Portable Air Conditioner BTU Ratings Are Confusing. Here’s What You Should Know
When you buy i air conditionerBTU ratings are one of the first things people consider when deciding which unit to buy. But if you look at a portable air conditionerthose numbers can be confusing. In contrast window unitsportable models typically have two BTU ratings, the higher rating from the American Society of Heating, Refrigerating and Air-Conditioning Engineers and the lower one from the Department of Energy.
What do they both mean, and why are they important? Here’s everything you need to know before you buy a portable air conditioner for your home.
What is a BTU rating?
BTU stands for British thermal unit, a measure of heat energy. In addition to air conditioners, heat pumps again space heaters and have BTU ratings.
“A British thermal unit is the amount of energy required to raise one pound of water by one degree Fahrenheit,” Bryan Adams, CNET’s senior lab engineer and former HVAC configuration manager, explains.
As a rule of thumb, he says, BTUs are directly related to the size of the space you need to cool.
Why do portable AC units have two BTU ratings?
Initially, portable air conditioners were sold with a single BTU rating based on ASHRAE laboratory testing standards. Those ratings were often very high, such as 14,000 BTUs, but did not accurately reflect the actual cooling performance of the unit outside the lab.
In response, DOE introduced new testing procedures for portable AC units in 2017 to accurately measure cooling performance. The updated test measures performance across two different temperature and humidity tests and accounts for unit inefficiencies to provide a more accurate, seasonally adjusted cooling capacity rating, or SACC rating.
“The Department of Energy had to step in and fix the classification of HVAC control systems in terms of their cooling efficiency, and that’s something that never happened,” Adams said.
The fix comes down to how portable AC units work. Unlike a window air conditioner, a portable unit is located entirely inside the home and exhausts heat outside through a duct that connects to the window. During the cooling process, it can draw in already cooled air and push it out, reducing its efficiency.
“Because of all the energy you’re wasting on recooling or venting you’re already healing, it’s true [BTU] the number is usually between 25% and 40% less [than the ASHRAE rating],” Adams said.
This is why portable AC units often feature two BTU ratings. One shows the old ASHRAE rating, while the updated DOE rating shows more accurate cooling performance. Some older models only include ASHRAE ratings, which is why newer models have both ratings to avoid confusing consumers.
How many BTUs do you need?
The 8,000-BTU Black & Decker BPP08WTB is CNET’s budget pick.
Choosing the right BTU rating depends on the space you want to cool. The most important factor is the size of the room, but exposure to the sun, insulation and ceiling height should be considered.
If you’re not sure which BTU rating you need, an online BTU calculator can help. Ultimately, one BTU rating is not better than another. The right choice depends entirely on your location. If you choose too low for your needs, it will not cool the room properly, while too high can lead to wasted energy and increased costs.
