Your ductwork may require cleaning if you've noticed that your furnace isn't heating your home as effectively as it once did. By putting your hand in front of your vents and feeling how much air is coming out, you can determine the airflow.
Also, the majority of homeowners are aware of furnace filters, but they are unaware of how frequently to change their filters. Depending on the filter, you should generally change them every month or two. For a more precise timeline, refer to the packaging of your filter. Your furnace may not be heating the air as effectively as it should be, which is a telltale sign that you need to replace your filter. A new filter may also be necessary if your furnace seems to be working harder than it should be. This occurs as a result of the furnace having trouble passing air through a full filter.