When it’s time for a new air conditioner, you may have time to consider your options, or you may be in a pinch. Either way, finding the right size unit for your home is important to keep it comfortable. Here is what you need to know about air conditioner sizes and how to choose the right one for your home.
How Is Size Measured?
Air conditioner size refers to the maximum cooling capacity while operating at its peak. You will see this listed as BTU or tons.
BTU stands for British thermal unit, which is the amount of heat needed to raise 1 pound of water by 1 degree Fahrenheit. In terms of cooling, it refers to the amount of heat the system transfers out of the house every hour. So, a unit rated 36,000 BTU will transfer enough heat to warm 36,000 pounds of water by 1 degree every hour.
You may also see capacity in terms of tonnage, such as a 2.5-ton unit. This is simply another way of looking at BTUs, with 12,000 BTUs equaling 1 ton.
How Air Conditioning Works
To get a better understanding of BTUs, it may be helpful to know how your system works. While you feel cold air coming from your vents as your system runs, it is actually transferring heat outside. Your system works to absorb heat from the air flowing through your HVAC system and venting it outside.
This means that in order to work, it must first be able to circulate air properly. If too little air flows through the system, it cannot work effectively.
It also circulates refrigerant to absorb and vent the heat. As the refrigerant enters the evaporator coil, the pressure drops, and it becomes cold. Then, when it gets outside, the compressor increases the pressure. This raises the temperature, making it hot enough to transfer the heat as air flows through the condensing coil.
If the pressure cannot regulate properly, then it cannot complete the process. The higher the capacity rating, the more heat the refrigerant can transfer every hour.
In addition to cooling the air, your air conditioner dehumidifies the air circulating. As the air runs over the evaporator coils, it cools quickly, condensing some of the moisture it contains.
The AC Needs to Be Just the Right Size
Given that BTU is a measure of cooling capacity, it is reasonable to think that more might be better. However, you really want a system that is properly fitted for your particular situation.
If your system is too small, it will run longer cycles than intended and will struggle to reach your desired temperature. These long run cycles increase your utility costs and add unnecessary strain to your system. This not only causes components to wear more quickly but reduces the service life of your entire system.
Having a system that is too large will cause many problems as well. The best way to get the most from your system is to ensure it is the right size for your home.
The Many Problems of Too Many BTUs
A system that is oversized for your home will have just as many problems as a system that is too small. Getting a higher capacity air conditioner does not increase the airflow capacity of your HVAC system. This leaves you circulating the same air volume while making that air cooler.
Just like an overheated oven fails to cook food properly, an AC that’s too cold fails to cool properly. It does shorten the cycle length, which seems like it may save you money. However, being the air volume is constant, the house warms back up quickly due to less actual air being cooled.
This leads to more frequent cycles, meaning you have more starts and stops. These are hard on your system, causing excessive wear, especially to the compressor.
It also does not dehumidify your air as well, being it is cycling less air during the shorter cycles. Therefore, you pay more to run the larger system and more to fix it with less comfort obtained.
Air Conditioner Sizes and Costs
Two factors generally affect the cost of a new air conditioner, the brand and capacity. While higher-quality brands do cost more, the cooling capacity is more of a driver of the end cost.
The more cooling capacity a new unit offers, the higher the ticket price tends to run. So, if you choose to increase your capacity, you will pay more for the unit. This means an oversized unit costs more to install, more to run, and more to repair due to more frequent breakdowns.
The best option is to find a unit that is just the right size for your home. Here are the steps to determine the right size for your next unit.
Step 1: Calculating Your Serviceable Area
Your first step is calculating the serviceable area served by your air conditioner in square feet. A good place to start with this is the livable area in your last real estate listing. However, this may not encompass everything.
For instance, these listings may not include the garage, attic, or basement in their calculation. To see if you need to include these in your AC capacity, simply look to see if there are vents anywhere in these spaces.
Even if you close the vents in these rooms, you still need to consider them in your calculation. This is because there is still energy loss in the ducts, and air must still reach these spaces.
Step 2: Determining Base Capacity Need
After calculating your serviceable area, you need to multiply it by the needed BTUs per square foot. The general rule of thumb is using 20 BTUs per square foot. This is not a perfect calculation for every space, but it is a good starting point.
If your home has 1,600 square feet of serviceable area, you should start with a 32,000 BTU rating. Having an idea of your initial need will help your AC technician move toward the recommended unit more quickly.
Step 3: Considering Variables
There are several additional factors that affect the cooling capacity required for your home. The most important is the number of occupants in your home.
The initial calculation accounts for two occupants. For every additional person, add 600 BTUs to your need.
Then consider whether your home is shaded or in the sun most of the day. This may adjust your need by as much as 10%, either up or down.
Step 4: Final Evaluation
There are other variables to consider, including whether any of the areas are subterranean, your ceiling height, and the number of windows. An experienced HVAC professional will take all of this into account when evaluating your home and AC needs.
For over 70 years, Oak Island Heating and Air Conditioning has served people around San Marcos with expert air conditioning services. Our team provides heating and air conditioning installation, repair, and maintenance, in addition to indoor air quality solutions. Call to schedule a consultation with one of our air conditioning experts today.