Could you interchange 10k BTU air conditioner with 2 5k BTU air conditioner and get the same result? Or is there a reason why buying one 10k BTU air conditioner is better than having 2 5k BTU air conditioners.

  • 1
    the most likely answer would be power draw I would say I'm not a sparky but I'm guessing running two unit would be less economical than running one, but this would depend on the individual situation, like is there a need to cool only one part not both etc.
    – UNECS
    May 24, 2012 at 1:57
  • Are you referring to window units? You want to size them based on the space being cooled. 2 5k units would be better at cooling 2 rooms than one 10k unit would be.
    – DA01
    May 24, 2012 at 3:09
  • @DA01 Yep they are both window units, and it's a one large room I need to cool
    – Ichiro
    May 24, 2012 at 11:23
  • 3
    Efficiency wise, one large unit + an oscillating or ceiling fan would probably be better. In terms of your back, two smaller units would probably be better ;)
    – DA01
    May 24, 2012 at 14:06
  • Isn't it about this : There is one big room I want to cool down. When I have one 5K BTU unit and would add a second 5K BTU unit will it a) cool down the room double as fast ? b) not cool better than just one 5K BTU but use double the electricity? c) cool down the room double as fast with double the electricity cost? d) cool down room double as fast with less electricity cost? I have the same question trying to find an answer before I am throwing my dollars into the wind so to say. Any thermo-dynamical-physics-knowledgeable person out there ?? Thank you
    – Kinko
    Jun 4, 2020 at 23:12

3 Answers 3


The 10k A/C will have a larger compressor, but only one fan, one control circuit, etc. Two 5k A/Cs will have two smaller compressors, two of everything.

I suspect that as a result, the 10k will be more efficient overall. What you should look at is the power consumption of each - then double the 5k. I expect that overall the 10k will run for less than 2 5ks - but I may be wrong. Depends on the power drain of the various components...

  • 2
    If you are talking about central A/C units. It would also depend on the configuration of zones, if zones were used. One unit might be cooling a shaded section of house, while the other cools a sunny part of the house. One thermostat might be set slightly warmer than the other, or there might be more heat producing appliances (and/or people) in one zone.
    – Tester101
    May 24, 2012 at 11:52
  • Well he's talking about window units... so zones are somewhat dynamic... May 24, 2012 at 12:38
  • The advantages of two units would be zoning the house to best balance the temperatures, as well as avoid 100% down time. If one needed repair the other could could possibly still run, and offer some comfort in the down time.
    – Matt Adams
    Nov 13, 2012 at 23:50

If one 5k unit will often be sufficient in your climate/room situation, it would be more efficient, as it will run longer cycles and lower the humidity better than the 10k unit (humidity is a key function of warm-weather comfort). If it's likely that both will be required often, then I would look at the specs; Greenbo is probably right in his analysis, but the specs would tell you for sure.


Each window unit partially obscures a window so if you value the natural light or the view, get a single 10 kBTU/h unit.

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