Does a U-shaped inverter window AC make a power station’s job easier?
Power basics Updated 2026-08-03
On running watts, yes, and by a certified margin: at 12,000 Btu/h an inverter saddle unit draws 800 W where the fixed-speed record in this library draws 1,000 W for the same cooling. On start-up current — the number that actually decides most of these verdicts — nobody knows, because no maker of an inverter room air conditioner publishes one.
That second half matters more than the saving. 7 of the 12 published US machines here refuse a fixed-speed window unit at the start-up gate, with its running load sitting well inside their continuous rating. Swap the compressor for an inverter one and the figure those refusals were computed from does not exist in any document its manufacturer publishes.
Why Europe is suddenly buying an appliance it never had
European flats have casement and tilt-and-turn windows, not the double-hung sash a US window unit hangs in — Midea’s own installation manual asks for a double-hung opening 22–36 in wide with at least 13.75 in of clear height under the raised sash. What is selling there instead is a split unit whose indoor and outdoor halves join through a flat 2.7 cm hose passing under a closed window: no hole drilled, no refrigerant line brazed on site, no installer. Electrically it is the same animal as the U-shaped window unit — an inverter-driven rotary compressor — which is why one page can answer both.
What a fixed-speed compressor costs at the instant it starts
The fixed-speed window air conditioner, running and starting
A fixed-speed rotary compressor is wired straight to the mains. Before the rotor turns it looks close to a short circuit, and what it pulls in that moment is a property of the motor rather than of the cooling it is about to do.
Cooling capacity divided by the model’s own certified efficiency rating — the federal identity for this appliance class.
See the load record →Locked-rotor amps over rated load amps, off the compressor maker’s data sheet. The record carries a 6.0–7.0× band and this is its US mains end.
Volt-amperes, not watts: the maker publishes the locked-rotor current and no power factor for that instant.
Long enough to sit inside the window any inverter surge rating is meant to cover, which is why it decides verdicts.
officialverified 2026-08-03window air conditioner · US record
Where the six-times figure is written down
One source, because the multiple is this section’s whole argument.
Copeland’s Application Engineering Bulletin AE4-1331 R9 states that locked-rotor amperage — the inrush — runs at six times or higher than rated running current and lasts on the order of 100–300 ms. It describes fixed-speed compressors, which is the point: it is the industry’s best-documented statement about the machine an inverter unit replaces, and it says nothing about the replacement.
Open the source →What the inverter changes, and by exactly how much
The inverter saddle unit record, beside the fixed-speed one
Both records derive their watts the same way, from the capacity and efficiency rating on each machine’s own federal certification, so the gap between them is an arithmetic result rather than a comparison of two brands’ marketing.
Against 1,000 W for the fixed-speed record at the same capacity: a fifth less electricity for the same cooling.
See the load record →The mid-capacity model. A 12,000 Btu/h inverter unit is cheaper to run than a 10,000 Btu/h fixed-speed one, which is the part most buyers get backwards.
Against 0.90 on the fixed-speed record. An inverter unit’s drive rectifies with power-factor correction, so the volt-amperes an inverter has to supply are almost exactly the watts — the fixed-speed unit asks for about a tenth more apparent power than its watts suggest.
See the load record →The one inverter compressor in this library whose maker publishes locked-rotor amps at all — and they come in below its own rated load amps. A drive ramps the motor up instead of connecting it to the mains.
See the load record →officialverified 2026-08-03inverter window air conditioner · US record
The saving is not a marketing round number. Input power is cooling capacity divided by the efficiency rating, so watts move as one over that rating: 15.0 against 12.0 is a ratio of 1.25, which is the same statement as a 20% cut in watts. An efficiency label converts into a wattage without anyone publishing the wattage — which is exactly why the running half of this comparison can be stated and the starting half cannot.
The number nobody publishes, and what we do instead of inventing one
Everything above describes these machines while they are running. Nothing describes one starting, and that is not a gap in our reading. The manufacturer documents behind both inverter records were searched end to end for locked rotor, LRA, inrush and starting current, and for the German equivalents. The count of matches was zero — and the US manuals do not carry a running-current table either, which the fixed-speed manual behind the other record does.
The absence, as the two records carry it
The empty state is the finding rather than a to-do, and an absence is only worth anything if it is specific about what was opened and when — so both records carry the document list and the date beside the blank.
Not a blank waiting to be filled. Three manufacturer user manuals and the federal certification dataset were searched for it on 2026-08-03; the manuals carry no electrical specification table at all, and the dataset has no such column to be empty. On the fixed-speed side the same figure exists one level down, on the compressor's own data sheet — the inverter compressor catalogues do not carry that row either.
The same finding in German, on a manual that is otherwise the most complete electrical table in this library: it publishes watts and amps for rated cooling, rated heating and the nameplate ceiling, and nothing at all for the start.
Counted from the two records’ own absence-verification blocks, which list each document URL. The date is when the absence itself was confirmed, not when some other field happened to be touched.
The maximum the maker declares the unit draws continuously, against 1,230 W at its rated cooling point. It is a floor on the machine you would need — never a start-up figure.
See the load record →officialverified 2026-08-03inverter air conditioner records · start-up fields
What the missing number would have decided
Live engine runs against the fixed-speed record on this build. Read the percentage — running load as a share of continuous output — and then read the verdict, because on two of these three rows the two disagree completely.
The one published US machine here whose surge ceiling clears this compressor’s start.
Show the working →Refused while using barely a quarter of its continuous output. Neither its battery nor its inverter rating is the problem; the instant is.
Show the working →This record can be shown to hold the load for a real number of hours, and still cannot be shown to start it. The duration gate is never reached.
Show the working →How to check your own unit
Both return the manufacturer’s declared data rather than a review site’s summary of it.
The ENERGY STAR certified room air conditioner dataset is an open endpoint carrying capacity, efficiency rating, annual kilowatt-hours, voltage, refrigerant, mounting type and whether the compressor is variable-speed, per model. It carries no start-up current for any model in it.
Open the source →Every appliance sold with an EU energy label carries a registration number in the EU’s own product database, and the record comes back as data. The cooling-only PortaSplit is registration 2517927. Note what a split-unit registration omits: rated input power in watts, and rated current. For those you still need the manual.
Open the source →