This will be my first time purchasing a window unit, and I'm a little confused. Most charts indicate that a 7,000 BTU unit is appropriate for a ~250 square foot room, however from what I can tell, these do not exist (only 6,000 and 8,000 BTUs are available). Also, none of the guides I see mention ceiling height, which I figured would be important (i.e. cubic footage seems more appropriate than square footage). Finally, many say that getting a unit that is too powerful actually won't cool as effectively, but don't really explain what this means exactly - if I put a 20,000 BTU unit in a 100 square foot room, would the room really be warmer than it would be with a 5,000 BTU unit? Or do they just mean that it would be overkill? Finally, some 6000 BTU units, like the GE AEL06LS say that they are only appropriate for 150 square foot rooms, and I don't understand why. Anyway, my room that is 233 square feet, with ~9.5 foot ceilings. Would it be best to get a 6000 BTU unit or a 8000 BTU unit?

The EPA has room size to BTU chart with some caveats for certain situations: Room size A/C size 100 up to 150 -> 5,000 BTU/hr 150 up to 250 -> 6,000 BTU/hr 250 up to 300 -> 7,000 BTU/hr 300 up to 350 -> 8,000 BTU/hr 350 up to 400 -> 9,000 BTU/hr 400 up to 450 -> 10,000 BTU/hr 450 up to 550 -> 12,000 BTU/hr 550 up to 700 -> 14,000 BTU/hr 700 up to 1,000 -> 18,000 BTU/hr 1,000 up to 1,200 -> 21,000 BTU/hr 1,200 up to 1,400 -> 23,000 BTU/hr 1,400 up to 1,500 -> 24,000 BTU/hr 1,500 up to 2,000 -> 30,000 BTU/hr 2,000 up to 2,500 -> 34,000 BTU/hr Make any adjustments for the following circumstances: Consider where you install the unit. If you are mounting an air conditioner near the corner of a room, look for a unit that can send the airflow in the right direction. If you fall into any of those special situations, that may help you with sizing. Otherwise, since you're between sizes of available units, unless your climate is particularly mild, I'd go up a size to allow a bit extra cooling capacity for hot days.

Height doesn't matter because cold air sinks. Regardless of the ceiling height, you only need to cool the bottom 6-7 feet.is my ac unit too big And none of these "room size basis" metrics pay any attention to the question of "what is the insulation level" "how much solar heat gain is there" "what is the window area and insulation"...since most consumers don't know - so they have handy rules of thumb...air conditioning unit with hose Room height does not matter so much unless you are 9 feet tall.stand up air conditioner units Do you think (or have reason to believe) the room is well insulated, or not? Does it get absurdly hot from the sun on a regular basis, or not? If well insulated and not a solar oven, go 5-6,000;

if poorly insulated, go 8,000; if a solar oven, go 8,000. Don't go 12,000 unless it's terribly insulated AND a solar oven... One problem with oversizing is poor dehumidification. @statueuphemism's comment has a good handle on the other.Today’s air conditioners come in several different sizes, whether they are a central air conditioner, a stand alone air conditioner or a window air conditioner. To have your air conditioning in your home run at peak efficiency you should size it to the area you are trying to cool. In order to figure out the correct cooling area you will need to measure all areas you are trying to cool. This will give you a close estimate on what size air conditioner you will need to keep you cool. In order to calculate this you will need to multiply the length times the width of the rooms you will be cooling. Once you have that number you can multiply that total time 25 BTU. This will give you excellent cooling whether it’s a sunny hot day, humid day or a moist day.

Here is an example of figuring out what BTU is appropriate for your cooling demands. If the room you are trying to cool is 14 feet wide by 16 feet long that would mean you have 224 square feet. So we will take the 224 and times it by 25 BTU per square foot. So 224×25 = 5600 BTU’s. This is the minimum you would want to use to efficiently cool your room. So what would happen if you were to use an air conditioner that is to small or to large. An air conditioning unit that is rated for less BTU’s will want to continually run so it can keep up trying to meet the cooling needs required. This will make your electric bill go up and will not effectively cool the room. A larger air conditioning unit can be overkill. In the air conditioning business bigger is not better. An air conditioner that is too large for the area will cool more quickly, but that is not always best when trying to properly cool a room. When your air conditioner is on and cooling the room, it is also extracting moisture from the air.

Moisture in the air is humidity which makes us feel hot and sticky. Even though the air will be cooler in a short amount of time, it does not give the air conditioning unit time to extract the moisture out of the air. So to properly calculate the size of the air conditioner you will require, measure the area to be cooled and take this information to an air conditioning company or an appliance store where they can make the proper recommendations on what size air conditioner will best suit you. Looking for a Portable Air Conditioner? BTU Makes a Difference in Decorating on April 14, 2010 by Staff Writer Portable air conditioner BTUs make all the difference between whether you’ll have a unit that cools your room well or one that works poorly. You might be tempted to go with the cheapest unit that you can find at the store. Let’s face it, these units can be expensive and cost more than what many renters can afford. However, you can make up the costs later in the savings you get from using less energy than a heat, ventilation and air conditioning (HVAC) system, central air conditioning and some window units.

If you get a unit with insufficient BTUs though, you won’t enjoy any savings in your electricity bill. British thermal units (BTUs) indicate how fast an air conditioner can cool a room. It measures the amount of heat (how many BTUs) that the air conditioner removes from the air. Portable conditioners with BTUs that are too low for a room’s size won’t cool all of the room, because it can’t. The higher the BTUs, the larger the room size it can cool. If you purchase a portable air conditioner that has too many BTUs for the room, then you’ll be using much more power than you need, which results in higher bills from your electric company. Your goal when shopping around for a unit is to find the air conditioner with the right number of BTUs for the room size. Each air conditioner lists the BTUs in its product description online or on the box, which corresponds to a maximum room size. 5,000 BTU Portable Air Conditioner Expect a portable air conditioner with 5,000 BTUs to cool a room that’s no more than 175 square feet.

Try to find one with a dual hose to cool the room even faster. Variation in temperature control settings is also key, and you should make sure that the portable air conditioner that you’re considering has one. If you want to cool a room that’s 200 square feet, then you’ll need a portable air conditioner with 8,000 BTUs. If you have enough money to buy one with a self-evaporative system, that’s even better. You won’t have to worry about emptying out trays every day, which is the case with non-evaporative units. Living room areas or large bedrooms that are around 300 square feet will need a portable air conditioner with 10,000 BTUs. Some units include a built-in shut on/shut off thermostat to help you conserve energy. You can also set it to come on minutes before you come home from school or work. A portable air conditioner with 12,000 BTUs can cool a room up to 400 square feet. If you need to heat your room as well, consider a 2-in-1 air conditioner and heater combination.