Is a filter necessary to run a furnace?
No, a filter is not necessary but without the filter, the air quality will be very low. First, the dirt that accumulates in the furnace may damage it, and second the dirt gets dumped in the air can cause great health issues to a person.
A furnace filled with dirt produces heat harder than usual.
For people with respiratory problems, asthma and other problems, the dirt that flows in the air can cause serious issues and aggravate their problems. People may develop allergies because of the dirt in the air. Some of the particles that filters usually catch are mold spores, dust, and pollen.
There are some disposable filters available, like fiberglass and pleated filters. The difference between them is that pleated filters will catch particles of any size while fiberglass filters only catch big particles, nothing less than 0.3 microns. In order to work at their best, filters must be changes once a month.
There are reusable filters as well. Like the washable filter and electrostatic filter. The washable filter catches small particles because of a sticky substance that needs to be sprayed on it. The electrostatic filters, as their name suggests, use electrostatic energy to catch particles in the air. All you need to do is clean them when they get to dirty.