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.
Nobody likes a surprise breakdown in the middle of any season. The air conditioner will give you a bit of notice that it needs your attention by not cooling properly, likely driving up the hydro bill. With both units, keep an eye out for leaks and an ear out for unusual noises.
Keep the HVAC system shipshape, air ducts should be clean every two to five years, As well, the cleanliness and maintenance of a humidifier or dehumidifier will keep them in top working order and improve air quality.