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Ask Mr. Mr. Tight-Watt: AC vs. a Dehumidifier  Smart Choices Archive

Ask Mr. Mr. Tight-Watt: AC vs. a Dehumidifier

Make sure your AC is sized correctly for best operation.

Ask Mr. Tight-Watt

Mr. Tight Watt calls on energy expert Curt Klaassen, formerly with the Iowa Energy Center, to answer a Smart Choices reader’s question.

Question: I do not do well in the summer with the heat and humidity. I currently have 2 air conditioners I use for my apartment, but at times they just can’t keep ahead of the humidity at the proper temperature settings (around 77). Would I use less energy by getting a dehumidifier to work with the AC, or would it use less to turn the units down by a few degrees? –Josh

Curt’s Answer: This is a good question considering the upcoming hot and humid summer weather. You mentioned living in an apartment, and I would take that to be a typical unit in an apartment complex without a basement, crawl space, indoor hot tub, pool, sauna or other situations that affect the humidity levels in the space.

Given that as a basis, it seems that a dehumidifier would make sense to solve an elevated humidity problem. In reality, however, a basic room/area dehumidifier does remove humidity, but at the same time it adds heat to the space from the operation of its refrigeration compressor and condenser.

The net result is that your room air conditioner has to work harder to remove the added heat, using more energy. In your case, if a higher humidity level is not tolerable, it would use less energy to set the air conditioner for a lower temperature to help remove the moisture. 
One other step to take for energy efficiency: It may be prudent to note how your air conditioner cycles on and off. If the air conditioning compressor “run” or “on” cycle is short during hot weather, that may indicate an oversized air conditioner for your application.

Excessive humidity levels are a chronic problem with oversized air conditioners. In your case—with two air conditioners—it may be possible that the total capacity with both units operating is excessive. Activating one air conditioner so the compressor operates longer cycles may also provide more relief from high humidity. 

Ask Mr. Tight-watt a question or view other questions Mr. Tight-Watt has answered


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