Lowering your home's temperature to a comfortable level in the summer typically requires at least one to two hours for most air conditioning systems. If you have central air conditioning, it will usually take about one hour to drop around four degrees. Less efficient window air models may take longer, particularly if they do not have enough BTUs to cool the space.

Running an air conditioner to cool an overheated house is not as efficient as running one consistently throughout the day. It is much harder for a unit to cool a house effectively when it has too much warm air to circulate. Setting your thermostat at a consistent temperature and leaving it there is much more efficient.

Purchase an air conditioning unit that is rated properly for the space you are trying to cool. When in doubt, overbuy on BTUs to ensure that your unit will have more than enough cooling power. This will cut down the amount of time and the energy required to cool a space.

Resources:

PTAC sales agent.