It's winter in Chicago and I've found condensation dripping out in small amounts from the conduit in a ceiling fixture junction box in my kitchen. There is no light fixture attached to the box as we are doing some minor remodeling. The conduit runs through the attic above the kitchen ceiling. I have read about using duct seal to seal the conduit, but if there's already moisture in the conduit, do I need to remove the moisture first before sealing off the end? Just yesterday I added more insulation to the ceiling above the kitchen in the hopes of keeping any moisture from the bathroom and kitchen from getting into the attic.

The moisture does not come from the attic, and adding insulation,while definitely a good thing to do, will not stop the moisture from appearing in the conduit.

The moisture comes from the occupied space, enters the conduit at both open ends, and gets condensed up in the conduit, and then flows back down into the occupied space.

Yes, best to get the moisture removed as best as possible. You can blow warm air in to force out water and try to dry out the interior of the conduit. If you leave any moisure there, it will remain, and possibly corrode the conduit from the inside.

You may be best removing the wires to do this, then re- install the wires. Before pulling in the wires, you can attach a small piece of rag to pull through with a fish tape to wipe out the conduit, this may be a good way of drying out the conduit, then pull in the wires. The water will sit in the conduit at any low points of the run. Need to get it out.

Once the wires are in, then use a product called Duct Seal, a soft moldable putty sold in the electrical section of hardware stores, and certainly at electrical distributors.

Pack BOTH ENDS of the conduit, assuming both ends enter the occupied space,and any conduit that has an entry into the occupied space and runs up into the attic space. Pack the ends with as much as you can to insure a good seal, up to 2 inches in should be good. Be sure to get the putty around the wires best you can.

This will prevent moist air from entering the conduit and condensing inside.