How to Calculate Correct Central Air-Conditioning Unit Size Calculating the proper size for a central AC unit requires determining how much energy is required to pull heat out of the air. The calculation determines the BTUs (British Thermal Units), which can be easily converted to tonnage. Most central AC units are ranked by the tonnage of the units, such as 2.5 or 4.0 tons. The easiest method of determining the proper tonnage for your living area is to calculate the square footage of individual rooms and converting that to BTUs and tonnage. Measure each room individually for length and width including any hallways or storage areas that will be impacted by the central AC unit. Do not include rooms that are not connected or will not be impacted by the unit, such as closets, basements or attics. Multiply the length of each room by the width to determine the square footage. Convert the square footage of each room to BTUs. 100 to 150 square feet equals 5,000 BTUs. 150 to 250 square feet equals 6,000 BTUs.

250 to 350 square feet converts to 7,000 BTUs. Add 4,000 BTUs to kitchens and 1,000 BTUs to laundry rooms or bathrooms. Add each room's BTU calculation together to determine the whole house BTUs.room heater/air conditioner units Divide the whole house BTUs by 12,000 to determine the tonnage. table top ac unitRound the tonnage up to the nearest 5/10ths. protection for ac unitFor example, 4.1 tons should be rounded to 4.5 tons. 3.8 tons should be rounded to 4 tons. Alpine Home Air: Selecting Air Conditioner Size Here is how you can calculate the size air conditioner unit you will need. Does this Spark an idea? Determining a central air unit size helps you save money on energy while ensuring you have the capacity that is needed to...

Calculate the size of your home in square feet. How to Size Central Air Conditioning Units. An air conditioner's size is... Sizing an AC unit refers to choosing a unit with the correct cooling capacity for the space to be cooled. If your air conditioning unit ... Frost developing on your central air conditioning unit may seem impossible when the unit is sitting... The proper size air conditioner impacts the life of the unit, ... Buying A Central Air Conditioning System; What Size Central Air Conditioning Unit Is Needed? How to Calculate Air Conditioner Size for a House; Comments You May Also Like.... How to Determine Central AC Size How to Determine the Right Size Central Air Conditioning System How to Size AC Units by Square Footage How to Estimate the BTU Required Per Ton of Air Conditioning What to Ask When Replacing a Central Heat and Air UnitThe circuit breaker’s job is to protect wiring in the walls of your house, not the air conditioner and not the air compressor.

As long as cross sectional area of the conductor is properly matched to the circuit breaker or fuse, it’s ok. That said, if you want to protect your air compressor, you should install a motor starter protection device calibrated to the nominal current, or at most 105% of the nominal current. This device may be installed either instead of the circuit breaker, or downstream from it. A three phase motor protection device, such as Eaton’s PKZM-0 series device may be wired in a special manner for use in a single phase circuit.To meet code you should run the wire to the compressor that can handle 30 amps. Off the top of my head, I think this would be 10 gauge copper. Depending on the length of the wire run, it might be cheaper to just change out the breaker with a 20 amp. If it is a short run and the wire is just going to be in the air from the box to the compressor, I would feel safe running #12 wire without changing the breaker since the compressor is never going to be pulling anywhere near 15 amps except when starting.

There is a very slight chance the compressor could fail in a way that put 29 amps on the wiring constantly. This would overheat the wire and maybe cause a fire, but this is so unlikely a situation that it would truly be a freak accident like in one of the Final Destination movies.The other possibility of using 12 gauge wire with a 30 amp breaker would be if someone in the future removed the compressor and put in something that did draw near 30 amps continuously like a welder. They could see the breaker was 30 amps and assume the wiring could handle this. A good electrician would catch this because he would check the wire size when he installed a new load.I’m assuming you are planning on hard wiring the compressor, not use something like an oven or dryer receptacle rated for 30 amps. In that case I would always run the proper wire size. I just looked the proper wire size up and my memory was correct.Written The answers below are somewhat valid. Assuming the wiring from the panel to the point the compressor receives its supply, is #10 it is could be OK.

Codes permit Electric motor loads to have a much higher breaker or fuse rating than the nameplate running current amps. Overload protection is provided by the motor running over current protection that is either inside the motor or in a motor control associated with it.The NEC permits inverse time breakers, that you likely have, to be sized as much as 250% over the motor’s nameplate full load current. So if your Compressor Motor has a nameplate full load current of no less than 12 amps, it is ok. That current would mean a minimum compressor motor rating of 2HP. However if not, you will need a smaller breaker, or a breaker located at the point the 30 amp circuit ends and connects to the compressor. It is easier to replace the 30 amp breaker with a 15 or 20 amp rated breaker that is made for the panel, same brand or otherwise listed on the breaker’s package as fitting in that particular panel.Code wise, you cannot put anything less than a 30 amp rated receptacle on the 30 amp branch circuit, or even put a 30 amp plug on the factory provided compressor’s cord.