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I have an LG 7000btu portable a/c [LP0711WNR] unit that I would like to use in a basement area solely as a dehumidifier. Do I need to vent the exhaust to the outside or can it just exhaust back into the basement? Specifically, does the water vapor condense inside the unit and go out the drain or is it turned into vapor and blown out the exhaust making outside exhaust necessary? Thank you.

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    Having felt the exhaust off my portable unit, I can say that most do blow a lot of the moisture out the exhaust unlike a purpose built dehumidifier. It would only serve to generate a significant amount of heat if you did not vent outside. Otherwise you will only warm your moist air, causing other problems. – BrownRedHawk Aug 19 '16 at 13:08
  • If you run an AC unit in a closed space the condensate / humidity will be removed. The problem with a portable unit is that you will need to regularly empty the condensate. Just a note that the over room temperature will also be increased by the amount of energy the AC unit consumes. Vent outside in the summer and run enclosed in the winter may not hit the pocket book as hard and dehumidify the area. – Ed Beal Aug 19 '16 at 13:09
  • @BrownRedHawk, The evaporator the part that makes the air cold and removes the Humidity is enclosed and totally separate and from the condenser. the only difference in a purpose built dehumidifier and AC unit is the condensate container and on better models the humidity controls. Some kind of drip tray or bucket will needed to catch the portable AC unit condensate. – Ed Beal Aug 19 '16 at 13:36
  • @EdBeal Having serviced one of my units that had a bad fan, the unit purposefully diverts condensate onto the evaporator as a way to make it more efficient, as well as blow out the now evaporated water with the hot air. Makes for a very cool, dry air, and I rarely have to empty the overflow condensate tray. – BrownRedHawk Aug 19 '16 at 13:42
  • All of the units I have worked on are supposed to be tilted so the back is lower this allows the condensate to drip out the back. I do have a universal 608 & 609 HVAC licenses so I am not just guessing. – Ed Beal Aug 19 '16 at 13:51
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In theory, this will work just fine if you provide a way to collect the condensed water from the evaporator (the finned heat exchanger where the working fluid is evaporated to take heat from the "indoor" air). However, note that the more efficient window units take this water and spray it against the condenser (the other finned heat exchanger where the working fluid is condensed to pump heat into the "outdoor" air). This increases efficiency by making it easier for the condenser to transfer heat to the outdoor air (see heat of evaporation).

This is great for an air conditioner, but if you try to use such a unit as a stand-alone dehumidifier, with both intake and exhaust in the same room, then you'll just be pumping heat AND humidity from one side to the other, with no net gain (except for heating your basement). It's possible that you could intercept this transfer of water from the "indoor" to the "outdoor" side, but that would completely depend on the design of the air conditioner.

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We have a portable dehumidifier that is nothing but a small air conditioner made more convenient with wheels and a drain port for attaching a hose and an included bucket if you don't attach a hose. The exhaust blows into the basement and, since the basement is far cooler than the rest of the house and we don't do anything down there, any added heat never bothers us, nor is it noticeable.

It also has a humidity detector and turns itself on and off based on that, not temperature. This will be your only real issue with using an AC unit.

Other than that, there is no difference.

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