Odor, air conditioner

QUESTION: When we turn on our air conditioner, I get a strong odor of stale air that I think that it is coming from the attic, though my husband doesn’t agree. It has been happening for a year or so. Any ideas?
D.R. Gregory, Roseville, CA
ANSWER: “It sounds like you may have a problem with your heat and air duct system,” according to Vince McDonald of McDonald Plumbing, Heating and Air Conditioning in Sacramento. “The duct system transports the conditioned air into your home. The same air that comes out of the ducts (supply air), eventually flows back to the furnace or air handler and becomes the return air. This process continues over and over as long as the system is running. It is considered a closed system.
“If the ducts are in good condition, the pressures within your home are equal to the outside of the home,” he explains. “But If the ducts are not in good condition and leak, then there is going to be any number of problems.”
”What you describe is possibly a failure in your duct system. This can cause negative pressures in your home when the system is running. The stale air from the attic can now enter the house through the leaky or disconnected ducts. The average existing home in the Sacramento area has approximately 25 percent duct leakage into unconditioned space, such as attics and under the home, according to SMUD.”
“My suggestion is to have a licensed HVAC contractor at least conduct a visual inspection of your duct system,” says McDonald. “Better yet, have one perform a ‘blower door test’ with an instrument that enables the technician to accurately test and gauge your system for duct leakage. For best results, I suggest having the ducts tested again after the repairs to accurately monitor the work. Considering how much expensive conditioned air is wasted through leaky ductwork, I am sure you can appreciate that duct sealing is money well spent.”

Schedule A Technician