conduits called ducts to distribute conditioned air throughout the home. But in many homes, up to 40 percent of the air that moves through the duct system is lost due to leaks and poorly connected registers. The result is higher utility bills, cold rooms and difficulty keeping the homes temperature stable and comfortable.
For new construction it is imperative that the HVAC contractor perform an engineering analysis following the Air Conditioning Contractors Association (ACCA) manual J, S and D computer simulations. The D simulations determine duct layout and sizing based on room heat gain/loss, air flow and static pressure.
The primary objective is to seal all the major metal trunk joints and connections with screws, tape and mastic, minimize bends and kinks in the flexible ducting and ensure all room registers and boots are sealed. Insulation integrity also is important especially in vented attics and crawl spaces. It also is imperative that installation follow a set of standard procedures like those listed at http://www.greenhomeenergyadvisors.com/articles-and-technical-information/heating-and-cooling-systems/duct-design-and-installation/
It is recommended that these specifications be attached to a new, replacement or upgraded HVAC duct system contract. It is also recommended that verification of compliance to these specifications, and testing for leakage be completed before the HVAC unit is installed or insulation applied.
A duct system that meets the ACCA standards and is properly sealed and insulated can make your home much more comfortable, highly energy efficient, and healthier.
For existing homes numerous studies conducted by nationally recognized research organizations have shown that testing and sealing leaky duct systems is one of the most cost-effective energy improvements available; if done correctly! In addition to the energy savings duct leakage repair improves homeowner comfort and reliability by allowing the HVAC system to work as designed.
Signs that your home may have a duct problem include above average summer and winter utility bills; rooms that are difficult to heat or cool; stuffy rooms that never seem to feel comfortable; and high levels of dust and pollution; and this maybe why your ducts need cleaning.
Because air leaking from ductwork is out of sight, most leaks go unnoticed by homeowners. In addition, ducts are often installed in difficult-to-reach spots like attics and crawlspaces, or are "buried" inside building cavities.
The largest impact on performance is leaks in the supply ductwork causing conditioned air to go directly outside or into a vented attic or crawlspace rather than delivered to the home. Leaks in the return ductwork suck outside air into the home reducing both efficiency and capacity. Return leaks also draw air into the building from crawlspaces, garages and attics bringing with it dust, mold spores, insulation fibers, radon and other contaminants.
Leakage also occurs within conditioned space, but the energy efficiency penalty is thought to be much less significant. Although duct leakage in homes with indirectly conditioned attics and crawlspaces steal conditioned air away from the living space. Leaky return ducts also can depressurize the water heater or furnace location and draw back carbon monoxide into the home. These problems all suggest that controlling duct leakage to the inside may be just as important as leakage to the outside.
Most homeowners choose to hire a professional contractor for duct maintenance. However, make sure the contractor you choose inspects the whole duct system, including the attic, crawlspace, garage and basement. Establish duct leakage with a duct tester and evaluate the system's supply and return air balance and static pressure before work begins. They should then repair damaged ducts, straighten out flexible ducts, seal all leaks and connections with mastic and metal tape and seal all registers and grills tightly to the ducts. They also should insulate ducts in unconditioned areas with duct insulation that carries an R-value of 6 or higher.
Finally, they should conduct a combustion safety test after the ducts are sealed, and evaluate air flow and leakage levels comparing the before and after results.
For more information contact Paul Scrivens at www.greenhomeenergyadvisors.com Blog: www.greenhomeenergyaz.com