Is My AC Using Too Much Electricity for the Outdoor Temperature

Check the reading against the manufacturer's expanded table at the outdoor temperature it was taken at. One Goodman 16 SEER 3-ton system, the GSX160361 with its CA*F4860 coil, draws 2.43 kW at 65°F outdoor and 3.12 kW at 115°F with the same 80°F/67°F air entering the indoor coil, 28% more on the hot day, and its outdoor unit goes from 8.9 to 12.7 amps.

The rated draw comes from a single test point. DOE defines EER at 95°F outdoors, so a meter on a 105°F afternoon or a mild spring morning should not match that number. For the rated figure itself, the free AC amps and watts calculator works out running watts and amps from a unit's capacity and EER2, and watts from a clamp reading. The next step is checking whether a reading you took is normal for that day's weather.

How much power should an AC draw at today's outdoor temperature?

Read it off the manufacturer's expanded cooling table at the outdoor temperature you measured. On the Goodman GSX160361 3-ton with the CA*F4860 coil at 1,200 CFM and 80°F/67°F return air, total system power runs 2.43, 2.61, 2.76, 2.90, 3.02 and 3.12 kW from 65°F to 115°F outdoor. Across every indoor condition and airflow in the table, each row spans 0.31 to 0.43 kW.

DOE's 2023 standards FAQ ties EER to 95°F outdoors.

DOE 2023 Central Air Conditioner Standards FAQ § What is an energy efficiency ratio (EER)?

"The EER is the ratio of the cooling capacity ... to the power input (in watts) at 95F" - U.S. Department of Energy, energy.gov

The expanded table shows what happens at every other outdoor temperature. These rows come from pages 17 and 18 of the GSX16 spec sheet, model GSX160361 with the CA*F4860 coil and TXV. The middle columns are the 80°F/67°F, 1,200 CFM cells. The bands are the lowest and highest value at that outdoor temperature across all 45 combinations of indoor dry bulb (70 to 85°F), wet bulb (59 to 71°F) and airflow (1,050 to 1,350 CFM).

Goodman labels the kW column "Total system power" and the amps column "outdoor unit amps (comp.+fan)." Use the amps column for a clamp on the condenser and the kW column for a whole-system power reading. Other brands publish the same kind of table, but check the footnote for what each column includes.

Use the table for your exact outdoor unit and coil match. The same spec sheet shows why. Goodman's other 3-ton GSX16 table, pages 19 and 20, covers the GSX160371 and GSX16A361 with the same CA*F4860 coil. At 80/67 and 1,200 CFM it also lists 2.90 kW and 11.3 A at 95°F, but 2.11 kW at 65°F and 3.60 kW and 14.5 A at 115°F. The GSX160361 match is a cased coil on a furnace, so a whole-system reading also carries the furnace blower's actual draw, which can differ from what the kW column assumes. The outdoor amps column is the cleaner comparison.

How much do indoor air and airflow change the draw?

In the GSX160361 table, much less than the weather. At 95°F outdoor, 80°F dry bulb and 1,200 CFM, raising entering wet bulb from 59°F to 71°F moves total power from 2.76 to 2.99 kW, and airflow from 1,050 to 1,350 CFM moves it from 2.83 to 2.92 kW. Going from 65°F to 115°F outdoor at fixed indoor conditions moves it 0.69 kW, three times the humidity effect.

Here's the 95°F row at 1,200 CFM and 80°F dry bulb, read across the wet bulb columns, plus the airflow and dry bulb effects at 67°F wet bulb:

So a humid house on a hot afternoon sits at the top of its row, and a dry evening sits lower. Neither explains a reading far outside the band.

How do you check a meter or clamp reading against the table?

Take the reading in steady cooling, note the outdoor air entering the condenser, the air entering the indoor coil and the supply voltage, and find the row. On the GSX160361 at 100°F outdoor, interpolating gives about 11.65 A on the outdoor unit at 80/67 and a band of 10.5 to 12.3 A. A 12.1 A reading is inside it. 13.8 A is 18% over the 80/67 value if the table is at 230 V.

The steps, on any brand with an expanded table:

1. Get the model and coil numbers and the expanded cooling data for that match.
2. Let the system run in steady cooling, then measure the air entering the condenser coil, the dry bulb and wet bulb of the air entering the indoor coil (in the return plenum, ahead of the coil), and the voltage at the disconnect.
3. For amps, clamp the outdoor unit's supply and compare with the outdoor amps column. That comparison needs no power factor, because Goodman's column is current too. Goodman doesn't print the voltage behind the column. If it is 230 V, the same power on 208 V draws about 10% more current (230 / 208 = 1.106, our estimate), which turns the 100°F value into about 12.9 A and the band top into about 13.6 A. Then the 13.8 A reading is about 7% over, close to the band.
4. For watts, use a meter that reads true power on the outdoor unit and the air handler or furnace blower, or the utility's interval data for an hour in which the AC ran the whole hour, minus the house's background load, and compare with total kW.
5. Interpolate between outdoor rows. The 100°F values above are our straight-line estimate between Goodman's 95°F and 105°F rows.

A reading inside the band says the unit draws what its maker lists for that weather. One above the top of the band is a reason to check the condenser coil and the charge by the manufacturer's procedure. The table can't tell you which.

A clamp reading times volts gives apparent power in VA. To get watts, enter the power factor on the AC amps and watts calculator if you have it. DOE's motor fact sheet defines power factor as "the fraction of power actually delivered in relation to the power that would be delivered by the same voltage and current without the phase shift."

Is 76 kWh a day normal for one AC?

For the two Goodman GSX16 3-ton matches, only with nearly nonstop runtime. The GSX160361 reaches about 70 kWh in 24 hours at 2.90 kW, its 95°F draw. At 3.27 kW, its highest cell, 76 kWh takes about 23 hours. The GSX160371 lists 3.60 kW at 115°F, about 21 hours to 76 kWh. On either, 76 kWh means nearly all-day runtime, which can't separate a weak unit from a sound one in extreme heat.

That number comes from an r/hvacadvice post from Texas: an apartment of about 1,370 sq ft, power on with almost nothing but the AC running, per the poster, 39 kWh the first day and 76 kWh the second, triple-digit outdoor temperatures, and a thermostat found at 68°F with the house in the mid 70s. The unit's labels were gone, so the two Goodman 3-ton tables are stand-ins.

1. 24 h x 2.90 kW = 69.6 kWh, and 24 h x 3.27 kW = 78.5 kWh.
2. 76 kWh needs about 23 hours even at 3.27 kW, the highest cell in the GSX160361 table, and more than 24 at 2.90 kW.
3. The GSX160371 and GSX16A361 table lists 3.60 kW at 115°F and 3.22 kW at 105°F, both at 80/67 and 1,200 CFM. 76 kWh takes about 21 hours at the first and about 23.6 at the second.
4. 39 kWh is about 12 to 13 hours at 2.90 to 3.27 kW.

Daily energy is draw times hours, so the hours are the first thing to check, and then the setpoint. Manual J designs for 75°F indoors in summer. ACCA's Ed Janowiak puts it as "75 degrees dry-bulb temperature at 50 percent relative humidity that is backed in manual J." A thermostat at 68°F in triple-digit heat sits 7°F below the indoor condition Manual J designs for, so nonstop runtime there can be normal. At a normal setpoint, a unit that runs all day without reaching it has either lost capacity or faces more load than it was sized for. Lost capacity from charge, a dirty coil or low airflow is a service check by the manufacturer's procedure. A load bigger than the unit is a Manual J question. The free whole-house Manual J calculator runs one from the ZIP code and a short description of the house.

Can one AC use 264 kWh a day?

Not the Goodman GSX160601 5-ton at anything near its listed draw. With the CA*F4961 coil and TXV it peaks at 5.11 kW anywhere in its expanded table, at 115°F outdoor, 85°F/71°F return air and 2,250 CFM. Running nonstop for 24 hours, that is about 123 kWh. 264 kWh is about 2.2 times that, and hourly readings of 12 to 15 kWh are 2.3 to 2.9 times its peak draw.

The figures come from an r/hvacadvice post whose utility flagged daily usage of up to 264, with an hourly breakdown showing "12 to 15kw hourly spikes," after a contactor and start capacitor replacement. Energy per hour and per day is kWh, so we read those as 12 to 15 kWh and 264 kWh.

The poster's own tests tie the load to the AC circuits. Raising the setpoint to 76 cut usage to 1.2 for a few hours, and with every other 240 V breaker off for 24 hours the load stayed high. The utility had also replaced the service lines the week before. Take a unit with an EER 20% lower than this one, as an illustration. It would draw about 6.4 kW at that peak, and 12 to 15 kWh an hour would still be 1.9 to 2.3 times that draw. A reading like that calls for a true-watt meter on the outdoor unit and the air handler or furnace separately, and a question to the utility about the meter after its line work.

What throws off the comparison?

Six mix-ups push a reading the wrong way. Some make a normal draw look high: a cooler outdoor row than the condenser really sees, whole-house or whole-system watts held against one unit's number, and 208 V service read against a 230 V table. Others hide a high draw: a sun-heated thermometer, or the nameplate RLA taken as the expected current. Daily kWh without the hours misleads either way.

Checking your own unit with BuildSolver

Use the AC amps and watts calculator for the rated running watts and amps from capacity and EER2, and to turn a clamp reading into watts. Then hold your reading against the manufacturer's expanded table at that day's outdoor temperature, as above. For yearly energy and cost, the SEER2 energy cost calculator works from SEER2 and hours.

Both calculators are free without signup. Take capacity from the AHRI certificate for the match, not the nominal tons. If a data sheet prints it in kW or MBH, the BTU to tons converter puts it in BTU/h before you start.

1. Find the model, coil and expanded cooling table.
2. Measure outdoor air at the condenser, dry bulb and wet bulb entering the indoor coil, the voltage, and the current or true power in steady cooling.
3. Compare with the row for that outdoor temperature and its band.
4. If daily kWh is the worry, check the setpoint against 75°F and multiply the measured draw by the hours the unit ran before suspecting the unit.

Sources

• Goodman, GSX16 Split System Air Conditioner spec sheet SS-GSX16 (3/21), product specifications page 3 and expanded cooling data pages 17 to 20 and 26: goodmanmfg.com
• U.S. Department of Energy, 2023 Central Air Conditioner Standards FAQ (issued October 5, 2022), definition of EER: energy.gov
• Ed Janowiak, ACCA HVAC Blog, Hey Ed, why do I have to use the indoor design condition 75 degrees Fahrenheit at 50% relative humidity for summer cooling: hvac-blog.acca.org
• U.S. Department of Energy, Determining Electric Motor Load and Efficiency, Electrical Glossary, power factor: energy.gov

For estimation purposes only. Measure the unit and use its manufacturer data for a specific system.