Air Conditioning - Condensation on large ductwork in basment

I'm trying to determine if i have a problem and what to do.

My unfinished basement is very cold and i'm noticing that there is condensation forming on the largest rows of duct work coming out of the airconditioning unit.

The basement is so cold i can not sit in it wearing shorts and a t-shirt with out shivering.

We have both vents that come out of the ceiling duct work closed so to push the cold air up to our first and second floor but both floors are considerably warmer (they are comfortable but warmer than the basment).

We keep our temp set at 76 and leave the fan continually on, assuming that it helps keep the humidity down and prevents the air from kicking in as much (enables us to be more comfortable at a higher temp).

Anyway, any ideas or questions for me?
Thanks!

What kind of temperature comes out of the duct closest to the airhandler/furnace? And also I'd suspect your basement is real moist. And I mean moist not because of the condensation, but moist before you even turned on the a/c.

Do people shower down that basement? Or do you do lots of laundry and the dryer vent is detached and moisture from clothes stays in basement? Or do you hang up wet clothes on a clothesline down there? Or is there some other cause you can think of why it might be extra moist? Do your basement walls ever sweat? Does the basement leak in water ever?

I have seen cold water lines sweat along the basement ceiling and cause a drip line on the floor, based on the same principle. But I've personally never witnessed your problem. Yet I can easily see how that can happen.

Having the fan on 24 7 in cooling mode will make the rh go up! Heating is fine to let run. Do you know what the RH is in the basement.

Basement is not typically moist. I've even done the tin foil over night trick before we started running the A/C fan 24x7. No clothes get dried down there, laundry is done and dried on 2nd floor. Walls never sweat and no water issues at all. No flooding etc.

As far as the temp coming out near the A/C... cold! Prolly in the low 70's or lower.. not sure.

The A/C doesn't run 24/7 but there is a mode to set the fan portion of the A/C on either AUTO or ON and we leave it on the ON setting.

Not sure what RH is.. can you explain?

RH is humidity! Again keep fan on 24/7 in cooling mode will raise RH 5 to 10 percent. If you are in a green grass state a dehumidifier will be recommended to keep RH down.

To clarify regarding the fan setting your at, it was recommended that you do not leave the fan on "On", and rather put it to "Auto" so it only runs with the A/C. As airman said the fan running 24/7 raises the Relative Humidity.

That dehumidifier would help, maybe try a dessicant bag too. Our basement is partially unfinished and with the A/C on it too is quite cold, always has been, but no condensation on the ductwork. That "stack effect" is part of it, heat moving up and out keeping underground and basements cooler. In fact, with our A/C off completely, the upstairs is unbearable but the basement is just fine.

Good luck!

Sorry it's taken me a while to reply..

As far as the RH, there's a dial on the side of our A/C unit in the basement. We have it set to the recommended 40%... is that bad?

Sounds like you are describing the humidistat for your humidifier. If so, it needs to be off during the summer months. Maybe I'm misunderstanding but I have many customers that don't know that they don't need it on year round. Also if it's a humidifier, check to see if there is a damper that needs to be closed during air conditioning season.

I think tinmantu hit the nail on the head! If your humidifer is not shut off properly, then you are adding humidity while trying to take it away. Double check, your problem might just disapear.

There is a small dial attached to the wall of my A/C unit. It states on it something to the effect.. "When the temp outside is XX.. set dial to XX"

Right now it says when temp is above 70 degrees F set to 40% so that's where i have it set.

Also turning the Fan off 24/7 helped with the condensation problem in the basement.