I have not... will give that a shot. Can the humidity reading on the dehumidifier be trusted? When we plugged it in last night, it read current level to be 60%, but didn't monitor to see if it climbed any higher than that.

Type of ductwork?...is it insulated?

IMO

The humidity indicator on the cheap dehumidifers are very inaccurate. Even a cheap gauge bought on Amazon would be better. If the humidity is at 60% then I can understand why the duct work is sweating profusely. You need to bring down the humidity to at least 50%.

OK. Is there a way to do that aside from running the dehumidifier full time? And is that indicative of a problem with the way the system was set up?

The excessive humidity in the basement could be a sign the AC is over sized. Does the AC run in short cycles? Do you know the size of the AC and the size of the house? Has it been unusually humid in your area?

You may be able to use the AC itself to dry out the basement. You could install one or two supply vents at one end of the basement, and a return at the other end. The basement would become cooler but drier. You may still have to run the dehumidifier, but it should run less often.

It's a Lennox 14ACX. The house is 1800 sqft on main level and about 1500 in the basement (1100 finished). Don't notice any short cycles (and we'd likely notice, as the thing makes an loud ugly sound when it kicks on, which is another issue). Hasn't really been unusually humid.

HVAC guy coming out on Thursday. Was hoping to get a baseline "here's what I think is going on" before he came out.

Someone mentioned to me that code requires insulated duct work in unconditioned areas. I mentioned our other homes didn't have this issue, but they also had vents in the unfinished room in the basement. This is the first home without it. Anything to that?

Insulating the duct work would stop the condensation. But in my opinion you are better off controlling the humidity.

Here is the humidity monitor I use in my basement. Get a couple of these and start monitoring.

Find out the size of the AC condenser. See if the HVAC tech can slow down the blower speed. The sound you are hearing may be due to duct noise. Slowing down the air flow will help dehumidify and reduce noise.

Basements inherently have more humidity. To combat this, have your entire concrete walls and floors sealed with oil based watertite. Otherwise you will need the dehumidifier to run all the time.

It is possible your airflow is not sufficient, causing the ductwork to get very cold which will increase condensate. So possibly increase ductwork and insulate the ductwork with a vapor barrier are more solutions to try.

I would not try to use the AC to dehumidify the basement, basements typically are cold enough and if you run the AC in the basement they get uncomfortably cold.

If outdoor humidity is high, it does not take much air leakage between basement to outdoors to get high humidity down there if the temp is low. That is especially true if your return is down there and has a leak sucking in air and depressurizing the basement. What is the temp down there? Check your return for leaks and seal up any air leaks to the outdoors from the basement. (People often make the ill-advised move of opening basement windows in summer to reduce humidity. It can work under the right conditions, but that set of conditions is relatively rare.)

Ionized is right about leaks, the biggest leaks are old windows, between the sill plate and foundation wall, and between the rim joist and sill plate.

http://www.familyhandyman.com/basement/insulate-basement-rim-joists/view-all

@kanderna did you ever get this problem resolved?