All you need to do is time how long it runs on a hot day. If it runs a lot and still keeps the place cool, you're in good shape. If it runs only a few minutes at a time and spends the majority of the time turned off, your AC is oversized.
If your A/C is oversized, it will pump out cold air at a quicker rate, rapidly lowering the temperature. This may sound like a good thing, but it cuts the A/C cycle short and prevents your home from being cooled properly. If your A/C runs for less than ten minutes at a time, you might have an oversized unit.
Since an oversized AC is too powerful for your home, it will quickly cool your home then shut off, which can raise your energy bills and wear out your AC (from all the starts and stops).
Neither oversizing nor undersizing your AC unit is ideal. Both scenarios can lead to issues with efficiency, comfort, and longevity of the system. Oversizing: If your AC unit is too large for your home, it will cycle on and off frequently, leading to inefficient operation and increased energy bills.
If the unit is too big, it will cycle off before humidity is removed from the air. This means that it will cool quickly but the air is still sticky. Long term, this can cause the walls in the home to sweat. This is much the same as what happens when you have a cold glass of ice water by the pool on a hot day.
However, the truth is an oversized system will not do a better job of cooling the house or provide any extra comfort over a properly sized unit. Air conditioner size is calculated in BTU (British Thermal Units) and tons, and measures how much heat the system can remove from the home in one hour.
An air conditioner with BTUs that exceed the recommended square footage in your home may also take on more wear and tear over time because it will initiate its on/off cycle more frequently. It could also create a subpar cooling experience because your AC's compressor may turn off much sooner than it should.
Symptoms of an undersized AC unit include poor cooling, high energy bills, uneven temperatures and excess humidity.
Higher Utility Bills
A bigger unit simply gobbles more power than a smaller one. To make matters worse, your oversized air conditioner will likely never reach its promised level of energy efficiency. Just as it is cycling up to its most efficient level, the thermostat will tell it to shut off again.
Purchasing an AC that's too small for your home means the unit runs constantly and the indoor temperature is rarely cool enough. It's also possible you could experience uneven cooling throughout your home.
An aircon unit too big for the size of your room is likely to turn on and off more frequently and in effect, consume more energy in the process. On the other hand, an aircon that is too small for the size of your room never stops running as it will continuously work to reach your desired temperature level.
But when an oversized unit is in place, it cools far faster and limits the cycle, which causes muggy, damp conditions in many cases due to high humidity. This can also lead to mold formation and a musty, uncomfortable smell.
Central AC Size Based On Your Home's Square Footage
1,400-1,600 square feet: A 24,000 BTUs (2 tons) AC unit is recommended. 1,600-1,800 square feet: Look for an AC unit with 27,000 BTUs (2.25 tons) for effective cooling. 1,800-2,000 square feet: A 30,000 BTUs (2.5 tons) unit is ideal for this square footage.
As a guide, consider 5,000-BTU models for rooms 150 square feet or smaller, 8,000 BTUs for medium-size rooms (340 square feet), and 12,000 to 14,000-BTU models for rooms with square footage from 550 to 800. Having the correct power is imperative.
Air conditioners that are too big consume more energy, endure more wear and tear, and simply don't work as well or as long as an appropriately sized unit. This can cause higher utility bills, more repairs, and discomfort in your home.
Larger AC units may cool your home faster, but that means the cooling cycle will end faster and they will shut down faster – only to cycle back on again before very long. This rapid cycling creates a lot of wear and tear on the system, shortening its life and increasing the maintenance needed to keep it running.
A window or portable AC designed for a room would typically be described with BTUs, while a whole-home AC would be described by how many tons it is. If you have a 1,200-square-foot home, you'd need a two-ton unit. A 2,400-square-foot home would need a four-ton unit.
An oversized AC unit will cycle on and off too quickly, failing to properly dehumidify the air, leaving your home feeling clammy and uncomfortable. On the other hand, an air conditioning unit that is too small will struggle to cool your space effectively, running continuously and driving up energy costs.
Currently, the 50-60 dB range is as quiet as an air conditioner can get.
If your system is undersized, it may be possible to provide cooling in problem areas by adding a ductless unit to help out in “hot spots”. Or, it may be better to replace the system with one that is correctly sized.
A Higher BTU Number Doesn't Always Indicate a Better Product
On the other hand, AC units with too few BTUs will need to run constantly to reach the target temperature, which may add strain to the system. Therefore, it is crucial to choose the appropriate BTU based on the size of the space.
To estimate your AC tonnage needs, multiply the number of square feet you're cooling times 25. This equals the total number of BTUs you need to adequately cool your space. Next, divide that number by 12,000 to determine the tonnage capability you need in your new air conditioning unit.
First, if the system is too small for the space it is intended to cool, there may be inadequate cooling and an inability to maintain a comfortable temperature. This could result in overworked components due to the excessive strain on the system, leading to higher energy costs and a shortened lifespan of the unit.