The Importance of Sizing a New Air Conditioner Of course, an undersized unit is also problematic because it can’t keep up on the hottest summer days.
Here are the problems associated with oversized air conditioners: You should never simply buy the biggest AC unit possible, or you could end up with an oversized system. But when it comes to air conditioners, sometimes less is more. This is certainly true of meal sizes, lottery winnings, and discounts. One ton of cooling is the rate of heat transfer needed to freeze 2,000 lbs – or one ton – of water in 24 hours. The word “tonnage” is used to describe the cooling capacity of an air conditioner. It’s the amount of heat needed to raise the temperature of one pound of water by one degree. One Btu is equivalent to the heat generated by a single birthday candle. Heating and air conditioning capacities are measured in British thermal units (Btu) per hour. You can also view our chart below with the numbers and their corresponding tonnage. Divide the number by 12 (which represents 12,000 Btu/hr, or one ton of cooling capacity) to get your AC unit’s tonnage. The possibilities on residential units range from 18 to 60. Within this string of letters and numerals, you should find an even, two-digit number. Go outside to the condensing unit and look for a data plaque mounted to the side. The easiest place to look is on the AC unit itself. Is it time to replace your AC unit? Find out the tonnage of your current system to give you a place to start while shopping for a replacement.
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Why does it take so long to cool a house when an air conditioner has been off for a while?.Why has the thermostat screen gone blank?.What is wrong with an air conditioner when the air flow out of the vents is low?.How did homes stay cool in Florida before air conditioning?.Does an old air conditioner use more electricity as it ages?.Where is the air filter for my central air conditioner and furnace? I can’t find it?.How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump?.How can I find out the age of my air conditioner or furnace?.How can I find out the size of my air conditioner?.How can I find out the SEER of my air conditioner?.To learn more about heating and air conditioning systems, see these other blog posts: To determine the date of manufacture of an International Comfort system, see our blog post How can I tell the age of an International Comfort Products (ICP) air conditioner or furnace from the serial number?To find the age of another manufacturer/brand, go to How do I determine the age of my air conditioner? Make sure you use RLA and not LRA, Locked Rotor Amperage, which is the surge of amps necessary to overcome inertia and start the system. If you divide the RLA by 6 for older units and 5 or 6 for newer units, you should get a number that approximates (not exactly) the tonnage of the system. RLA is an acronym for Rated Load Amperage, and is what the maximum amperage should be when the condenser up and running. If you are unsure whether you have found the right two numbers, you can double-check it by looking for the “RLA” rating on the data plate. And this is another one that is 3-1/2 tons. Here’s a rundown of the range you will encounter: 18 = 1.5 tons, 24 = 2 tons, 30 - 2.5 tons, 36 = 3 tons, 42 = 3.5 tons, 48 = 4 tons, and 60 = 5 tons. A ton of air conditioning equals 12,000 BTU, and 48 divided by 12 equals 4, so the data plate below indicates the system is 4 tons. It will be a number divisible by 6 or 12, and represents the nominal BTU of the system in thousands. Look for the 5th and 6th digit of the model number, or approximately that location. You can determine the size in tons of your International Comfort HVAC system by examining the model number on the data sticker at the side of the a/c condenser (outdoor unit).