Starved for air your furnace cannot operate efficiently or might even fail to get started. The furnace might be cycling as it can’t find enough air through a dirty air filter. If it still fails to start, and you don’t have a regular service person, the company that installed or maintained the furnace will likely have affixed a tag or label with their name and phone number. When it is on there is a loud low rumble coming from the vents on the other side of the house. Next time your furnace doesn’t answer the call, you are going to be able to observe where the problem lies, and you may either decide that it’s within your abilities and resources to repair this, or that you are in need of an expert HVAC technician to deal with the issue for you. As a consequence, such furnaces are rather inefficient, and frequently create high pollution levels. If you are in possession of a warm air furnace then you’ve got an air filter.
There are several different kinds of furnace filters readily available, every one of which operates slightly differently from the others to do the exact same function. For older homes plenty of times the air filter is situated just before the furnace. When an ac filter becomes clogged it may even result in significant damage to the unit.