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When shopping for a purchase air conditionerBTU ratings are one of the first specifications people consider when deciding which unit to purchase. But if you look at a Portable air conditionerThese numbers can get very confusing. Unlike Window unitsportable models often have two BTU ratings, a higher rating from the American Society of Heating, Refrigerating and Air-Conditioning Engineers and a lower rating from the Department of Energy.
What do they both mean, and why do they matter? Here’s everything you should know before purchasing a portable air conditioner for your home.
What is the BTU rating?
BTU stands for British Thermal Unit, and is a measurement of thermal energy. In addition to air conditioners, Heat pumps and Space heaters It also has BTU ratings.
“A British thermal unit is the amount of energy needed to raise one pound of water by one degree Fahrenheit,” explained Brian Adams, CNET’s senior laboratory engineer and former director of HVAC configuration.
As a general rule, BTUs are directly related to the size of the space you need to cool, he says.
Why do portable air conditioning units have two BTU ratings?
Originally, portable air conditioners were sold with a single BTU rating based on ASHRAE laboratory testing standards. These ratings were often very high, such as 14,000 BTU, but did not always accurately reflect the unit’s real-world cooling performance outside the laboratory.
In response, the Department of Energy provided New testing procedures for portable air conditioning units in 2017 to accurately measure cooling performance. The updated test measures performance across two different temperature and humidity tests and takes into account unit deficiencies to provide a more accurate rating and seasonally adjusted cooling capacity, or SACC, rating.
“The Department of Energy had to step in and correct HVAC regulators’ classification of cooling efficiency, which is largely unprecedented,” Adams said.
The correction goes back to how portable AC units actually work. Unlike a window air conditioner, a portable unit is located entirely inside the home and vents heat outside through a hose attached to the window. During the cooling process, it can pull in some of the air that has already been cooled and push it out, reducing its efficiency.
“Because of all the energy you waste recooling or venting air you’ve already treated, the true number (BTU) is usually 25% to 40% lower (than the ASHRAE rating),” Adams said.
That’s why portable AC units often feature two BTU ratings. One reflects the older ASHRAE rating, while the updated DOE rating shows more accurate cooling performance. Some older models only have ASHRAE ratings, which is why newer models have both ratings to avoid confusing buyers.
How many BTUs do you need?
The Black & Decker BPP08WTB 8,000 BTU is CNET’s budget pick.
Choosing the appropriate BTU rating depends on the space you want to cool. The most important factor is the size of the room, but sun exposure, insulation and ceiling height must also be considered.
If you are not sure which BTU rating you need, Online BTU calculator can help. In the end, one BTU rating is not better than another. The right choice depends entirely on your space. If you choose one that is too low for your needs, it will not cool the room properly, while one that is too high may waste energy and increase costs.
