There are so many choices and considerations when shopping for a new air conditioning unit. One of the more common variables is the BTU rating on the system. But what are BTU’s, does it really matter how many you have, and how do you find the right size for your home?
The BTU: British Thermal Unit
One of the few units of measure we have in common with our British counterparts is the British Thermal Unit, or BTU. This is the amount of energy required to increase one pound of water by one degree Fahrenheit.
However, in air conditioning we are concerned about cooling, not heating, so how does this apply? Whether you are heating the air inside your home or removing the heat from it, it is still a matter of heat transfer.
In this case, a single BTU would transfer the same amount of heat needed to heat the one pound of water. So if you have 36,000 BTUs, that would be the same amount of heat needed to raise 36,000 pounds of water by 1 degree.
Some units may show tonnage instead of BTUs, this is simply another measure for the BTU. One ton of cooling capacity equals 12,000 BTUs.
So the higher the BTU rating, the more raw cooling capacity the AC unit is capable of achieving. However, just because you see a high BTU capacity, does not mean it will actually provide that amount of cooling.
More Power Is Not Always Better
Your AC unit should fit both your home and your HVAC system like a glove. Too big or too small and your system will give you problems.
Smaller units will run constantly trying to achieve your desired temperature. This extra run time increases both your utility costs and the wear on your system.
However, an oversized system is just as problematic. First, larger systems require a larger amount of energy to run in the first place, raising your costs.
Next, your system will cool too quickly, reducing your cycle length. While this seems like it will reduce your energy consumption, it actually does the opposite. It runs more of these shorter cycles, increasing your overall energy consumption and wear due to frequent starts and stops.
Shorter cycles also mean your system is not providing the dehumidification that helps make your home comfortable. This means you end up paying more for a system that provides you less comfort when it runs.
Finding the Right Amount
The right size air conditioner helps to ensure your home is comfortable and your unit will last the full service life. There is a simple way to ensure you have the right size for your home.
Start by calculating your unit’s serviceable area in square feet. Keep in mind this may be different than your livable area for real estate purposes. Be sure to check your garage, attic, and basement to see if they have vents from your ducts, and include them if they do.
Next, multiply that area by 20 BTUs per square foot. So if your home is 2,300 square feet, you will need 46,000 BTUs as a starting point. This initial estimate is based on standard 8-foot ceilings and two occupants for the space.
Now other variables adjust how much you actually need. If you have more than two occupants for your home, increase your estimate by 600 BTUs for each additional person.
Also, consider how much shade your home receives. If it is shaded most of the day, you can subtract about 10% of the estimate. If it is in direct sunlight most of the day, plan to increase it by about 10%.
An experienced AC consultant will consider other more nuanced variables. This may include ceiling height, how many windows you have and their coatings, and how much of your serviceable space is subterranean or partially subterranean.
Why BTUs and Humidity Matter
As the warmer air moves across the cold evaporator coil, it condenses some moisture from the air. When the humidity rises, your system will not provide as much reduction, leaving your home a little muggier.
The more cooling capacity your system has, the more moisture it will be able to pull out of the air due to a colder coil. This is another good reason to ensure your air conditioner is the right size is to get the most humidity relief.
People around West Deptford have enjoyed the superior customer service and expertise Campbell Comfort Systems has offered since 1993. Our customers turn to us for heating and cooling installation, repair, and maintenance as well as indoor air quality solutions. Call to schedule your new air conditioner consultation with one of our expert technicians today.