I'm trying to calculate the watts used from my AC unit. Below I am including my sticker label that's on the AC Unit along with a electrical data sheet I found online for my model.

So far this is where my understanding is at:

The Fan Motor is 1/6 HP from the label which would be equivalate to 124.3082 watts

The data sheet confuses me as for the "condenser fan" in the top table, it has "Watts" listed as 210 along with "Motor hp (w)" as the same as the label. What would the "Watts" for "condenser fan" row signify? In addition, the bottom table has "Condenser Coil Fan Motor" with 1.1 for "Full load amps". Would I multiply that with the average Nominal voltage? But then that would be over the 124 Watts I get from the hp convertion.

For the Compressor, I think I understand RLA is the load at regular operation while the LRA is the load at the very begging when the compressor is at idle (so I think I just care about RLA for when it's running).

So to calculate, V * I = Power ~ 240 V * 10.3 A = 2472 Watts for the Compressor. Would I use the Nominal Voltage instead for this calculation? I'm not entirely clear as to why it wouldn't be 240 volts.

AC Unit Label

Electrical Data Table (HS26-024) https://www.manualslib.com/manual/1652283/Lennox-Hs26-Series.html?page=2#manual

  • \$\begingroup\$ Power will increase with voltage but 10% V tolerance is stated without effects on rated load amps , so I would increase I_RL by 5% and V by 5% above 230V \$\endgroup\$ May 12, 2022 at 19:40
  • \$\begingroup\$ The "Motor hp (W)" line is almost certainly the mechanical output power the motor delivers, not the power it draws from the electrical supply. The Electrical input power would be the "Watts" line below that. The discrepancy between the "210W" from that line and the (1.1A x 230V) from the other label might be a result of the motor's inductive power factor... \$\endgroup\$
    – brhans
    May 12, 2022 at 20:41

1 Answer 1


Using those calculations, you would only be able to estimate the average power drawn while the compressor is running. However, that is not too useful for the following reasons.

  1. The instantaneous maximum load is far greater. When the compressor motor first starts, its peak current draw can be four times higher than average, and if the compressor restarts, the current is higher yet, because the refrigerant is hot, causing high back-pressure.
  2. The actual average power drawn is not easily found without using a watt-hour meter, because the compressor continually cycles on and off, and the duty-cycle is dependent on air temperature, insolation, heat from household appliances, and heat infiltration past building insulation.
  • \$\begingroup\$ So I don't necessarily need to be exact. Main driver for finding the average is when my solar array is producing X amount, and temp in house is Y, then send a command to my thermostat to start my AC Unit. If my math gets me a somewhat accurate number, then I can inflate it by say 5-10% or so and that would be good enough. I just wasn't sure on my math. \$\endgroup\$
    – Kayracer
    May 13, 2022 at 15:31
  • \$\begingroup\$ If it's a battery-backed solar installation, I'd just check the battery charge state, and let the AC run if charge is over a specific amount (e.g., 70%). Then, as power is used, it would shut the AC when it would deplete the battery. \$\endgroup\$ May 13, 2022 at 15:51

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