On this page
- Size the Unit to the Bedroom's Square Footage
- Adjust the Chart Figure for Shade, Sun and People
- Why a Bigger Unit Can Leave a Bedroom Feeling Clammy
- Window Unit or Portable for a Bedroom?
- Keep Night Noise in Check
- Moisture, Dryness and the Water a Portable Collects
- Sleep Mode, Timers and a Dim Display
- Set the Room Up Before Blaming the Unit
- When the Bedroom Still Will Not Cool
- Which to choose
- Questions people ask
Size the Unit to the Bedroom's Square Footage
A bedroom is sized like any other room. Measure the length and the width in feet, multiply the two numbers, and match the result to a capacity chart. The table below is the ENERGY STAR chart, and its figures assume an 8-foot ceiling. A room of 150 up to 250 sq ft calls for 6,000 BTU per hour, while 250 up to 300 sq ft calls for 7,000.
Many bedrooms land in the smaller rows of that chart. After the adjustments covered below, round down to the nearest thousand rather than up. Extra capacity does not produce better cooling, and the guide to choosing BTU for room size walks through the arithmetic step by step.
| Area to be cooled (sq ft) | Capacity needed (BTU per hour) |
|---|---|
| 100 up to 150 | 5,000 |
| 150 up to 250 | 6,000 |
| 250 up to 300 | 7,000 |
| 300 up to 350 | 8,000 |
| 350 up to 400 | 9,000 |
| 400 up to 450 | 10,000 |
Adjust the Chart Figure for Shade, Sun and People
The chart is a starting point, and ENERGY STAR lists four adjustments that change it. A heavily shaded room takes 10 percent less capacity, a very sunny room takes 10 percent more, each person beyond two adds 600 BTU per hour, and a kitchen adds 4,000 BTU. A bedroom is rarely a kitchen, but the shade and people lines apply directly.
A north-facing bedroom under a tree may need less than the chart says, while a top-floor room with an unshaded west window may need more. The explainer on heat gain from windows and insulation covers why two rooms of the same size can behave differently.
| Condition | Adjustment |
|---|---|
| Room is heavily shaded | Reduce capacity by 10 percent |
| Room is very sunny | Increase capacity by 10 percent |
| More than two people regularly in the room | Add 600 BTU per hour for each additional person |
| Unit is used in a kitchen | Add 4,000 BTU |
Why a Bigger Unit Can Leave a Bedroom Feeling Clammy
An air conditioner removes heat and moisture at the same time. ENERGY STAR warns that an oversized unit cools the air before it has a chance to remove the humidity, which leaves the room feeling damp and clammy. Choosing a larger unit than the chart calls for does not give better cooling.
Midea makes the same point from the other direction: an air conditioner is also a dehumidifier, its cold coils condense water out of the room, and a room that becomes very dry can be a sign that the unit is too large for the space. If the bedroom feels clammy, check the capacity against the square footage before changing anything else. The explainer on oversized units goes further.
Window Unit or Portable for a Bedroom?
Window units are compared on the BTU figure the listing states. Portable units are compared on seasonally adjusted cooling capacity, the U.S. Department of Energy figure, and a portable whose maker lists no such figure cannot be lined up against another portable's adjusted number. The explainer on BTU and SACC ratings sets out the difference.
For a bedroom, the shape of a window unit matters as much as the capacity. ENERGY STAR describes U-shaped and saddle-style models that bracket the windowsill instead of sitting on top of it: the window can still open and close, the control panel and vent sit inside, and the compressor sits outside the room. That last point is the one to weigh at night. The comparison of standard and U-shaped units covers the trade-offs.
Keep Night Noise in Check
Midea's window AC FAQ says a unit should be audible while running but not louder than speaking volume, and it lists the sounds that are normal: air moving, refrigerant gurgling, the compressor humming, water splashing, and the controls clicking or beeping.
Placement changes what you hear. Whynter's portable AC guidance says to move a noisy unit to a spot with a level, hard floor. For a window unit, the U-shaped design described above moves the compressor outdoors. The explainer on window AC noise indoors and outdoors explains which parts of the sound travel where.
Moisture, Dryness and the Water a Portable Collects
A bedroom unit pulls water out of the air as it cools, and where that water goes depends on the design. A window unit drains condensate to the outside when it is tilted correctly; Midea's FAQ says the unit should sit slightly tilted backward so water flows to the rear.
A portable collects water in an internal reservoir. Whynter's troubleshooting guide describes the symptom of a full reservoir: a red light flashing and STOP or P1 on the display, cleared by draining the lower drain port. Some models use a rubber stopper and others a plastic cover plus stopper, so the manual for the specific model is the reference. The explainer on how portable ACs handle water covers the options.
Sleep Mode, Timers and a Dim Display
Sleep mode is built for exactly this setting. In the Midea MAW06R1WWT manual, sleep mode raises the set temperature by 2°F thirty minutes after it is selected, raises it another 2°F after another thirty minutes, holds that setting for seven hours, then returns to the temperature originally selected. The same manual lists a settable range of 62°F to 86°F.
Two other details matter at night. The manual's check filter light comes on after 250 hours of operation, which is a reminder rather than a fault. A display that stays bright can also be worth dimming, and the explainer on display dimming for bedrooms covers what units offer. The sleep mode explainer compares the schedules different makers use.
Set the Room Up Before Blaming the Unit
Frigidaire's support page lists the setup items that decide whether a bedroom cools: the room should be enclosed and insulated, windows and doors closed, and the unit's side curtains and the window framing around it closed up. Whynter's guide adds that heat-producing appliances in the room work against the unit. The same page notes that a working unit drops the temperature of the air it pulls in by 17 to 20°F before blowing it back out.
Midea's FAQ mentions the black foam strips that come with its window units: they wedge between the front and back window sash to block air passing through. Whynter's guide adds that starting the unit earlier in the day works better than switching it on at the hottest point, and that a portable's exhaust hose should stay as short and straight as possible, never longer than 9 feet, with at least 20 inches of clearance at the air intake.
When the Bedroom Still Will Not Cool
Run through the basics first: the unit is in cool mode, the set temperature is below room temperature, the filter is clean, and nothing blocks the front or the back. Midea's FAQ names a restricted air filter and blocked airflow as the usual reasons a unit shuts off before the room reaches the set temperature. The checks for a room AC that is not cooling enough lists the rest.
If those checks pass, the maker's route is service. Frigidaire's support page sends owners of units installed within the past 30 days back to the installer and directs everyone else to contact the company to schedule service. Midea's manual for the MAW06R1WWT lists AS as a room temperature sensor error and ES as an evaporator temperature sensor error, and says to call for service if either repeats.
Which to choose
| If you | Look for |
|---|---|
| If the bedroom is 150 up to 250 sq ft | Look for 6,000 BTU per hour on the chart, then apply the shade and people adjustments and round down. |
| If the window is heavily shaded | Reduce the chart figure by 10 percent before rounding down. |
| If two people or fewer use the room | Skip the people adjustment; 600 BTU per hour is added only for each person beyond two. |
| If the room feels damp and clammy | Check whether the unit is oversized, since a unit that is too large cools the air before it removes moisture. |
| If the room feels very dry | Compare the capacity with the square footage, because Midea notes that a unit too large for the room can dry it out. |
| If noise wakes you at night | Consider a U-shaped window unit, which ENERGY STAR describes as placing the compressor outside the room. |
| If you want the room to warm slightly overnight | Look for a sleep mode that raises the set temperature in steps and returns to the original setting in the morning. |
| If you are choosing a portable | Compare seasonally adjusted cooling capacity, and treat a model whose maker lists none as not comparable on that figure. |
Questions people ask
What size air conditioner does a bedroom need?
Work from the square footage. The ENERGY STAR chart, based on an 8-foot ceiling, gives 5,000 BTU per hour for 100 up to 150 sq ft and 6,000 for 150 up to 250 sq ft. Apply the shade, sun and people adjustments, then round down to the nearest thousand.
Does a bigger unit cool a bedroom faster?
It can drop the air temperature quickly, but ENERGY STAR warns that an oversized unit cools the room before it removes humidity, leaving the air damp and clammy. A unit matched to the square footage gives better comfort.
Why does the bedroom feel dry with the AC running?
An air conditioner is also a dehumidifier: its cold coils condense moisture out of the air. Midea notes that a room that becomes very dry can point to a unit that is too large for the space, so check the capacity against the square footage.
Is a portable or a window unit quieter in a bedroom?
It depends on the design rather than the category. ENERGY STAR describes U-shaped window units as providing greater noise reduction because the compressor sits outside the room. A portable sits inside the room, so placing it on a level, hard floor matters, as Whynter's guidance notes.
What temperature should the unit be set to overnight?
The Midea MAW06R1WWT manual lists a settable range of 62°F to 86°F. Its sleep mode raises the set temperature by 2°F after thirty minutes, another 2°F after another thirty minutes, holds that for seven hours, then returns to the original setting.
Why does a portable AC stop with a full tank message?
Whynter's guide describes a flashing red light with STOP or P1 on the display, which means the internal reservoir is full. Draining the lower drain port clears it; if the message stays after draining, the maker says to contact support.
Should a window unit come out for winter?
ENERGY STAR suggests removing the unit at the end of the cooling season if possible, to reduce heat loss, or covering it with an appropriately sized cover. The guide to taking down and storing a window AC covers the sequence.