"Today's best air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model." Energy.gov
When is it time to replace?
Certain telltale signs indicate it's time to consider replacing heating and cooling equipment, or improving the performance of your overall system. It may be time to call a professional contractor to help you make a change if:
Your heat pump or air conditioner is more than 10 years old.
Consider replacing it with a unit that has earned the ENERGY STAR label. Installed correctly, these high-efficiency units can save up to 20 percent on heating and cooling costs.
Your furnace or boiler is more than 15 years old.
Consider replacing with an ENERGY STAR qualified furnace, which is 15% more efficient than a conventional furnace. If you have a boiler, consider replacing with an ENERGY STAR qualified boiler that is 5% more efficient than a new, standard model.
Your equipment needs frequent repairs and your energy bills are going up.
Your cooling or heating equipment may have become less efficient.
Some rooms in your home are too hot or too cold.
Improper equipment operation, duct problems or inadequate insulation could be the cause.
No one is home for long periods of the day and you do not have a programmable thermostat.
Install a programmable thermostat or have a good contractor install one and instruct you on its use — to start saving energy and money while they're away or sleeping.
Your home has humidity problems.
Poor equipment operation, inadequate equipment, and leaky ductwork can cause the air to be too dry in the winter or too humid in the summer.
Your home has excessive dust.
Leaky ducts can pull particles and air from attics, crawl spaces and basements and distribute them throughout your house. Sealing your ducts may be a solution.
Your heating or cooling system is noisy.
You could have an undersized duct system or a problem with the indoor coil of your cooling equipment.