If the problem is being caused from your AC and not a coincidental plumbing issue you have a condensation problem either the supply tap is probably improperly insulated if this not the problem the supply tap may be close to the unit and the unit has a plugged drain or is improperly insulated, next you should look at the filter (actually first) a plugged filter will slow down airflow and decrease supply air temp creating a greater chance of condensation on metal surfaces Here is a link that might be useful: Air Conditioning Repair made Easy

I would suggest a ductless split system which will be a dedicated system with its own thermostat. Sanyo or Mitsubishi brands are good. If you are not familisr with these kind af systems they have a wall mounted unit (evaporator) with a fan in it and a set of copper lines that would run down the outside of the house to the condensing unit with the compressor in it. They are very quiet and are available up to 17 SEER.

I've checked tons of people's experiences... it seems that despite the fact that it makes no sense on paper, people here get way more BTU than necessary and they say - from experience - that anything less won't do the trick. 30-day money back guarantee is not an option here, so once I buy it, I'm screwed unless I want to sell it used and lose out on the installation fee and some more. Not to mention the smallest split unit I've seen in the market was 12k BTU - which I was advised against repeatedly. Worst case scenario, I can just keep it on low, right? But I'll have wasted money on the extra tonnage.

I am with hubby. I would not want a window-shaker in the bedroom if there is any other way. You have a premium system with the ground source heat pump. Running a window unit might cost more to operate than overcooling the rest of the house. A ceiling fan might be counterproductive. You might be better off letting hot air stratify near the ceiling. High wall mount mini splits don't have to be on outside walls if you can find a way to deal with the condensate. I have 6 on interior walls and the seventh on the outside wall has its plumbing run in the stud space, not directly to the outside. You could also install a small AHU in the top of a closet or in adjacent space. Before jumping into a mini split, do make sure that your system supply and return ducts to the MBr are operating properly. Modifications to your primo GSHP system probably makes more sense than adding. Larger ducts would do it if possible. In addition to that, let's paint with a big brush and see if another zone can be added. Ask around and get recommendations for excellent HVAC pros in your area and then get them in to look at it. On the other hand, a MSHP would be very easy to operate with a small back up generator. That room might be a nice oasis in times of power outage.