Undersized vs. Oversized AC Units — Both Cause Overwork
When it comes to air conditioning, size matters enormously. Many homeowners assume that bigger is always better, or that a smaller unit running constantly is simply what AC does. In reality, both an undersized and an oversized system can become overworked in very different ways.
The Undersized Unit Problem
An air conditioner that’s too small for the space it’s cooling will run almost continuously trying to reach the set temperature. On hot days, it may never get there at all. The system accumulates more operating hours in a single summer than it would in a properly matched installation, wearing out components faster and driving up electricity bills.
Signs of an undersized unit include: rooms that never cool down, the AC running all day, and high humidity levels indoors.
The Oversized Unit Problem
Counterintuitively, an AC that’s too large is just as problematic. An oversized unit cools the space so quickly that it shuts off before completing a full cycle. This is called short cycling, and it’s brutal on the compressor. Without completing full cycles, the system also can’t properly dehumidify the air, leaving the home feeling cool but clammy.
Signs of an oversized unit include: rapid temperature drops followed by quick shutoffs, high indoor humidity, and uneven temperatures between rooms.
Getting the Right Size
HVAC professionals calculate the correct unit size using a Manual J load calculation, which accounts for square footage, ceiling height, insulation quality, window size and orientation, local climate, and more. Don’t rely on rules of thumb. A proper load calculation is the only way to ensure your AC is matched to your home.