So you’re in the market for a new AC unit.  There are few things that you really need to know before you make that purchase.  Some basic questions and measurements will ensure that you are getting the right size unit for the job.


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BTU is actually the abbreviation of British thermal units.  This is the measurement of the amount of energy needed to change the temperature of one pound of water by one degree.  So, checking for BTUs basically means you will be matching the cooling power of the unit, to the room you need to cool, and in some cases heat as well.  That’s one of the most important considerations.  An air conditioner controls the climate by both cooling the air, and by removing the moisture in the air too.  If your AC isn’t powerful enough, your room will never get cool even though the unit runs all the time.  And if your air conditioner has too many BTUs for your room size room, it will cycle off after cooling quickly.  And that means too quickly to be able to remove the moisture, making your room feel cold and clammy.


So measure the square footage of your room.  Square footage means the length of the room times its width.  A standard twelve by fifteen room is one hundred eighty square feet.  Then multiply the area times 30, in this case, that’s 5400.  That’s the starting BTUs needed for the room’s AC unit.

But you’ll want to measure your ceilings, too.  For each foot over eight feet, add a thousand BTUs.  If the ceilings are lower than 8 feet, like in a basement, deduct 1000 BTUs.  And if it’s a kitchen, just increase by 50%, the BTUs you’ve calculated. If you are cooling two rooms like an open living room/dining room floor plan, there must be an open arch connecting the areas.  Measure both rooms and add them together, then multiply as if one room.   If the rooms are separated by a door, treat them like two separate rooms.  That doorway is just too narrow to allow the cool air to get through.


What floor is the room located on, that needs to be cooled?  If the room is on the top floor under the roof, you’ll need to check for insulation.  If the attic is insulated, use the standard measuring method (length x width x 30) and then increase the BTUs by 15%.  If there is no insulation, the BTUs should be increased by 25%.

The number of people normally using the room is also a consideration.  For instance, The BTUs under the normal measuring mode assumes 2 people using the room most of the time.  If more than 2 people normally occupy the room to be cooled add 600 BTUs for each person.  AND, if the room gets a lot of sun, the BTUs should be increased by 10%.

With all of these measurements, it’s important to know that the BTUs on the units will be rounded up or down, based on the size of the units available.  For example if your measurements come to 9,000 BTUs, you would round up to a 10,000 BTU unit.  If your area calls for 6,300 BTUs, it is closer to round down to 6,000.


What type outlets do you have where the AC will be placed – 115V or 230?  Knowing which type outlet is very important.  Too many amps onto a branch circuit will trip the breaker (or blow a fuse). If there is a single outlet it is likely a dedicated line, meaning the air conditioner will have its own circuit breaker or fuse.  Nothing else in the room will affect the unit.  If there is a duplex outlet, you will need a 115 volt unit with a maximum 7.7 Amps.


What type window opening do you have?  Some units are designed to only fit in a “double hung” standard “up and down” window.  Also make sure you check to make sure your unit comes with an installation kit.  In some cases, it is an optional accessory, as many units are now actually installed through the wall for year round use (heat and cool models).

Various units may be installed using the entire window kit, one side panel, and sometimes using no side panels.

Remember to MEASURE CAREFULLY:  If your AC is smaller than your window, there are always panels to help it fit snugly but there aren’t many good options if your window is smaller than the AC unit.    So measure twice … and write it down. 

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There are two types of wall units. The major difference between the two is the louvers on the side.  An air conditioner with louvers is actually a window unit with a “slide out chassis”.  This lets you slide out the chassis from the shell otherwise known as a sleeve, case or cabinet.  The shell can then be installed through the wall just as long as the thickness of the wall does not block the louvers, as the louvers are how the unit “breathes”   The most important thing to know for through the wall installation is the shell depth to louvers.  This tells you how much solid part of the sleeve there is from the front to the start of the louvers.  The thickness of the wall cannot exceed this dimension or it will interfere with the louvers, preventing the unit from working properly.  This will have a negative effect on the unit performance, efficiency and overall longevity.

If this is a replacement unit, there will be an existing sleeve or shell where the wall units attach.  Check to make sure you have the brand of the sleeve, as different manufacturer models fit differently into sleeves.  You may have to match the manufacturer of the original unit to your existing sleeve.

It’s important that you check the new AC unit for which direction the air is discharged, and compare to where the unit will be placed.    Some models discharge air at a 45 degree angle and if the unit is mounted too close to the ceiling, the unit will not perform adequately as the air will be hitting the ceiling.

Make sure the air can flow freely, with nothing blocking the vents wherever you place the unit.   You definitely do not want the air to be blowing directly against another wall or your AC will constantly cycle.  


No place for a window or wall unit?  Check out the newer portable models that actually can move around from room to room.  While a bit more expensive than a stationery wall or window unit, it’s portable and can be used quickly to cool down areas room by room.  The units are quiet and efficient.  That’s great for a large gathering, or older homes with little insulation.

Above content provided by BrandsMart USA








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