Your equipment is more than 10 years old or needs frequent repairs and your energy bills are going up.
The age and condition of your heating or cooling equipment may have caused it to become less efficient. Oversized units tend to have shorter lives due to "short-cycle," or turning on and off rapidly, which inflicts excessive wear and tear on the compressor.
Your central air conditioner needs replacement.
In most cases, a central air conditioner can be replaced with a heat pump for a modest additional cost. This could allow you to eliminate or down-size your furnace.
Some of your rooms are too hot or cold.
This could also be due to inadequate air sealing, windows, or insulation.
Your home has humidity problems, excessive dust or rooms that never seem to get comfortable.
This could also be due to poorly insulated ductwork.