A ductless mini-split is a heat pump for one or a few rooms. In cool mode it is often more efficient than an old window unit. In heat mode it is usually cheaper than a 1,500-watt space heater for the same room — until the outdoor unit ices or the weather drops below what the unit can handle well.
The indoor head’s fan watts are small. The outdoor compressor is the real draw, and it modulates. Nameplate “max” is not the all-day average. Hours with the setpoint far from outdoor temperature are what pile up.
Leaving a head on 24/7 at a moderate setpoint can beat blasting it for an hour after the room has gone stale and hot. It can also waste money in an empty room. The card is for the habit you actually have.
Set a typical running wattage (often several hundred to about 1,200 watts for a room-size head) and the hours. Fine-tune if you have a kill-a-watt or a label.
At 18.8¢ per kWh, 800 watts for 10 hours is 8 kWh — about 1.50 that day. That is one head. Two heads are two cards or a doubled habit, not a free extra room.
Heads
Each indoor head is a habit. Two rooms on all day is not one card at the same hours unless you mean that.
Related
Usage estimate only — not a utility bill, load calc, or advice.