We have a very old (20-25 years old) window ac unit in the living room and I'm trying to figure out how efficient it is. I can't find out the model number or any statistics about it. The manufacturer website doesn't have any info about old models either.

I can measure the KWh consumption, but that won't be of any use without a way to figure out its BTU. Any creative suggestions on how I can measure that?

Alternatively, just some historical data on window ac's from that time period, like their average COP, would be really helpful.

  • Can you not find the unit's nameplate? Oct 8, 2017 at 12:47
  • Hello, and welcome to Stack Exchange. A related question I've been wondering about: do air conditioners degrade over time? If so, then the original efficiency may be an overestimate of its current efficiency. Oct 8, 2017 at 19:10
  • i would measure it and calc it from a known. Lets say a 5000x model drop the room 10 deg F from 70 in 10 mins. If the unknown one takes 5 mins to do the same, you can figure it's 10000x...
    – dandavis
    Oct 8, 2017 at 20:33

1 Answer 1


The 10 SEER minimum was right around that time period so it would most likely be 8 or 10 SEER. Window air conditioners at that time were listed as appliances and were not subject to testing so manufacturers could make up any numbers they wanted to. The BTU ratings would be all over the place in those days. You could take two 12000 btu air conditioners and one would cool considerably better than the other. And since EER is basically BTU/Watts then a change in the BTU would be a change in the EER. Air conditioners also loose their efficiency over time since it is a function of how it can transfer heat and the heat exchanging coils will delaminate over time. Not usually fully but there will be oxidation forming between the copper tubes and the aluminum fins.

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