How to actually size an air conditioner — DOE BTU, not the box number
Two traps sink most AC purchases. First, portable-AC BTU is inflated on the box. The big "14,000 BTU" number is the old ASHRAE rating; the honest figure is the newer DOE (SACC) rating, which is typically 20–35% lower because it accounts for the heat the exhaust hose leaks back into the room. A "14,000 BTU ASHRAE" portable is really ~9,500–10,000 BTU DOE. This tool uses the DOE number for every unit so window and portable AC sit on the same honest axis — no apples-to-oranges. Second, bigger is not better. An oversized AC cools the air fast then shuts off before it removes humidity, leaving you cold and clammy and short-cycling the compressor. Match BTU to the room, don't overshoot. A rough guide: ~150 sq ft → 5,000 BTU, 350 sq ft → 8,000, 550 sq ft → 12,000, 700+ sq ft → 14,000+ (add capacity for sun, kitchens or high ceilings).
Window vs portable vs U-shaped: the form factor decides a lot
Window units are the efficiency and value default — the whole cold-making machine hangs outside, so nothing dumps heat back into the room. The downside is the install (they block the window and need a sill that fits) and, on old-style units, noise. Portable AC sits on the floor and vents through a hose to a window bracket — the only option when you can't mount in the window (casement windows, HOA rules, renters) — but that hose leakage is exactly why their DOE BTU is so much lower than their box number, and they're the least efficient and often the loudest. U-shaped window units (Midea U, Windmill) are the clever middle: the window sash closes through a slot in the U, putting the compressor outside the closed window — so they're dramatically quieter (the glass blocks the compressor noise) and far more efficient than a standard window unit, while installing like one. We keep form factor as a filter, not a scored column — pick what your window and rules allow, then let the Value Score rank within it.
CEER, inverter and noise: the specs that decide value
CEER (Combined Energy Efficiency Ratio) is the DOE's standardized efficiency rating — cooling output per watt, including standby — and it directly sets your running cost across a hot summer. Higher is better; ENERGY STAR units and inverters lead. Inverter compressors are the biggest quality jump in years: instead of slamming fully on and off, they ramp speed continuously to hold temperature — which means they're markedly quieter, steadier (no cold-then-warm cycling) and far more efficient. Nearly every top-scoring unit here is an inverter. Operating noise (dBA) is the spec people regret ignoring — a 52 dBA window rattler is fine in a den and miserable in a bedroom, while an inverter U-shaped unit at ~42 dBA is genuinely sleep-friendly. The tool scores all of these and normalizes to price, so a pricier inverter that's quiet and cheap to run can win on value — or lose to a simple window unit if all you want is cheap cooling for a garage.
Why we don't just name a single winner
The "best air conditioner" for a 600 sq ft sunlit great room is the wrong unit for a small bedroom you want silent, and the most efficient inverter is overkill for a garage you cool twice a week. Room size, window type, how much you care about noise, and up-front cost versus running cost all move the answer. One name buries that. The Value Score keeps the decision in your hands — filter to your form factor, weight what your room needs, and the formula is printed in the open right above.
The specs, briefly
DOE BTU = the honest cooling capacity (SACC for portables — lower than the ASHRAE box number; the real sizing figure). Coverage = rated room size in square feet. CEER = DOE efficiency, cooling per watt (higher = lower bills). Noise(dBA) = operating loudness (lower = bedroom-friendly). Inverter = variable-speed compressor (quieter + far more efficient). Type = window / U-shaped / portable (a fit choice, filtered not scored).
DOE BTU (SACC), CEER and ENERGY STAR status verified Sep 2026 against the ENERGY STAR Certified Room Air Conditioners dataset (pulled live from the SODA API) plus DOE ratings and manufacturer spec sheets; coverage, noise and inverter status come from manufacturer published figures and are flagged per-field where a spec sheet could not be re-fetched live. Portable-AC capacity is the DOE SACC rating, not the higher ASHRAE box number. Discontinued models were swapped for current SKUs (noted in the dataset). Prices are approximate street prices and fluctuate. Some links may be affiliate; that never changes the Value Score — the math runs on published specs, not payouts.