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McGarry and Madsen's home inspection blog for buyers of
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How many tons is my Grandaire air conditioner or heat pump?
Tuesday, April 9, 2019
You can determine the size in tons of your Grandaire HVAC system by examining the model number on the data plate at the side of the a/c condenser (outdoor unit). Look for two numbers in a cluster in the middle of the model number. They are divisible by 6 or 12, and represent the nominal BTU of the system in thousands. 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.
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. And this is another one for a 3 ton system.
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. RLA is an acronym for Rated Load Amperage, and is what the maximum amperage should be when the condenser up and running. 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. 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. It averages around five times the RLA.
To determine the date of manufacture of a Grandaire system, see our blog post How do I tell the age of a Grandaire air conditioner or furnace from the serial number? To find out the age of another brand of air conditioner or heat pump, go to How do I determine the age of my air conditioner?
To learn more about heating and air conditioning systems, see these other blog posts:
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