Room Air Conditioner Terms in Plain English

Four kinds of terms on one listing

A room air conditioner listing mixes four kinds of shorthand: how much cooling a unit delivers, how efficiently it delivers it, how air and water move through the cabinet, and what the controls and cord parts are called. Each answers a different question, and mixing them up is the usual reason two units look comparable when they are not.

The table gives the short version. The sections after it take each term in turn.

BTU: the capacity number

BTU stands for British thermal unit, and on a room air conditioner the figure means BTU per hour: how much heat the unit can pull from a room in an hour. The ENERGY STAR sizing chart pairs 100 to 150 sq ft with 5,000 BTU, 300 to 350 sq ft with 8,000 BTU and 450 to 550 sq ft with 12,000 BTU, figured on an 8-foot ceiling.

The chart comes with adjustments. A heavily shaded room takes 10 percent less capacity, a very sunny one 10 percent more, each person beyond two adds 600 BTU, and a kitchen adds 4,000 BTU. Those adjustments matter, because an oversized unit cools the air before it can pull out humidity, leaving a room damp and clammy.

Window units are compared on this BTU figure. The BTU ratings guide walks through the chart, and choosing BTU for room size covers the adjustments.

SACC: the capacity number for portables

SACC stands for seasonally adjusted cooling capacity, the Department of Energy figure for portable air conditioners in Btu per hour. The federal standard is written around it: single-speed portables are rated on SACC and variable-speed portables on SACC Full, as determined under the DOE procedure.

A portable's carton may carry a larger BTU number than its SACC, because the two are measured differently. Rank portables on SACC only, and when a maker lists no SACC for a model, treat the capacity as unknown rather than borrowing the BTU figure. Never convert one into the other.

Portable vs window AC explains why the portable number tends to look smaller.

CEER: the efficiency number

CEER is the combined energy efficiency ratio, written in Btu per watt-hour. It answers how much cooling a unit delivers for the energy it draws, so a higher CEER means more cooling per unit of energy.

ENERGY STAR sets base CEER levels that change with capacity and unit type. Its criteria table has a separate column for units with louvered sides and separate rows for casement-only and casement-slider models, so a CEER that clears the bar in one size class may not clear it in another. Compare CEER only between units of similar capacity and type.

The CEER explainer goes through the ratio itself.

Variable speed and fixed speed

A fixed-speed room air conditioner runs its compressor at one level: full output while the thermostat calls for cooling, and off once the set temperature is reached. A variable speed compressor instead changes the speed of its motor to hold the temperature continuously.

ENERGY STAR says variable speed models cool quietly and use notably less energy, and that such models can earn the certification. The practical difference is fewer full-power starts and a steadier room temperature.

The inverter vs fixed-speed comparison sets the two designs side by side.

Louvers, louvered sides and casement units

Louvers are the vanes at the air outlet. Midea's manual for the MAW06R1WWT lists improperly positioned louvers among the reasons a unit cools but the room stays warm, and advises positioning them for better air distribution. ENERGY STAR makes a related point: a unit mounted near a corner needs to be able to send airflow in the right direction.

Louvered sides are something else, the grille panels on the sides of a window unit's cabinet. ENERGY STAR's criteria separate units with louvered sides from those without, so the same capacity can carry a different base level.

Casement describes the window a unit is made for, not the cooling. ENERGY STAR lists casement-only and casement-slider units as their own categories. For other window styles, which window types take a window air conditioner covers the fit.

Slinger ring, drain plug and water terms

A window unit has no drain hole for everyday use. GE Appliances explains that a slinger ring around the rear fan blade picks water up off the bottom of the pan and throws it against the condenser coils, which helps cool the coils and helps clear condensation and rainwater. Water can still collect and drip outside in humid or rainy spells, which GE calls normal.

Some units look as though they have a drain plug at the bottom of the pan. GE says it should normally stay in place: it exists so water can be removed when the unit is stored for the season, or when a technician needs to drain it. Newer models may have a sub-base water plug that can be pulled during operation to reduce water at the back, at the cost of some efficiency, and to quiet the pinging of droplets on the coils.

Gurgling and water sounds sorts the normal noises from the rest.

The current detection device on the plug

The power cord on some room air conditioners carries a current detection device built into the plug end. Midea's manual for the MAW06R1WWT describes it: the cord contains the device, the reset button must be pushed in for correct operation, and a damaged cord cannot be repaired, only replaced.

If the device will not reset, the manual's instruction is to contact customer service rather than open anything up. The same manual points to the nameplate on the unit for voltage information and says installation must follow the included instructions.

Mode names and error codes

Mode names are shorthand too. Energy Saver keeps the fan running about 3 minutes after the compressor stops and then cycles it with the compressor; ENERGY STAR describes the mode as limiting fan operation when the compressor is off, and Midea's manual notes it starts automatically in Cool, Dry and Auto. Check Filter is a reminder light, set on the MAW06R1WWT to come on after 250 hours. Sleep raises the set temperature in steps, 2°F after 30 minutes on that model.

Dry mode makes the unit act as a dehumidifier, with some cooling as a side effect, according to the same manual. Error codes are the least portable vocabulary on the unit, because each maker assigns its own letters. Frigidaire's error code guide, for example, lists a room temperature sensor failure and a full bottom tray among the conditions its room air conditioners report, and directs owners to support if a code returns after a reset. Read the page for your own brand and model rather than assuming a code means the same thing across brands.

The eco and energy saver explainer covers the fan behavior, and reading error codes explains how to look up a code for a specific model.