Do not wait until things break down. If you maintain them properly, the furnace and air conditioner have a lifespan of about 15 to 20 years. Schedule an annual appointment with a heating and cooling professional who can check that these workhorses are running efficiently and safely.
In between visits, make sure you change the furnace filter every three months. A clogged filter means that your furnace has to work harder, which increases energy usage. Plus, a clean filter means to improve air quality in your home because it catches bacteria, pet dander, and other contaminants that can be particularly harmful to those with allergies or asthma.