Key Facts: Home Cooling
This page is Chill Factor Lab's maintained fact reference — the specification and rating facts our guides are built on, restated in plain prose. We report DOE/EnergyStar rating facts and manufacturer specifications, never invented figures.
BTU sizing
The baseline rule (ENERGY STAR/DOE) is roughly 20 BTU per square foot of room for average insulation and 8-foot ceilings. Real sizing adjusts from there: add about 4,000 BTU if a kitchen adjoins the room, add roughly 10% for heavy direct sun, add about 600 BTU per occupant beyond two, and add roughly 1,000 BTU per foot of ceiling height above 8 feet. Oversizing wastes money and can leave a room clammy because the unit short-cycles before dehumidifying; undersizing means the unit runs constantly and never catches up. Full table: How Many BTU Do I Need? and the master reference at The Cooling Numbers.
SACC vs ASHRAE BTU
Since a 2017 DOE rule, portable air conditioners must disclose a SACC (Seasonally Adjusted Cooling Capacity) rating alongside the older ASHRAE rating. ASHRAE tests at an ideal 80°F; SACC tests at 83°F/95°F, closer to real summer conditions, and factors in hose/duct losses. SACC typically runs 25–45% below the ASHRAE number for the same physical unit — a portable marketed as "14,000 BTU" can genuinely cool like an 8,000–9,500 SACC-rated machine. Always size a portable AC off the SACC figure. More in Why Portable ACs Underperform Their BTU Sticker.
CEER vs SEER vs EER
Window and portable air conditioners are rated in CEER (Combined Energy Efficiency Ratio) by the DOE — a single number, roughly 8–15 for current units, that folds in standby power draw with running efficiency; higher is more efficient. EER is the older, simpler standard CEER replaced for window units in 2014. SEER (and SEER2) is a seasonal rating used for central and split-system (mini-split) AC and does not apply to window or portable units at all, regardless of marketing language. Full decoder at SEER vs CEER Meaning.
Single-hose vs dual-hose portable AC
A single-hose portable AC exhausts room air outside through one hose, creating negative pressure that pulls warm replacement air back into the room through gaps around doors and windows — cutting real-world cooling by roughly 15–30% versus the unit's rated capacity. A dual-hose unit draws its intake air from outside instead, avoiding that pressure imbalance and running much closer to its rated capacity, at the cost of a second hose or a wider window kit. Details in Dual vs Single Hose Portable AC.
Fans don't cool rooms — they cool you
A fan does not lower a room's air temperature; a thermometer reads the same whether the fan is on or off. It speeds sweat evaporation and convective heat loss from skin, which is why running a fan in an empty room wastes electricity for zero benefit, and why fans are rated in CFM (airflow) and dB (noise) with no "cooling capacity" figure at all. Box and high-velocity floor fans move the most air (often 2,000–3,000+ CFM) but run loud (60–70+ dB); tower and pedestal fans trade airflow for quiet, better suited to bedrooms. More in Do Tower Fans Actually Cool a Room? and dB Noise Guide for Sleeping.
Evaporative (swamp) cooler humidity limits
Evaporative coolers work by evaporating water into passing air, which only pulls heat out effectively when the air can absorb more moisture. Below roughly 30% relative humidity they can drop room temperature 20–30°F; between 30–50% RH they're still meaningfully effective; above roughly 50–60% RH, cooling drops to about 5–10°F or less and the unit mostly adds humidity instead. This is a climate-geography limit, not a product-quality issue — the same unit that excels in a dry Southwest climate will disappoint in a humid Southeast or Midwest summer. Full climate breakdown in Swamp Cooler Climate Map.
How these facts are maintained
These facts are drawn from DOE rulemaking on portable-AC labeling (SACC, 2017) and room-AC efficiency ratings (CEER, EER), manufacturer-published specification sheets, and public HVAC-industry reference material on evaporative-cooling performance, reviewed against our guides and updated on the date shown above when a rule or typical range changes. We do not publish prices or star ratings, every pick names an honest drawback, and we never invent a certification or lab figure we haven't verified against a public source. Our full methodology is at How We Evaluate.