The “bigger is better” theory doesn't apply to a central air conditioning system. In fact, when it comes to all the inefficient, misguided and downright wasteful advice out there, buying an oversized air conditioner is absolutely the worst air conditioning advice of all.

It makes sense to apply the “bigger is better” theory to Thanksgiving and other family dinners: if in doubt about whether to buy the 12-pound or 16-pound turkey or ham, choose the bigger one. After all, you don't want to run out of food.

And the theory makes equally good sense when you're debating whether to buy the pair of jeans that feels a bit too snug in places or the pair that affords you a little breathing room. Choose the larger pair. After all, you don't want to feel pinched and uncomfortable.

But bigger is not always better.

Advice that boils our blood

The “bigger is better and safer” theory, applied to air conditioners, frustrates air conditioning service companies on two fronts: If the customers are the ones who decided to have the oversized unit installed, it almost certainly cost them more money than a smaller unit would have. In fact, unscrupulous companies often steer customers to oversized air conditioners simply to pad their own pockets. Their short-term goal is to make money; they're not vested in developing a reliable enterprise whose reputation depends on happy, long-term and repeat customers.

Whether people purchased an oversized air conditioner or moved into a home with one already in place, several consequences inevitably follow suit:

• Work too quickly to cool down a home, then shut off. This frenetic pattern – turning on, staying on for only a short time and then shutting off – is called short cycling. By contrast, air conditioners that are sized properly for a home run continuously because they take their time to cool down a home, allowing the cool air to circulate fully. 
  
  
• Result in humid indoor air. Short cycling means that an air conditioning system will not run long enough to condense moisture, which is why homes with oversized air conditioners often feel humid, damp and stuffy. Ironically, these homes may feel chilly in short bursts, but they still feel "clammy."
  
  
• Undermine indoor air quality. Humid indoor air is more than uncomfortable; it can be unhealthy if it promotes the growth of mildew, mold and bacteria and can be particularly bothersome to people who suffer from asthma, allergies and upper respiratory problems. To counteract these conditions, many people lower the thermostat to make their homes cooler. But this tactic simply restarts a vicious cycle (no pun intended).
  
  
• Cost more money to run. An oversized air conditioning system uses more electricity as it repeatedly turns on and off. If you're having difficulty understanding why short cycling is inefficient compared to an air conditioning system that runs continuously, equate it to how you accelerate in your car. If you regularly floor the gas pedal, there's no doubt: you'll reach your destination faster (just as your home will cool faster with an oversized air conditioner). But if you drive like this all the time – accelerating fiercely, stopping and then speeding off again – you'll use more gas. Just keep an eye on your gas gauge for proof. Driving at a moderate, continuous speed is more energy-efficient.
  
  
• Almost always fall short of fulfilling their projected lifespan than those that are “right-sized.” This consequence, too, can be difficult for some customers to understand, especially if they assume that an oversized air conditioner will simply provide the extra assurance that their air conditioning needs will be “covered.” In fact, all that short cycling takes a huge toll on an air conditioner's components.
  
  
• Are often, but not always, rather noisy. It follows that the bigger the air conditioner, the faster it will push air through ducts and grilles. It has more power. But oftentimes, a home's grilles are not designed with an oversized unit in mind, so rattling is often heard in homes with oversized air conditioners as the air channels through.

Like buying a vehicle that you eventually decide is too large for your needs, an oversized air conditioner presents a quagmire in terms of remedies. This is why Experts In Your Home emphasizes that the process of purchasing an air conditioning system must begin correctly: A home's cooling load must be assessed accurately so that the air conditioner can be sized correctly.