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In a Tampa Bay outage in August, one cool bedroom matters more than anything else the generator runs. A ductless mini-split is the easiest way to get it, because of how its compressor works.
Why a variable-speed compressor helps
ENERGY STAR explains the difference: in a conventional air conditioner, the compressor works like an on/off switch, running at full power until the room is cool and then shutting off. A variable-speed compressor, the kind in mini-splits and inverter window units, changes its motor speed to match the load.
For backup power that matters twice. The unit spends most of its time well below its maximum draw, and it doesn’t slam a full-power compressor on every few minutes, which is what makes a generator’s starting-watts rating the limit with conventional ACs.
What a 12,000-BTU unit draws
From the manufacturers’ published figures:
| Unit | Power |
|---|---|
| Pioneer Diamante Pro 12k mini-split | 1,050 W rated cooling input at full load |
| Senville LETO 12k mini-split | 230 to 800 W cooling input range |
| LG Dual Inverter window unit, 12k | 1,020 W, 9.1 A rated cooling |
| Central AC, 3 ton, for comparison | 3,000 to 3,500 W running, 5,000 to 6,000 W to start |
The rated figures are the draw at full output. A variable-speed unit only runs there while it pulls a hot room down; once the room is at temperature it throttles back, and Senville’s published range shows how far: 230 W at the bottom. What your unit draws on a given night depends on the room, the insulation, the setpoint and how hot it is outside, and no efficiency rating tells you that. A SEER2 number is a seasonal efficiency score, not a wattage.
So plan with a range: size the generator for the rated input, and expect less most of the time. For a plug-in window unit, a plug-in watt meter shows the real draw in your room.
Mini-split, 115 V
Senville LETO 12k
Senville SENL-12CD-16
A 115 V heat pump whose cooling input runs from 230 to 800 W, which makes it one of the lightest cooling loads a generator or battery can carry.
- Capacity
- 12,000 BTU
- SEER2 / EER2
- 21.2 / 10.1
- Cooling input
- 230–800 W
- Power
- 115 V, MCA 19 A
- Refrigerant
- R-454B
- Lines
- 16 ft
Suits: A bedroom you want to keep cool through an outage on a mid-size generator.
Weigh: Senville says it must be installed and commissioned by a professional. Its pages and the Amazon listing give different warranty terms; confirm before buying.
On a generator
The power is easy: a 12,000-BTU mini-split fits inside the 5,000-to-7,500-watt tier in our sizing guide with the refrigerator, fans and the internet.
The connection is the part to plan. A mini-split is hardwired to its own circuit, with no plug. To run it from a generator, an electrician installs an inlet and listed transfer equipment for that circuit. A 115 V mini-split can be backed up from a 120 V generator through a transfer switch made for 120 V circuits; a 230 V mini-split, or feeding the whole panel through an interlock, takes a generator with a 120/240 V outlet (L14-30R or 14-50R). The electrician matches the equipment to the generator and the unit.
An inverter window unit is simpler: it plugs into the generator with a heavy extension cord, with nothing installed.
Large dual-fuel inverter
WEN DF680iX
WEN DF680iX
An inverter big enough for the essentials plus a bedroom AC or mini-split, with a 30-amp 240 V outlet for a transfer switch.
- Running / surge
- 5,100 / 6,800 W gas
- On propane
- 4,500 / 6,000 W
- Run time
- 6.1 h gas, 9 h propane at ½ load
- Outlets
- L14-30R, TT-30R, 2× 5-20R
- Weight
- 94.8 lb
- CO shutoff
- CO Watchdog
Suits: The essentials plus one cool room, connected through an inlet and an interlock or transfer switch.
Weigh: Ships with a bonded neutral, which decides the kind of transfer switch the electrician fits. Run time on a 20-pound propane tank is about 9 hours at half load.
On a battery
A battery runs a mini-split for hours, and how many depends on what the unit is drawing. Using BLUETTI’s runtime formula (90% usable, 85% inverter efficiency, about 10 W for the station itself):
| Unit drawing | 2 kWh station | 4 kWh station |
|---|---|---|
| 300 W (holding a cool room at night) | about 5 hours | about 10 hours |
| 500 W | about 3 hours | about 6 hours |
| 800 W | about 2 hours | about 4 hours |
| 1,050 W (full output on a hot afternoon) | about 1½ hours | about 3 hours |
The loads are assumptions, not predictions for your room; measure yours and read across. Either way, a battery by itself is a way to cool the bedroom at bedtime or to bridge the hours between generator runs, and a full night takes a large station, a small load, or both.
A hardwired mini-split also needs the battery connected to its circuit through the maker’s home panel or a transfer switch, which is an electrician’s install. A station with 1,500 W or more of AC output can run a plug-in inverter window unit directly.
Inverter window unit
LG Dual Inverter Window AC, 12,000 BTU
LG LW1224IVSM
A 12,000-BTU window unit with a variable-speed compressor, so it slows down instead of cycling on and off. It plugs into a normal outlet and draws 1,020 W at full output.
- Capacity
- 12,000 BTU
- Efficiency
- CEER 15
- Power
- 115 V plug-in, 1,020 W, 9.1 A
- Refrigerant
- R-32
- Noise
- 44–58 dBA
- ENERGY STAR
- Certified
Suits: Renters, or anyone who wants one cool room on a generator or a large battery with no installation.
Weigh: Cooling only, no heat. It weighs 85 pounds, needs a window 27 to 39 inches wide, and carries a one-year warranty.
Still choosing a unit? See DIY mini-split kit or installed.
