Bigger is Not Always Better

A common misperception on the part of many homeowners is that a bigger air conditioner cools better. The truth is over-sized air conditioners cool worse. Comfort is reduced. Utility costs are increased. Repairs are more frequent. Equipment life is shortened. Noise increases. The price is higher. So, why do so many contractors oversize air conditioners?

1. They do not know how to do the engineering to correctly size an air conditioner and rely on “rules of thumb,”
2. They do not want to take the time to run air conditioning engineering load calculations,
3. They have not invested in the necessary engineering software,
4. They are unwilling to take the time to explain to homeowner how air conditioners operate and figure it’s easier to oversize, or
5. They oversize on purpose to cover up problems and provide a “safety margin” (e.g., duct leaks, improper airflow across the indoor coil, systems with improper refrigerant charge).

Insufficient Humidity Removal

Air conditioners dehumidify indoor air. As the indoor coil temperature drops, moisture condenses on the coil. The moisture runs off the coil and is collected in the drain pan and removed. When over-sized, air conditioners short cycle. They run for a few minutes, stop, and start again. During the first few minutes of a cycle, the coil temperature drops to the point where moisture condenses on the coil. If the cycle is prematurely halted, the moisture does not run off the coil; it evaporates, returning to the air stream.
The Result: You feel “cold and clammy.”

Inefficient Operation

It takes more energy to start an air conditioner than to keep it running. Air conditioners are least efficient at the start of a cooling cycle. Because over-sized air conditioners short cycle, the overall efficiency of your air conditioner drops.
The Result: You pay more in utilities than you should.

Greater Component Wear & Tear

Constant starting and stopping taxes your system's compressor and fan motors, reducing component life.
The Result: More repairs over time and reduced equipment life.

Increased Noise

Larger air conditioners move more air, potentially making grille openings “undersized” for the volume of air. Forced through smaller openings, the velocity of the air increases.
The Result: Increased noise levels and “blasts” of frigid air.

Increased Cost

If reduced comfort, higher utilities, more repairs, and increased noise were not enough, larger air conditioners are more expensive to buy.

The Result: You pay more than necessary.

© 2013 Service Roundtable