An air conditioner that’s too small never catches up. One that’s too big cools the room fast, shuts off before removing humidity, and leaves you cold and clammy while wearing out its own compressor.
Getting the size right matters more than most buying decisions, and it isn’t complicated once you know which adjustments apply to your space. These guides include the charts, the math, and the factors that change the answer: ceiling height, sun exposure, climate, and how many people are in the room. You’ll also find plain-language explanations of efficiency ratings, so you can tell which numbers on a spec sheet actually affect your bill.
The short answer to “what size air conditioner do I need” is roughly 20 BTU per square foot of space you’re cooling. A 500 square foot room needs about 10,000 BTU. That’s the starting point, not the answer. Ceiling height, sun exposure, how many people use the room and what climate you live in can…
The seasonal energy efficiency ratio, almost always shortened to SEER, tells you how much cooling a system delivers per unit of electricity it consumes over a typical cooling season. Higher number, less electricity for the same cooling. A 20 SEER unit uses roughly half the power of a 10 SEER unit doing the same work….