Go poke around inside your furnace and you’ll likely find a folded sheet (like an accordion) or a fibrous mesh. That’s the filter and it’s typically located just before the cooling coil and heat exchanger.

Why does your air system need a filter?
The filter protects the furnace itself. Dust from your home gets drawn into the unit through the return ductwork. Without a filter, this dust would build up on the fan, heat exchanger and coil, reducing efficiency and eventually causing failure.

An overview of residential HVAC filters
Residential filters are either flat (made from fiberglass) or pleated (made from various materials). Filter efficiency is indicated by its Minimum Efficiency Reporting Value (MERV). The larger the MERV, the more particles it can capture.

More efficient filters have larger pressure drops as the air flows through. This makes the fan work harder, lowering system efficiency. You need to balance your furnace fan capabilities and energy use with the level of protection you want from your filter.

There are many levels of residential filters – from the most basic with a MERV 4 to HEPA (High Efficiency Particulate Arrestance) filters capable of capturing microscopic particles. For typical households, MERV 8 gives the right balance between efficiency and air cleanliness. If a family member has respiratory problems, you may have to go to a higher MERV value for your furnace.

Reasons to keep it clean
Freer airflow: Dirty filters prevent the air from flowing through them. This reduces the amount of heating and cooling your furnace can do. One major issue is that you can freeze your evaporator coil if the airflow across it is too low, eventually causing your AC unit to fail.

Efficiency: Because your fan has to work harder to pull the air through a dirty coil, the system efficiency drops off as the unit consumes more electricity. A clean filter that allows airflow will keep your consumption down.

Cleaner air overall: If the filter is choked up with dust and the air isn’t flowing freely, dust can settle in other parts of your ductwork and your home, providing breeding grounds for mold, dust mites, bacteria and allergens.

How to do it
Most furnace filters are disposable. The replacement frequency depends on multiple factors. Smokers, pet owners and people with allergies will need to replace it more often. The thickness and type also have an impact. Thicker filters need to be replaced more often, and fiberglass filters must be changed sooner than pleated filters.

If you’re concerned about the state of your filter, give us a call and we’ll make sure you (and your furnace) breathe easier.