Furnace air filter considerations

In contrast to a whole house air cleaner, a furnace air filter is meant more to protect your ductwork and air conditioning system from dust particles, rather than to clean your home air. Traditionally, a furnace air filter is less sophisticated than a home air purifier, and it aims to only capture relatively large particles of dust. Though more recently there appeared more advanced models that use HEPA or electrostatic air filtration, but those models have more of a status of central unit air purifiers rather than of a furnace filter.

It is very important that while capturing the dust particles, the furnace air filter does not restrict the furnace air flow. This is why it needs regular inspection and maintenance or replacement.

There are a few different types of the furnace filters. Probably the most common one is a panel filter made of fiberglass. It is relatively cheap and just does the basic job of protecting your ductwork/furnace fan from the large dust particles. There are also washable filters that can be reused, but those may cause problems with the furnace air flow, as typically the dirt is not washed away completely and clogs the filter.

If you want somewhat better efficiency for your furnace filter, you can use a pleated filter, which is essentially a fiberglass panel filter but with an larger surface area (increased by means of pleating or folding).

If you are after smaller particles, you can use a High Efficiency Particulate Arrestant or HEPA furnace filter. Though HEPA filters are more expensive and may require special installation, they can efficiently trap even submicron particles. Note that when a filter works long enough to accumulate trapped dust particles, it becomes better at capturing even smaller particles, but at some point may become too restrictive to the furnace air flow.

A somewhat less sophisticated alternative to a HEPA air filter is an electrostatic or electronic air cleaner that uses electric fields of an electrostatic precipitator to attract dust particles.

Centralized air purification with a whole house air filter
Advantages and disadvantages of a whole house air filter compared to a portable air purifier.