How to Clean Ducts in Your Gas Furnace

QUESTION: I have a 30-year-old home with a forced-air gas furnace. I am considering having my ductwork professionally cleaned since reading about dust mites and respiratory problems in the home. What might I expect to find in these ducts and how do these hot-air furnace duct cleaning services go about cleaning ducts? Will this cleaning kill or remove dust mites and are these services worthwhile?

ANSWER: Unfortunately, most forced-air heating systems--gas, electric or oil--are not equipped with adequate filters. Therefore, ducts in most homes have an accumulation of dust and dirt that has built up over the years. Artifacts from the occupants tend to collect in ducts: paper clips, coins, toys, potato chips, etc. Even new homes have dirty ducts--construction debris such as sawdust, nails, plaster, etc. falls into the ducts and is often left behind. These materials will be found in both the return ducts and supply ducts.

Dust mites generally live in carpets, bedding, mattress pads and clothing. These critters need a constant supply of food to exist, so they will not survive long in most duct systems. These minute creatures are just a fact-of-life for most of us and it’s difficult to completely eliminate dust mites in most homes.

You may want to consider cleaning the ducts in your home after making a thorough visual inspection. Remove the grills from the return and supply ducts and inspect using a flashlight and a mirror (to look around the bends). Access to the ducts near the furnace is usually not possible without disassembling a few duct connections. For common dust and debris, a household vacuum or shop-vac will generally be sufficient for those areas that you can reach. Excessively dirty or oily ducts that you can’t access, and the presence of molds and fungi, suggest professional cleaning.

Traditionally, professional duct cleaning services use a truck mounted industrial vacuum and bag filters. A large air duct is routed into the house from the truck and connected to the duct work near the furnace. The ducts are then “sucked clean” by the high air flow created by the industrial vacuum.

Depending upon what the dirt material consists of, blasts of high velocity air may not thoroughly clean all ductwork. There is often a thin film of oil or dust that can only be completely removed by mechanically scrubbing the ducts. Some duct cleaning services use brushes, rotating whips and other devices that are inserted into the ducts. These scrubbing tools help ensure the debris is dislodged from the duct surfaces so it can be vacuumed out.

After cleaning the ducts, some companies use foggers or sprayers to treat the interior of ducts with various chemical solutions in order to kill molds, fungi, bacteria and other biological growth in the ducts. Currently, Oxine is the only product of this type approved by the Environmental Protection Agency for treatment of ducts.

Once your ducts have been cleaned, they will begin to accumulate dust and dirt again unless you use a good filter system. Most “hardware store” filters are worthless for the very small particles that cause lung problems. Pleated filters in the 30% to 60% efficiency range are recommended for general use. Get professional help when selecting and installing these filters since they can restrict the air flow through your furnace--resulting in equipment damage and the potential for health and safety hazards.

Electronic filters are rated at 95% to 99% efficient for small particles and do not restrict the airflow. Good quality pleated filters cost around $5 to $8 and need to be replaced a couple of times a year. Electronic filters cost a few hundred dollars, are permanent, and only require periodic cleaning in the dishwasher.