Oversized Air Conditioning Units: Can AC Be Overdone?

You may not want to hear this, especially if you are one of those AC users who figured that more is better and installed an oversized air conditioning system. In fact, there are several undesirable issues that can arise from too large an AC unit, one of which can be damaging to your house. Whether you already have such a unit or are considering installing one, you should be aware of these points.


Drawbacks of Oversized Air Conditioning Equipment

  • Short run cycles. An AC unit too large for the needs of the space will waste energy. This is caused by too frequent and too short a run time due to the ability to put out lots of cold air at once. The startups draw lots of energy without sufficient time to thoroughly get the proper mixing of cold and warm air that is required for a smooth and balanced temperature from one part of the space to another.

  • Thermostat confusion. The thermostat is designed to sense when the cooled space has reached the optimum temperature and control it at that level. However, since the air has not mixed correctly in all areas, circulation of cold, then hot air around the thermostat sensors, can cause it to prematurely shut down the AC and then start up again very quickly after. This will result in a yo-yo effect contributing to the tendency to waste energy through additional startups and frequent short runs.

  • Noisy operation. Because the equipment is too large for the application, it will tend to overpower the ducting and the ventilation spaces and have a tendency to set up vibrations and rumbling sounds leading to louder than necessary operation.

  • Oversized inefficiency. Due to the above-mentioned incomplete and inefficient cooling, the oversized AC unit may actually not be working to cool the space as well as a more correctly sized unit would. This is a waste of initial cost, plus increased operating costs.

  • Increased repairs and maintenance costs. Because of the short run cycles, thermostat confusion and oversized inefficiency, life of the equipment will be shortened and there will be more likelihood for earlier maintenance, repairs and replacement.

  • Moisture: the most damaging effect. Unfortunately, it is not enough that the owner has inherited a wasteful, uncomfortable and inefficient situation by installing oversized equipment. The really destructive part is that cold air production requires some time for the conditions to eliminate excess moisture by condensing the moisture onto the cooling coils. Normally, enough moisture should accumulate on the coils long enough to drain off through the collection pan and the drain tube provided for this purpose. With insufficient time to condense, this moisture can remain in or evaporate back into the air and cause clammy air and a buildup in carpets, walls, clothing and other parts of the house. This provides an ideal environment for mildew and mold not only destructive to the environment of the household, but potentially a health risk.

Consult an Air Conditioning Specialist


Making sure that the system you do install is rated correctly will go a long way towards assuring you have the best economy, lowest maintenance, reliability and comfort for your money. There are several ratings, testing standards and procedures for determining the right air conditioner capacity for your needs. Contact a reputable air conditioning professional for advice on this. At the same time, he can make sure you have the right configuration of ducting, venting and airflow to match the needs of the unit. For a full evaluation, consider also asking for an air quality test.

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