We are moving to a CONDO (so no common prop alterations possible) Our bedroom opens into a sun-room (that in turn opens outside via a sliding glass door) so our bedroom has French doors and a non-opening window, but they both lead into the sun room, not outside.

Question - if we replaced the non-opening bedroom window with a slider window that opened (because that would not be common property?) then we could use an AC in the bedroom that vented through that window into the sunroom - would this be OK to do? It would heat up the sun room but we would lock the sliding glass door leading to the outside open.

  • Where is this condo? I gather it does not have a central a/c unit so presumably it is in a mild or cold climate? May 26 '17 at 23:55

A "ductless" a/c system would appear to be the solution for this condo. You must exhaust the heat and humidity to the outside. Google "ductless mini split a/c".

Having a window a/c unit exhaust to the sun room would be completely unacceptable. A window unit used in this way would be by far the cheapest way to cool the bedroom, but would destroy the utility and aesthetics of the sun room. It would almost certainly be rejected by the condo association.

The condensing unit of the ductless system would be on the ground outside or hung on the outside wall and the air handler/evaporator on the wall in the bedroom. Refrigerant and electrical lines would connect the two units. The tubing to carry away the condensed water could presumably follow the same path and drip onto the ground outside.

  • It sounds like the OP isn't allowed to place a condensing unit outside ("No common prop(erty) alterations").
    – Tester101
    May 26 '17 at 21:30

It will heat up the sun room AND drastically increase the humidity in that room. High humidity can cause mold and damage to drywall. That's why exhaust fans and moisture resistant drywall are required in bathrooms.

If it isn't too long of a distance, running an exhaust vent from your bedroom window to the sliding door in the sunroom might be better. You'd need to make a frame that blocks the doorway out of door or something to mount the exhaust to. Of course, that makes it harder to actually use the door.

Otherwise, I'd probably give it a shot, but monitor the humidity in the sunroom with a hydrometer. You can find charts online for what the maximum recommended humidity is at various temperatures. If it's getting high enough that condensation starts forming, you will eventually have a mold problem.

Also consider how well insulated and sealed the walls and doors between the sun room and the rest of the condo are. If they aren't insulated, or aren't insulated well, the heat will just be sucked back in.

  • 2
    Why would it increase humidity? A/C generally removes water vapor on the cool side, and does not add it on the hot side. The liquid water it condenses goes "somewhere" but should stay liquid. May 26 '17 at 18:05
  • That said, it needs somewhere to drain.
    – isherwood
    May 26 '17 at 18:18
  • @harper depends on the kind of air conditioner. I forgot window mounted ones usually just drip the water somewhere. I'm stuck with portable floor units (windows not wide enough for a window mounted one), and they rely on evaporating the water and exhausting it along with the air. So you'd want to stay away from portable ACs.
    – Grant
    May 26 '17 at 18:40
  • 1
    Really? I had always assumed portable A/Cs had a tank like a dehumidifier that you had to empty at intervals. Perhaps because I did have one like that. Thermodynamically that works (air made 20 degrees hotter can hold more water than air made 20 degrees colder can lose). But it seems like making the condenser wet would shorten its life. May 26 '17 at 18:46
  • @Harper yep, at least all the ones I've seen. They vent moist air. If the indoor humidity is too high, there is a tank inside that fills up, but under normal conditions they don't require draining except before storing them.
    – Grant
    May 26 '17 at 18:48

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