If usage is 20 hours a day, then payback is definitely shorter. But for a 1hp conventional AC at 8 hours daily, I don't get how the electric bill would go up to around 8k/month. I use two 0.75hp units 8 hours daily and my maximum bill was 4.5k last June * P11/kwh. My recent bill was 2.9k * P9/kwh. At P11/kwh it still would only amount to just 3.4k, at 40% savings that's just 1.3k/month for me. But then my bill includes ref and other appliances. I also cook using electricity. I'll wait for my units to conk out and hope that inverter units are the norm by that time.

Quote Originally Posted by vinj View Post
Payback is quicker because the AC is used more often. You also have to consider the condition of the previous A/C. With our house before, i replaced an old .75hp window type (non inverter) with a new .75hp (non inverter) so these were both with the same spec but with the new one in use at night the electricity bill still went down considerably.