How Effective Is A Furnace Filter?

Forced Air Furnaces recycle air from inside your home through Cold Air Returns (Return Air Duct Vents). This air is pulled towards the furnace by a large furnace fan where it is heated in winter or cooled in summer. It is then blown by the fan back into the rooms where it came from through floor or ceiling vents.

This 'forced' air passes through your furnace filter where many particles of dust are captured. Germs, spores, and other elements are often too small to capture.
 

Do Filters Catch All Dirt & Debris?

Filters only catch dust that make it to the furnace which is the center of your heating and cooling system. The Return Air Ducts are on one side of the furnace pulling air towards the furnace filter. The Supply Ducts are on the other side of the furnace carrying heated or cooled air throughout your house.

Furnace filters only capture light airborne particles coming through the Return Air Ducts, before they reach the furnace. The Supply Ducts do not have a filter.
 

How Does Dirt Get Into The Supply Duct Side?

If you're wondering how dirt and debris gets into the forced air vents, since this air has already passed through the furnace filter, there are two reasons

• Debris which falls into the vents.
  If you have a floor vent in the kitchen, open one up and take a look. It is often filled with food crumbs and other debris collecting all kinds of bacteria.
• Gaps in the sheet metal and flooring.
  These gaps act like vacuums when air is rushing past, pulling in dust, dirt, and debris from inside your walls, floors, and ceilings.
   

What Happens When A Filter Is Dirty?

When filters get dirty they restrict the flow of air passing through. No matter how fast your furnace fan is running, clogged filters will slow the air moving through your furnace ducts. This allows light debris to settle in the ducts where they collect and grow into dustballs. Once they become heavy, even the flow of air with a clean filter is not strong enough to pull the dust and debris into the furnace filter.

Filters on your furnace are extremely important in preventing your furnace from clogging up. However, if you forget to clean or exchange them regularly, your furnace is so powerful it will suck the filter towards the fan causing the filtering membrane to warp and deform opening up dust leaks.
 

How Has Duct Cleaning Improved?

In the 1980's, people became aware of the need for cleaner air in their homes. Companies jumped on this opportunity and designed cleaning methods that were crude and often ineffective. Despite this, the market grew rapidly. Original duct cleaning methods would loosen the dirt but were not powerful enough to suck contaminants out of the system. They used an assortment of brushes, scrapers, and what would now be considered 'low' suction vacuums. This stirred up the dirt and removed what you could see but was not effective in removing what you couldn't see. A modern and advanced duct cleaning service uses far more powerful equipment, and does a much better job.