Choosing a Portable Air Conditioning Unit: Room Air Conditioner

Learn How To Select Portable Air Conditioning Units for Any Room of the House

Woman with air conditioner

A portable room air conditioner is exactly what it sounds like - a freestanding air conditioner that doesn't stay in the wall or window but can be moved throughout the home or office. Because portable air conditioners are not part of a central system, you can more easily direct the cool air exactly where you want it; in fact, portable air conditioners are frequently used to supplement central air conditioning. One of the most common uses is to cool computer server rooms. Here are some tips on how to choose a portable air conditioner.

  1. What is a BTU? We're going to discuss BTUs now but don't tense up-it's really quite a simple concept in a portable air conditioning unit. A BTU (or British Thermal Unit) is the amount of heat necessary to raise the temperature of one pound off water by one degree Fahrenheit. Air conditioners have BTU ratings-the higher the BTU, the faster the air conditioner can cool a room.
  2. BTU Ratings. The most important decision you will make in choosing your air conditioner is getting an air conditioner with the appropriate BTU rating. If the BTU rating is too high, your air conditioner can actually freeze over though many come with an automatic shut-off switch should the unit begin to get too cold. If the BTU rating is too low, the air conditioner will not be able to cool the room adequately. The way that the rating works is that a 5,000 BTU air conditioner removes 5,000 BTUs of heat per hour. Keep in mind that a person at rest adds approximately 230 BTUs to a room per hour so that needs to be factored in to your portable air conditioning purchase.
  3. Calculating Square Footage. A method that is frequently used to determine the appropriate BTU rating for an air conditioner is to calculate the square footage of the room you intend to cool. To do this, measure the area that you are interested in cooling. Multiply the width of the room by the length of the room to determine the room's square footage. You will need approximately 30 BTUs per square foot of space.
  4. HVAC Engineer Method. While the calculation described above is a simple one that an ordinary homeowner can perform easily, heating, ventilation and air conditioning (HVAC) professionals would argue that variables such as the placement of walls and windows, the differences between surface areas of one- and two-story homes, the differences in air flow and insulation among different buildings, the number of occupants, and other such factors require more precise calculations, such as those described at HomeEnergy, a nonprofit organization that disseminates information on residential energy efficiency, performance, comfort, and affordability.

    If I were investing in a central system, I would absolutely get my BTU rating spot on, but for a portable air conditioner, I would use the rule of thumb calculation described in #3 and just bump the BTU rating up a notch if your room faces south, is not well insulated or has a high ceiling (but mind you, I am not a HVAC engineer).

  5. Size and Weight. Portable air conditioners come in a variety of shapes and sizes but tend to range between 28 to 36 inches tall. Remember that portable air conditioners are heavy so keep the unit's weight in mind, particularly if you intend to be carting it up and down the stairs.
  6. Extras. Portable air conditioners come with programmable timers, built-in air filters, dehumidifiers or water reservoirs, exhaust hoses and accessories for venting--it's up to you to decide which extras you'd like and how much they're worth to you.

It won't be long now until you can chill. Portable air conditioning units are worth every dime. But please remember that after you choose your unit, it is important to vent it properly.


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