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My 150 square foot bedroom has central air and stays around 80 degrees F (sometimes a few degrees more or less).

8,000 BTU Results

I purchased a Frigidaire 8,000 BTU unit from the Home Depot to cool the room. It is able to keep the room at 68 to 72 degrees F and runs constantly (I have it set to 62 - it occasionally switches to fan only mode to let the compressor rest).

10,000 BTU Question

I would like to cool the room more and remove more humidity. The Home Depot sells the same series model in a 10,000 BTU variation. If I upgrade to 10,000 BTUs will I see a difference? I would like to get the room to stay at 64 to 68 degrees F at 50% or lower relative humidity.

I am guessing that the 10,000 BTU model will also run constantly (occasionally going to fan only mode) as it will never be able to reach the set temperature of 62 - I am fine with this as I am replacing my old unit which did the same thing and lasted for 8 years.

My understanding is that portable air conditioners have overrated BTUs as they are no where as efficient as window units because the compressor is inside the room.

  • All portable a/c units exhaust hot air to the outside through a hose, but if I understand correctly some portable units have a second hose which pulls in outside air to cool the condenser whereas others just use air from the conditioned space. Is this correct? What kind do you have? – Jim Stewart Jun 24 '17 at 5:16
  • Sounds like what you should actually do is get your central system serviced, upgrade your central system, or upgrade your insulation, if your central system is not doing the job. – Ecnerwal Jun 24 '17 at 12:16
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    Out of curiosity, why so cold? Server room? Also I'm not sure I agree that portables are less efficient, it all depends on how well they are vented. Being NOT blasted by the direct sun should make the unit more efficient. – Harper Jun 24 '17 at 15:05
  • You have a circuit that is able to power this 8000 BTU/h unit, but it may not be able to power a 10,000 BTU/h unit. If you would get a larger unit, you might trip a breaker that other people are depending on. There are continual improvements in efficiency of a/c units, but there is going to be a range of efficiency, probably reflected in cost of the unit. You should determine the power consumption of any unit you are considering for replacement. If it is greater than the existing unit, you might exceed the capacity of your power source. – Jim Stewart Jun 24 '17 at 15:19
  • Get a two-hose portable a/c unit. A single-hose portable a/c unit in one room of a building pumps not just heat out of your room, but also air out of the building. This leads to lower pressure in the building which will cause increased infiltration of outside air into the building, and will cause the central a/c unit to run more to compensate. – Jim Stewart Jun 24 '17 at 15:46
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Basically, a BTU is the amount of heat required to raise the temperature of one pound of water (at or near 39.2 degrees Fahrenheit) by one degree Fahrenheit

So, an AC unit with the capacity of 10,000 BTU's per hour can cool more air (a bigger room) at the same rate, or the same amount of air faster than a unit with a capacity of 8,000 BTU's per hour.

So, in the exact same room under the exact same conditions, the larger AC can maintain a lower temperature than the smaller one.

If you have the AC set at 62°F and it never reaches that temperature and shuts off then the unit is overloaded and has to rest the compressor to keep from freezing up. Or it is possible the freezestat is shutting the compressor off when the evaporator coil freezes up. Either way, setting it to 62° is futile since it apparently cannot get to that temperature.

It appears your current unit can only get to 68° so that would be your maximum low set point for that unit.

A larger unit should be able to get to a lower temperature under the same conditions. But it still may never make it to 62°.

Good luck!

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